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A Guide for New Zealand Beekeepers
CONTROL OF VARROA
CONTROL OF VARROA
A Guide for New Zealand Beekeepers
has been published by the Ministry of Agriculture and Forestry as
part of its on-going assistance to the New Zealand beekeeping
industry following the recent discovery of this important new
honey bee pest.
The guide aims to give beekeepers the practical tools they will
need to minimise the effects of varroa while continuing to produce
wholesome bee products and provide vital pollination services.
The guide reviews the world literature on varroa control and puts
the information in a straightforward, easy-to-reference form that
will be useful to all beekeepers, whether they are hobbyists, or
commercial producers.
With 7 diagrams and 24 colour plates.
Mark Goodwin is a senior scientist at the Horticulture and Food
Research Institute (HortResearch), and is playing a leading role in
New Zealand’s research efforts in varroa control.
Cliff Van Eaton is also an apiculture scientist at HortResearch,
and is a long-time advisor to New Zealand beekeepers.
Together they have also written Elimination of American foulbrood
without the use of drugs, published by the National Beekeepers’
Association of New Zealand in 1999.
© New Zealand Ministry of Agriculture and Forestry
ISBN 0-478-07958-3
i
CONTROL OF VARROA
A Guide for New Zealand Beekeepers
by
Mark Goodwin and Cliff Van Eaton
New Zealand Ministry of Agriculture and Forestry
ii
© Copyright 2001 by
New Zealand Ministry of Agriculture and Forestry
PO Box 2526, Wellington, New Zealand
ISBN 0-478-07958-3
Printed in New Zealand by Astra Print, Wellington
Production by Words & Pictures, Wellington
iii
IMPORTANT DISCLAIMER
This book is a guide on the range of control methods available for the treatment of varroa.
The control methods discussed will not be appropriate in every situation.
The Crown, its employees and consultants do not accept any responsibility or liability
whatsoever for any error of fact, omission, interpretation or opinion which may be present,
however it may have occurred, nor for the consequences of any decision based on the
information in this publication.
Without in any way limiting the above statement, the Crown, its employees and
consultants expressly disclaim all and any liability to any person in respect of anything,
and the consequences of anything, done or omitted to be done in reliance, whether wholly
or partly, upon the whole or any part of the contents of this publication.
iv
It is illegal in New Zealand to use a chemical substance to control varroa
that has not been registered or approved by the New Zealand government.
INFORMATION ON VARROA CONTROL PRODUCTS
Mention in this guide of companies or commercial products does not imply
recommendation or endorsement by the New Zealand Ministry of Agriculture and Forestry
over any others not mentioned.
Mention in this guide of varroa control substances not currently registered or approved for
use in New Zealand does not imply that such substances should be used unless and until
registration or approval is obtained.
The following products mentioned in this guide are registered trade names:
Apicure
Apiguard
Apilife VAR
Apistan
Apitol
Apivar
Bayvarol
Check-Mite+
Folbex
Mavrik
Mite Away
Perizin
Tween
v
ACKNOWLEDGEMENTS
Mark Goodwin is a senior scientist with the Horticulture and Food Research Institute of
New Zealand Ltd (HortResearch), and is stationed at the Ruakura Agriculture Centre in
Hamilton. Mark and his team have conducted extensive work in the fields of honey bee
pollination and American foulbrood control, and he is now playing a leading role in
New Zealand’s research efforts in varroa control.
Cliff Van Eaton is an apiculture scientist with HortResearch. Cliff has been an
Apicultural Advisory Officer with MAF Quality Management, and was national manager
for the American Foulbrood Control Programme from 1991 to 1998. He is co-author with
Mark Goodwin of Elimination of American foulbrood without the use of drugs, published
by the National Beekeepers’ Association of New Zealand in 1999.
The authors wish to acknowledge the assistance and support of HortResearch and
Comvita NZ Ltd in the research and writing of this publication, and the following
individuals and institutions who kindly reviewed the initial draft:
• Mike Brown and colleagues, CSL National Bee Unit, UK Ministry of Agriculture,
Fisheries and Food
• Paul Brown, New Zealand
• John Gates, British Columbia Ministry of Agriculture, Fisheries and Food, Canada
• Henrik Hansen and Camilla Brødsgaard, Ministry of Food, Agriculture and
Fisheries, Denmark
• Andrew Matheson, Ministry of Agriculture and Forestry, New Zealand
• Sarah and Simon Peacey, New Zealand
• Murray Reid, AgriQuality NZ Ltd, New Zealand
• Peter Sales, New Zealand
• Hachiro Shimanuki, US Department of Agriculture (retired), USA
Picture Credits
Ambrosiushoeve Research Centre for Insect Pollination and Beekeeping – Figure 2.4
Bee Research Laboratory, US Department of Agriculture – Figure 2.1
CSL National Bee Unit, UK Ministry of Agriculture, Fisheries and Food – Figures 2.2,
3.2, 5.2
Keith Pegram – Figure 8.2
Mid-Atlantic Apiculture Research and Extension Consortium – Figures 2.6, 3.1, 5.3
University of Nebraska Institute of Agriculture and Natural Resources – Figure 5.6
HortResearch – all others
1
TABLE OF CONTENTS
DISCLAIMER PAGE ........................................................................................... iii
INFORMATION ON VARROA CONTROL PRODUCTS .............................................. iv
ACKNOWLEDGEMENTS PAGE.............................................................................. v
ESSENTIALS OF VARROA CONTROL ................................................................... 5
1. INTRODUCTION .......................................................................................... 9
1.1 History of varroa ............................................................................ 9
1.2 The future ................................................................................... 10
1.3 Aim of this guide ......................................................................... 11
2. VARROA BIOLOGY ..................................................................................... 13
2.1 Varroa on adult bees .................................................................... 13
2.2 Varroa on bee brood ..................................................................... 14
3. EFFECTS OF VARROA ................................................................................ 16
3.1 Effects on bees ........................................................................... 16
3.1.1 Effects of varroa feeding on adult bees .......................................... 16
3.1.2 Effects of varroa feeding on honey bee larvae or pupae .................... 17
3.2 Effects on colonies ...................................................................... 18
3.2.1 Effects on feral colonies ............................................................... 19
3.2.2 Parasitic mite syndrome ............................................................... 19
3.2.3 Effects on colony production ......................................................... 21
3.2.4 Effects on numbers of managed colonies ....................................... 22
3.3 Effects on pollination ................................................................... 23
4. VARROA POPULATION GROWTH................................................................. 24
4.1 Reproduction rates ...................................................................... 24
4.2 Understanding varroa population growth ........................................ 24
4.2.1 Reproduction and population growth ............................................. 24
4.2.2 Invasion and population growth ..................................................... 26
4.2.3 Acute versus chronic infestation .................................................... 27
4.2.4 Effects of control on population growth rates .................................. 28
5. DETECTION AND EVALUATION OF INFESTATIONS ....................................... 29
5.1 Why sample hives for varroa .......................................................... 29
5.2 Identifying varroa ......................................................................... 29
5.3 Detection methods ....................................................................... 30
5.3.1 Sampling bees ............................................................................ 31
5.3.2 Visual inspection of bees .............................................................. 32
5.3.3 Visual inspection of brood ............................................................ 32
5.3.4 Ether roll .................................................................................... 33
5.3.5 Soapy water or alcohol ................................................................. 34
5.3.6 Sugar shake ................................................................................ 35
5.3.7 Tobacco smoke ............................................................................ 35
5.3.8 Mesh bottom boards .................................................................... 36
5.3.9 Apistan, Bayvarol and formic acid ................................................. 37
5.4 Sticky boards .............................................................................. 37
5.5 Using mite population estimates ................................................... 38
6. CHEMICAL CONTROL ................................................................................ 40
6.1 Chemical safety ........................................................................... 40
6.2 Synthetic chemicals ..................................................................... 41
6.2.1 Fluvalinate (Apistan) .................................................................... 41
6.2.2 Flumethrin (Bayvarol) ................................................................... 42
2
6.2.3 Coumaphos (Check-Mite+, Perizin) ................................................ 43
6.2.4 Cymiazole (Apitol) ........................................................................ 43
6.2.5 Bromopropylate (Folbex) ............................................................... 43
6.2.6 Amitraz (Apivar) .......................................................................... 43
6.3 Organic chemicals ....................................................................... 44
6.3.1 Essential oils ............................................................................... 44
6.3.2 Organic acids .............................................................................. 46
6.3.3 Vegetable and other oils ............................................................... 50
6.3.4 Icing sugar .................................................................................. 50
6.3.5 Outlook for organic chemical controls ............................................ 51
6.4 Avoiding chemical residues ........................................................... 51
7. CHEMICAL RESISTANCE............................................................................ 53
7.1 What is chemical resistance? ........................................................ 53
7.2 Why resistance happens ............................................................... 53
7.3 Creating resistant varroa in the laboratory ....................................... 54
7.4 How beekeepers have created resistant varroa ................................ 54
7.4.1 Use of Mavrik .............................................................................. 54
7.4.2 Incorrect use of miticide strips ...................................................... 55
7.5 Cross-resistance .......................................................................... 55
7.6 Slowing resistance ....................................................................... 55
7.7 How to measure resistance ........................................................... 56
8. BIOTECHNICAL CONTROL ......................................................................... 57
8.1 What does ‘biotechnical’ mean? .................................................... 57
8.2 Brood removal and trapping .......................................................... 57
8.2.1 Worker brood removal ................................................................... 57
8.2.2 Drone brood trapping ................................................................... 57
8.2.3 The hive splitting varroa control method ......................................... 58
8.2.4 Queen isolation cages .................................................................. 60
8.3 Mesh bottom boards .................................................................... 60
8.4 Pollen traps ................................................................................ 62
8.5 Heat treatment ............................................................................ 62
8.6 Change of cell size ....................................................................... 63
8.7 Eliminating the production of drone brood ..................................... 63
9. BREEDING FOR VARROA TOLERANCE ........................................................ 64
9.1 What is varroa tolerance? .............................................................. 64
9.2 Varroa tolerance mechanisms ........................................................ 64
9.2.1 Apis cerana ................................................................................. 64
9.2.2 Hygienic behaviour ...................................................................... 65
9.2.3 Duration of capped stage .............................................................. 65
9.2.4 Suppression of mite reproduction .................................................. 66
9.2.5 Attraction of mites to brood .......................................................... 66
9.2.6 Grooming .................................................................................... 67
9.3 Examples of breeding programmes for varroa tolerance .................... 67
9.3.1 Russian stocks ............................................................................ 67
9.3.2 Arizona practical breeding programme ........................................... 67
9.3.3 Selecting for shorter capped period ............................................... 68
9.3.4 Selection for low varroa infestation levels ....................................... 68
10. INTEGRATED PEST MANAGEMENT............................................................. 69
10.1 History of pesticide use in New Zealand ......................................... 69
10.2 What is integrated pest management? ............................................ 69
3
10.3 Economic threshold ..................................................................... 70
10.4 Monitoring .................................................................................. 70
10.5 Decision-making and control ......................................................... 71
11. TIMING OF VARROA CONTROL ................................................................... 73
11.1 Factors affecting timing of varroa control ....................................... 73
11.2 Treatment programme types .......................................................... 73
11.2.1 Prophylactic treatment ................................................................. 73
11.2.2 Calendar treatment ...................................................................... 74
11.2.3 Treatment based on monitoring and economic thresholds (IPM) ....... 74
11.3 Reducing residues ....................................................................... 75
11.4 Changes to management .............................................................. 75
11.5 Co-ordinated treatments ............................................................... 75
11.6 Spring and autumn treatments ...................................................... 76
12. CONTROL METHODS USED OVERSEAS ...................................................... 77
12.1 British Columbia, Canada ............................................................. 77
12.2 Georgia, USA .............................................................................. 78
12.3 Arizona, USA ............................................................................... 79
12.4 United Kingdom .......................................................................... 80
12.5 Denmark ..................................................................................... 82
12.6 Vietnam ...................................................................................... 83
MANAGEMENT PLANS TO CONTROL VARROA ................................................... 85
APPENDIX 1. Estimating mite populations in hives ............................................. 90
APPENDIX 2. How to use formic acid ................................................................. 92
APPENDIX 3. How to use oxalic acid .................................................................. 97
APPENDIX 4. How to use thymol ....................................................................... 99
APPENDIX 5. Varroa chemical resistance test ................................................... 101
APPENDIX 6. Regulatory and legal issues related to movement controls .............. 103
APPENDIX 7. Regulatory and legal issues related to treatment ........................... 104
SUGGESTED READING .................................................................................. 105
USEFUL CONTACTS ....................................................................................... 109
TERMS AND ABBREVIATIONS USED IN THIS GUIDE ....................................... 110
INDEX ............................................................................................... 114
4
5
ESSENTIALS OF VARROA CONTROL
Why should you control varroa?
If left uncontrolled, varroa will eventually kill your honey bee colonies. You can
successfully keep bees in areas where varroa has become established, but you will need to
use control methods on a regular basis to reduce mite numbers so they do not seriously
affect your hives.
What follows is a very brief summary of varroa control methods presented in this guide.
The numbers in brackets identify chapters and sections where important information is
discussed in greater detail.
Do your bees have varroa?
The first step is to determine whether your honey bee colonies have varroa. To do this you
need to know what varroa looks like and be able to distinguish it from melittiphis, a
smaller mite that is also found in hives.
Varroa mites have a reddish to dark brown body that is flattened and oval (2.1). Melittiphis
is about one quarter the size of varroa and is different in shape. It does, however, tend to
be similar in colour to varroa (5.2).
How should you look for varroa?
Don’t rely on visually inspecting adult bees for varroa. Because varroa often hide between
the plates of a bee’s abdomen, you are not likely to see the mites on bees unless the
varroa population in the colony is very high (2.1 and 5.3.2).
Change your beekeeping management to effectively sample your hives for varroa on a
regular basis. There are a number of very good methods you can use (5).
What varroa sampling method should you use?
If varroa hasn’t been reported in your area, you should use a very sensitive sampling
method. The most accurate and easiest is Apistan or Bayvarol put into a hive for 24 hours,
together with a sticky board to collect the mites that are killed (5.3.9). Since varroa prefer
to reproduce on drone brood, checking capped drone brood with a cappings scratcher can
also be a sensitive test (5.3.3).
If varroa is in your area, you need to survey your hives throughout the beekeeping season
to determine if mite populations are reaching potentially damaging levels. Washing a
sample of bees in soapy water (5.3.5), using the sugar shake method (5.3.6), or checking
natural mite fall with mesh bottom boards (5.3.8) are all reliable methods.
To decide if mites are reaching damaging levels, you can use the thresholds for these
sampling methods presented in chapter 5, or you can calculate the total mite population
for a colony using the formulas in appendix 1.
When should you apply a varroa control?
If mites have only just moved into an area during the year and your colonies have very few
mites (less than 20 per hive), it probably isn’t worth applying a varroa control immediately.
ESSENTIALS OF
VARROA CONTROL
6
However, in the second and following years after varroa has been found, it is very
important to survey hives in every apiary on a regular basis to ensure mite numbers don’t
sneak up on you. In the acute phase (4.2.3), mite invasion from other colonies can be
very high, especially in late summer and early autumn (4.2.2).
During the acute phase, you should treat all of your hives for varroa as a matter of routine,
rather than relying solely on survey results (11.2.2). Control should always be carried out
at least in the spring and autumn, and at other times during the season if surveying shows
that it is required.
What should you do differently in spring?
It is important to have good mite control in spring because the large amounts of brood in
the hive will provide ideal breeding conditions for the mite. Not providing a high level of
control in spring can result in colonies collapsing before the autumn treatment (11.6).
When inspecting your hives in spring, parasitic mite syndrome may make it more difficult
to diagnose other brood diseases. Get a laboratory diagnosis if half-moon shaped larvae
are found in a colony because both parasitic mite syndrome and European foulbrood can
have the same symptoms (3.2.2).
What should you do differently in summer?
Because mites can invade your colonies after the treatment, you should sample at least
once in the summer between treatments in case mites have built up to damaging levels
again very quickly. If this is the case, you will need to remove the honey from the hives
and treat them again.
What should you do differently in autumn?
Don’t be complacent just because your hives have strong populations and are producing a
good honey crop. If honey isn’t removed as soon as the flow has ended and treatment
carried out, good colonies are likely to collapse suddenly during autumn as a result of
mite invasion (3.2.3).
You may need to change your beekeeping management to remove your honey earlier than
you have in the past. Even forgoing some honey production is not as bad as losing
colonies to varroa (11.4).
Beekeepers around the world have been caught out by varroa invasion in autumn. Don’t
let strong colonies fool you. Apply an effective varroa control.
What control methods should you use?
A number of organic (6.3) and synthetic chemicals (6.2) are used world-wide to control
varroa. It is very important, however, to only use compounds that have been registered or
approved for varroa control in New Zealand.
Make sure you follow control product label directions exactly. They have been written to
protect you, your bees and the people who consume your bee products (6.1).
There are also a number of control methods that rely on hive manipulation (8). However,
most of these methods are time-consuming, and may not by themselves provide adequate
varroa control, especially during the acute phase.
CONTROL OF VARROA: ESSENTIALS OF VARROA CONTROL
ESSENTIALS OF
VARROA CONTROL
7
During the acute phase, you will not only want to control varroa in your hives, you will also
want to reduce mite invasion. Choosing a method that offers control for an extended
period of time is therefore important. Apistan (6.2.1) or Bayvarol (6.2.2) both provide very
good mite control and also offer protection over six to eight weeks. Formic acid in a pouch
(6.3.2.1) can also provide good extended control, although handling formic acid is
potentially hazardous (appendix 2).
How can you tell if the control method has worked?
After applying a mite control, it is important to sample some of your colonies again to
make sure mite populations have been reduced to low levels (10.4). If mite numbers are
still high, you will need to re-apply a control, even if this means removing the honey from
your hives.
How can you minimise residues from mite control chemicals?
You need to be careful when using mite control chemicals to minimise residues in bee
products (6.4). The best way to do this is by carefully following the instructions on the
product label. It is especially important not to use control chemicals when there are
honey supers on a hive.
How can you help avoid mites developing chemical resistance?
Varroa can develop resistance to chemical controls (7). To help avoid resistance, you
should use different control products in the spring and autumn (7.6).
All varroa control products should also be used according to the label, and they should
especially not be left on hives for longer than recommended (7.4).
If your control does not appear to be working, a sample of mites from your colonies should
be tested for resistance (7.7).
When can you start reducing your use of chemical controls?
Integrated pest management programmes are designed to reduce beekeepers’ use of mite
control chemicals (10). However, it is important to apply these chemicals on a regular
basis until varroa has destroyed most feral colonies and mite invasion has reduced.
Once the acute phase is over, you will better be able to predict mite population growth in
your colonies and tailor your control programme accordingly. You will also be able to use a
greater variety of control methods, including biotechnical measures, which together may
provide effective control.
CONTROL OF VARROA: ESSENTIALS OF VARROA CONTROL
ESSENTIALS OF
VARROA CONTROL
8
Varroa Control – Simple Do’s and Don’ts
Do:
✓ Change your beekeeping to
regularly survey for varroa.
✓ Routinely apply a control in the
spring and autumn during the
acute phase.
✓ Survey hives at least once in the
summer in case mite levels have
built up quickly again.
✓ Apply mite control if varroa
numbers are high, even if honey
supers have to be removed.
✓ Remove your summer honey crop
earlier than in the past.
✓ Follow varroa control product label
directions exactly.
✓ Choose a control method that
offers control over an extended
period to reduce mite invasion.
✓ Use a different control product in
the spring and autumn.
✓ Have a sample of mites tested if a
control product doesn’t seem to
be working.
Don’t:
✗ Rely on visually inspecting adult
bees for varroa.
✗ Be complacent about varroa just
because your hives are strong and
are producing a good crop.
✗ Take your honey off late in the
season and only then decide to
apply a varroa control.
✗ Get caught out by varroa invasion.
✗ Use compounds that haven’t been
registered for varroa control.
✗ Assume your mite control has
worked without checking.
✗ Apply control chemicals when
there are honey supers on the
hive.
✗ Leave a control product on hives
longer than the label says.
✗ Consider reducing chemical
controls until after the acute
phase is over.
Words of Wisdom from Overseas…
Colonies infested with varroa can appear completely normal,
lulling you into a false sense of security.
But when population levels of the mite build up, damage can
occur suddenly and swiftly, often wiping out colonies and
catching you by surprise.
The failure to appreciate this fact is the main reason
beekeepers lose colonies even after they know they have varroa.
CONTROL OF VARROA: ESSENTIALS OF VARROA CONTROL
ESSENTIALS OF
VARROA CONTROL
9
1. INTRODUCTION
1.1 History of varroa
Varroa disease, or ‘varoosis’, is caused by the external parasitic bee mite Varroa
destructor, known until recently as Varroa jacobsoni. Varroa’s scientific classification
was changed in 2000 when it was determined that the mite commonly infesting the
European honey bee (Apis mellifera) around the world was actually a different species
from the one first identified on the Asian honey bee (Apis cerana) in Java in 1904.
Varroa mites were originally parasites of Apis cerana, and the two species have probably
existed together for hundreds of thousands of years, with the mite killing a few colonies
but never enough to endanger A. cerana as a species. The reason, of course, is that
without the bees the mite would also die. Evolution treats harshly any parasite or
predator that does not obey this basic rule.
However, by 1963 varroa had jumped species and could be found on Apis mellifera in
the Philippines, Japan, Vietnam and Russia. On a new honey bee species that had little
resistance to it, varroa didn’t follow the parasites’ rule, and since then it has killed
millions of European honey bee colonies in Asia, Europe, the Americas and Africa.
By 1999, varroa had been reported in most beekeeping areas of the world with the
exception of Australia and New Zealand. This changed in April 2000 when the mite
was found in Auckland. The survey that followed confirmed a large number of colonies
infested in the Auckland region and northern Hauraki Plains. Isolated infestations were
also found in hives in the Hokianga, Te Puke, Otorohonga and the Taumarunui area
(figure 1.1).
After consultation, the New Zealand government decided an attempt to eradicate varroa
would be unlikely to succed, and adopted a managed control programme instead.
Varroa can be expected to spread over all of the North Island and eventually to all of the
South Island, although it is hoped that the movement controls established by
government will help to slow this spread.
Figure 1.1 Reported distribution of varroa in New Zealand in October 2000 (red spots).
Hokiangia
Auckland
Otorohanga
Taumarunui
Te Puke
INTRODUCTION
10
1.2 The future
The finding of varroa has changed forever the practice of beekeeping in New Zealand. We
have always prided ourselves on the high-health status of our honey bee stocks and the
fact that we do not use antibiotics to control American foulbrood disease. Our beekeeping
industry has benefited greatly from these things, and we have developed world-respected
trades in honey bee stocks and value-added honey bee products.
We still have a beekeeping industry that is the envy of most, but we also have a new test
of our abilities and resources. Now, like most of the rest of the world, we must face one of
the most devastating parasites of honey bees.
While the finding of varroa has been a tragedy for everyone involved in beekeeping in this
country, we are at the same time fortunate to be one of the last places on earth to feel the
effects of the mite. Varroa has been the greatest topic of beekeeping research world-wide
in the last 20 years. Much has been learnt about the mite’s biology, its impacts, and most
importantly how it can be controlled.
The presence of varroa in New Zealand will result in greater changes in beekeeping
practices than it has in many other places. This is because beekeepers here have
generally not resorted to chemicals to control the relatively few honey bee diseases and
pests that are present.
The need to control varroa will require a shift in the belief systems for most New Zealand
beekeepers – a shift from being ‘natural’ producers, to producers that cannot survive
without the use of pesticides; from thinking of pesticides as something that kills bees, to
thinking of them as products that ensure the bees’ survival. And with this change in belief
systems comes a whole range of new concepts such as monitoring, economic thresholds,
timing of treatments, resistance and residues.
Although the change is large for beekeepers, we have a well-organised and sophisticated
industry that is better placed than many to meet the challenge. Our world-leading
approach to AFB control and our highly organised pollination industry are just a couple of
examples of what we know we can do.
There is no simple recipe that will win the battle against varroa. The mite has so far
proven too resourceful for that, and much more investigation and innovation still
needs to take place. However, in New Zealand we can employ methods well-proven
overseas to reduce the effects of the mite, and we can also trial more speculative
techniques to develop a uniquely ‘kiwi’ approach that will carry on our reputation of
beekeeping excellence.
The success with which individual beekeepers meet the challenges ahead will depend on
how well they are able to adapt to the changes required. Unfortunately, varroa is a
problem that cannot be ignored. There is no doubt that beekeepers who learn from
overseas experience with varroa, and in time the experience of their fellow beekeepers
here in New Zealand, will cope with the mite and maintain profitable beekeeping.
However, those who chose to ignore the mite, or hope it will go away, will also likely follow
the path seen overseas, and will no longer remain part of the beekeeping industry in the
years to come.
CONTROL OF VARROA: INTRODUCTION
Success in fighting varroa will depend on how well beekeepers are able to
adapt to changes required in their beekeeping management.
INTRODUCTION
11
Overseas experience has shown that many beekeepers go through a learning process with
varroa that has the following steps:
1. do nothing about varroa control because their hives look good (large populations,
good crops);
2. experience sudden colony collapses and large losses;
3. carry out regular varroa control treatments following the calendar;
4. begin to monitor their hives in an attempt to reduce chemical use;
5. develop a good understanding of varroa population growth in their own area;
and finally,
6. develop a good varroa control programme based on this understanding.
The purpose of varroa control education is to minimise the effects of the first two steps in
this process, and to ensure management changes are made so that the endpoint of the
process is reached as soon as possible.
1.3 Aim of this guide
This guide aims to provide beekeepers with the practical tools they will need to minimise
the effects of varroa while still maintaining the industry’s core values of environmental
responsibility and the need to remain economically viable.
As authors, we are certainly not specialists in varroa control, and like almost everyone
keeping bees in this country we only have a small amount of experience of the mite in
New Zealand conditions. The purpose of this guide is therefore not to offer a proven set of
New Zealand-based prescriptions along the lines of the authors’ book entitled Control of
American foulbrood without the use of drugs.
The guide is instead an attempt to review the world literature on varroa and put it in an
orderly, easy-to-reference form that makes sense to beekeepers. There are a number of
concepts that will be foreign to most New Zealand readers, which is expected given the
newness of the mite to our beekeeping. However, we hope we have explained them well
enough so they become part of our normal vocabulary as we all learn to deal with varroa.
The guide also does not attempt to provide a complete summary on all that is known
about the subject. We have instead only included information we considered useful for
understanding how varroa can be controlled.
While this guide is based on overseas research, it is important to remember that it is
difficult to predict how the mite will behave throughout New Zealand. Although the
conditions within our beehives are very similar to overseas, our bees have been genetically
isolated from the rest of the world for more than 50 years, we have fewer pathogens for
varroa to interact with, and there are differences in the way we manage our bees. Climatic
differences between the northern and southern areas of New Zealand may also cause
varroa to have varying effects, and the situation in New Zealand is also changing quickly
as varroa spreads and new pesticides are being registered and used.
Nevertheless, utilising international experience is an invaluable first step as we learn to
live with varroa in New Zealand. Using and adapting overseas techniques is better at the
outset than trying to develop local methods from scratch.
CONTROL OF VARROA: INTRODUCTION
INTRODUCTION
12
CONTROL OF VARROA: INTRODUCTION
This guide is a review of the world literature on varroa; produced
for New Zealand beekeepers, not a proven set of New Zealandbased
varroa control methods.
INTRODUCTION
At the same time we hope that the guide will be revised in several years as new research
findings and management techniques for varroa control are developed, both overseas and
particularly in New Zealand.
13
2. VARROA BIOLOGY
This chapter describes varroa and explains its lifecycle.
2.1 Varroa on adult bees
Adult female varroa mites (figure 2.1) are fairly large (1.1 x 1.6mm) and have a hard,
reddish to dark brown body that is flattened and oval in shape. Male mites are smaller than
females, and are rarely seen since they are only found inside brood cells.
Varroa are quite fast moving when not in brood cells and can run
quickly over the comb surface. When they are being carried on
adult bees, they frequently crawl under the overlapping
abdominal plates where they feed on haemolymph (bee blood).
Because of this behaviour, mites can reach a high population
within a colony even though only a few varroa will be easily
visible on adult bees (figure 2.2).
An example from work carried out by HortResearch illustrates
how hard it is to see varroa on adult bees. As part of a trial in
South Auckland, samples of 200 bees were needed that were
heavily infested with mites. However, the colonies themselves
didn’t appear to have many varroa. So the researchers made
sure they put three bees that visibly had mites into
each sample jar before filling the jar with other bees
from a hive. This ensured each sample had at least
three varroa, even though it took quite a while to
find the visibly infected bees. However, when the
200 bee samples were processed for varroa in the
lab, between 100 and 150 varroa were recovered
from each jar.
Varroa usually only stay on adult bees for about
7 days before entering an uncapped cell with a
larva. They do, however, stay on bees for much
longer than this when there is no brood in a colony.
Very few of these mites are removed and killed by
worker bees. Studies show that varroa can only
survive away from bees or honey bee brood for
about 51/2 days, but they can live on adult bees for long periods of time. We know this
because the mite is able to survive long broodless periods during severe winter conditions.
Figure 2.1 Adult female
varroa mite.
Figure 2.2 Two varroa mites on a bee.
The top-most mite has crawled between
the bee’s overlapping plates of the bee’s
abdomen and is partially hidden.
Mites find their way into colonies through beekeepers exchanging equipment between
hives, bees with varroa drifting between colonies, and bees robbing colonies weakened
by varroa.
Although varroa has been seen on other insects (and sometimes even on beekeepers
when they have just finished working a hive), the mites can only reproduce on honey
bee brood.
Varroa can reach high population levels in a honey bee colony even
though few mites are visible on the adult bees.
BIOLOGY
14
2.2 Varroa on bee brood
The life cycle of varroa is presented in figure 2.3. Adult female varroa leave adult bees
and invade either worker cells about 20 hours before they are capped, or drone cells
40 hours before they are capped. The mites prefer to invade cells containing drone
larvae. Drone cells are 8 to 10 times more likely to contain varroa than worker cells.
Varroa can survive for long periods on adult bees.
Figure 2.4 Varroa on drone prepupae.
Figure 2.5 Adult female varroa on a
drone pupa.
CONTROL OF VARROA: VARROA BIOLOGY
On entering a cell, the female mite crawls down to the bottom and submerges itself in the
larval food. Within the first 4 hours of the cell being capped, the mite leaves the larval
food and starts feeding on the haemolymph of the prepupa (figure 2.4). ‘Feeding sign’
(which is actually mite faeces) appear as white dots at the hind end of the prepupa.
Feeding sign can also be seen on the walls of
brood cells once the adult bee has emerged.
The mite lays its first eggs about 60-70 hours after
the cell is sealed. Varroa usually deposit 5-6 eggs
in a cell, the first of which is usually a male, with
the remainder female.
After the egg hatches, the mite goes through two
juvenile stages (protonymph and deutonymph)
before finally reaching maturity and taking on the
adult body shape (figure 2.5).
The mother mite establishes a feeding site on the
pupa that her offspring then use to obtain food as
they grow. The mites also add to the feeding sign
of mite faeces on the hind end of the pupa.
Usually only 4-5 of the eggs that are laid (1 male
and 3-4 females) have time to hatch and complete
their development before the bee is ready to
emerge. The new generation of mites mate in the
cell before the host bee hatches. Only mature
female mites survive to leave the cell when the
bee emerges (figure 2.6). Males and juvenile
Figure 2.3 Varroa life cycle (clockwise from top).
Step 1 – varroa mites are transferred to new
colonies on adult bees. Step 2 – the mite then
leaves the adult and crawls into a brood cell.
Step 3 – once in the cell, the mite submerges
itself in the larval food at the bottom of the cell.
Step 4 – when the cell is capped, the mite
leaves the larval food and starts feeding on the
prepupa. Step 5 – the mite then lays eggs,
which hatch and go through two juvenile stages
before taking on the adult body shape. Step 6 –
the adult mites leave the cell when the bee
emerges. The mites are then transported on
adult bees until they enter another brood cell.
BIOLOGY
Varroa Life Cycle
1
2
3
4
5
6
15
females die in the cell. Some female mites can produce more than one generation by
invading a second brood cell, and small numbers are even able to invade a third cell.
Since not all the new females survive, the
reproduction rate is usually only about 1.3 new
mature female mites per mother mite in worker
cells and 2.6 in drone cells. This rate of
reproduction decreases if more female mites invade
each cell.
Figure 2.6 Juvenile (white) and adult (brown) varroa mites
feeding on a bee prior to emergence. The bee has been
removed from its cell for this picture.
CONTROL OF VARROA: VARROA BIOLOGY
Varroa prefer drone brood.
BIOLOGY
16
3. EFFECTS OF VARROA
This chapter explains the effects of varroa on brood, adult bees, and honey bee
colonies. The chapter includes a description of parasitic mite syndrome.
3.1 Effects on bees
The effects of varroa on adult bees come about either:
• from the mite feeding directly on the haemolymph (blood) of the adult bee; or
• as a result of feeding by the mother mite and her offspring on bee larvae or pupae
in the cell, and the subsequent effect this feeding has on the development of the
pupae into adults.
3.1.1 Effects of varroa feeding on adult bees
Effects stemming from mites feeding on adult bees can include:
• Consumption of haemolymph – An individual mite consumes about 0.2 microlitres of
bee haemolymph during its life. However, this blood loss doesn’t appear to have a
direct negative effect on an otherwise healthy bee.
• Changes in the haemolymph – (see also 3.1.2). There appear to be some changes in
the immune components of haemolymph in bees fed on by varroa. The reason is
unknown, although it may be due to the reduction in the amount of haemolymph
or the reaction of the bee’s immune system to the hole made where the mite
feeds.
• Introduction of viruses – (see also 3.1.2). Acute paralysis virus (APV) is normally
not thought to cause disease symptoms in bees (i.e., it is ‘inapparent’), but there
are suggestions that the virus can increase in bees when it enters their
haemolymph as part of the varroa feeding process. It is also believed that bees
with high levels of APV can then pass on the virus to other adult bees and larvae
through food exchange and feeding. APV appears to kill adult bees in varroainfested
colonies, as well as larvae fed by nurse bees with high levels of APV
caused by varroa.
Increased levels of chronic paralysis virus (CPV) have been found in bees infested
with varroa. CPV can also produce disease symptoms (crawling, shaking, ‘hairless
black’ coloration caused by bees pulling at the hairs of the diseased bee) in bees
that are not infested with varroa.
In the laboratory, Kashmir bee virus (KBV), like APV and CPV, has been shown to
cause death in bees from injection, and it is speculated that KBV may be spread
by varroa. KBV and APV are very closely related viruses. Other viruses also appear
to have associations with varroa (e.g., slow paralysis virus, deformed wing virus,
cloudy wing virus).
Bee viruses known to be present in New Zealand include sacbrood, chronic bee
paralysis, acute bee paralysis, Kashmir bee virus, black queen cell virus, bee virus
X, bee virus Y, cloudy wing virus and filamentous virus. Not all of these are likely
to become associated with varroa.
Varroa can seriously affect adult bees by introducing viruses into
the bees’ blood.
EFFECTS
17
3.1.2 Effects of varroa feeding on honey bee larvae or pupae
Varroa feeding on honey bee larvae or pupae can have several effects:
• Decreased body weight of adults – The greater the number of mites in a cell with a
pupa, the lower the weight of the emerging adult bee and the bee at 6 days old.
Those with 1-3 mites weighed 10% less than uninfested pupae, and those with
more than 3 mites weighed 22% less. Worker bees suffer greater weight loss from
varroa than drones (drones had only a 7% weight loss in one study).
• Deformed wings and abdomens – The number of bees with deformed wings and
abdomens increases with the number of mites on the pupa (figure 3.1). However,
some studies have shown low wing deformity even when mite levels are very high,
and deformed wings can also be caused by a virus. (See also Introduction of
viruses below.)
• Smaller hypopharyngeal glands – Hypopharyngeal
glands are partly responsible for producing royal
jelly. Pupae with 1-3 mites had 13% smaller
hypopharyngeal glands as adult bees, and those
with more than 3 mites had 31% smaller glands.
• Loss of protein in the haemolymph – A study showed
that protein in the bee’s blood decreased as the
number of mites on the pupa increased, with a
27% reduction for 1-3 mites and up to 50% with
more than 3 mites.
• Introduction of viruses – Mites have been shown in laboratory studies to be able to
transfer acute paralysis virus (APV) and other viruses to pupae. Deformed wing
virus (DWV) has been found in pupae infested with varroa and also in non-infested
pupae. However, not all deformed wings in varroa-infested pupae are caused by
DWV, and pupae with high levels of DWV also often do not display deformed wings.
Mites are able to transfer DWV from an infected pupa to a non-infected pupa.
• Reduced emergence rates of drones – Drone brood is 8 to 10 times more likely to be
parasitised by varroa than worker brood, and the effects on drone brood can be
much more severe. In one study, while the amounts of drone brood produced in
both types of colonies were similar, significantly fewer drones from varroa-infested
colonies were alive after one day (60%) compared to non-infested colonies (97%).
In another study, the figures were 65% alive for non-infested pupae, 37% for
pupae with 1-3 mites, and 23% for pupae with more than 3 mites. A large
percentage of surviving drones from infested pupae could not fly, although they
looked normal (57-64% non-flying compared with 5% in non-infested pupae).
• Changes in drone physiology – Slight changes have been recorded for sperm amount
and sexual gland weights in drones from varroa-infested colonies, although in a
study of drones developing from non-infested pupae, and those with 1-3 mites and
more than 3 mites, the figures were more significant (i.e., 8.8 million sperm for
non-infested compared with 5.3 and 4.3 million for the two infestation rates).
• Drone flight times and ability to mate – No significant difference between infested
and non-infested colonies was found in drone flight times and duration of flights,
as well as the ratio of sperm in queens from drones from the two types of colonies.
CONTROL OF VARROA: EFFECTS OF VARROA
Figure 3.1 A bee with deformed
wings caused by varroa previously
feeding on the bee in the brood
Drones suffer the most significant effects from varroa infestation.
EFFECTS
18
So it would appear that drones from infested colonies that do survive and mate are
fully functional, and that queens ensure their mating requirements are met on the
basis of total sperm amount received, not the number of drones they mate with.
• Changes in the age foraging begins – One study showed foraging began at 7 days old
with varroa infested bees compared to 12 days old for uninfested bees, although
other studies showed no difference in the age foraging begins.
• Difference in return to hives following orientation flights – 20% of bees from noninfested
colonies did not return, whereas 36% of bees from infested colonies did
not return.
• Reduction of lifespan of workers – Adult bees developing from uninfested pupae live
longer, with 1/3 of these bees still alive after 35 days, compared to 8% for bees
coming from infested pupae. However, the reduction appears to be related to the
time of year. One study showed a big difference in lifespan towards the end of
summer (when there is a greater natural die-off of bees), whereas at the beginning
of summer there was no significant difference. As well, no correlation has been
found between differences in bee weight and lifespan of bees coming from infested
pupae, or between the protein content at emergence and lifespan. The lack of
correlation suggests a more important influence may be viruses such as APV,
although a range of other factors may also come into play.
• Reduction of lifespan of drones – The difference in emergence rates for drones (see
above) continues over the rest of their lifespan, with about 50% of drones from
non-infected colonies remaining between 5 and 11 days, compared with about
30% for drones from infected colonies. At 12 to 18 days, the figures drop to 37%
and 20% respectively.
• Reduction in foraging – Some studies have shown less flights of shorter duration for
bees coming from infested pupae, resulting in less total foraging time. Other
studies have shown no difference in frequency and duration.
• Reduced wax secretion – Abnormalities have been found in the wax secretion of bees
coming from infested pupae, although little research has been done in this area.
• Reduced tolerance to pesticides – Bees from infested pupae showed less tolerance to
two common pesticides (endosulfan and coumaphos). This is thought to be due to
reduced weight of fat bodies in these bees compared to bees from non-infested
pupae. A bee’s fat bodies can absorb and neutralise the effects of small amounts
of pesticides.
CONTROL OF VARROA: EFFECTS OF VARROA
3.2 Effects on colonies
Taken together, the effects on individual bees can result in a rapid reduction in the
number of adult bees in the hive, abnormal brood, robbing of the colony and/or
absconding of the bees. The final outcome, unless treatment is used to reduce the
population of the mites, is usually colony death.
However, caution is needed when using research results on the effects of the mite on
individual bees to make predictions about honey bee colonies as a whole. Studies have
Honey bee colonies will die from varroa infestation unless treatment is
used to reduce the population of mites.
Varroa can reduce the lifespan of worker bees.
EFFECTS
19
shown that the lifespans of adult bees infested as pupae are not always reduced, which
suggests to some observers that the mite itself is not the only (or even major) reason for
these negative effects. Other factors suggested include climate, food sources and
secondary infections of other diseases. It is also important to consider the build-up in both
mite populations and honey bee populations in a colony (see 3.2.3 Effects on colony
production below).
CONTROL OF VARROA: EFFECTS OF VARROA
3.2.1 Effects on feral colonies
It is commonly assumed that if a honey bee colony infested with varroa is left untreated,
it will eventually die. This is because varroa was originally a parasite of Apis cerana and
it is said that A. mellifera has so far not developed sufficient defences to the mite
through natural or human-assisted selection to survive infestation.
Feral colonies are the most likely to succumb since they are by definition not managed
by humans and treated to control mites. A study carried out in California tracked the
survival of feral colonies both before and after the introduction of varroa. In 1990, 208
colonies were tested and none had varroa. By 1993, 75% of the colonies no longer
existed and all remaining colonies had varroa. On average, varroa was shown to reduce
the life span of feral colonies to between 6 months and 1 year. Interestingly, the mite
was found more widely spread in feral colonies in areas where there was substantial
commercial beekeeping, suggesting managed colonies were a major source of infection
back to the ferals.
A similar study in Arizona showed a somewhat different picture, however. Feral colony
losses increased dramatically in the early 1990s, but this appeared to be caused by
tracheal mite rather than varroa. In 1996, all but two of the feral colonies had varroa,
and the population went from 155 in the summer of 1995 to 12 in spring 1996. The
population then increased again to 59 in the summer, falling back to 22 in spring 1997.
The re-establishment of ferals the next spring shows that feral colony populations are
never static. We can assume that even in areas where varroa is widespread, managed
colonies will still produce swarms each spring that will take up nest sites.
3.2.2 Parasitic mite syndrome
‘Parasitic mite syndrome’ is a name given to a range of abnormal brood symptoms that
began to be noticed by beekeepers and the US Department of Agriculture Bee Research
Laboratory in the mid-1990s. The symptoms were found in association with infections of
both varroa and tracheal mite. Parasitic mite syndrome has also been found in varroainfested
colonies in New Zealand.
Important points to note about parasitic mite syndrome:
• Affects both brood and adult bees.
• May be associated with colony collapse.
Varroa infestation results in the loss of many feral colonies, although the
population of feral colonies is always being renewed from managed colonies.
The effects of varroa on individual bees do not necessarily translate to
similar effects on the colony as a whole.
EFFECTS
20
• Symptoms can appear at any time of the year, although they are more prevalent in
mid-summer and autumn.
• Not all symptoms described below are necessarily present in a colony that has the
syndrome.
Adult symptoms of parasitic mite syndrome include:
• Presence of varroa in the colony.
• Reduction in colony population.
• Crawling bees leaving the hive.
• Supersedure of the queen.
Brood symptoms of parasitic mite syndrome include:
• Presence of varroa on pupae.
• Typical brood symptoms for American foulbrood (AFB), sacbrood and/or European
foulbrood (EFB) (Note: EFB has not been found in New Zealand, but a condition
resembling EFB called half-moon syndrome is sometimes present in colonies).
• Symptoms can sometimes disappear if the colony is fed with the antibiotic
oxytetracycline or sugar syrup, or if Apistan strips are used (Note: feeding
oxytetracycline to honey bee colonies is not permitted in New Zealand).
• The age of brood affected by the syndrome can vary from larvae ‘c-shaped’ in the
bottom of the cell through to prepupae (larvae lying out along the side of the cell).
• Affected brood can be found anywhere on the comb.
• Larvae can be:
- twisted up the side of the cell (this is also a symptom of EFB and half-moon
syndrome) (figure 3.2);
- molten/slumped down in the bottom or along the side of the cell (this is also a
symptom of sacbrood);
- light brown, grey or black in colour.
• Larvae can look like the early stages of AFB (light brown in colour, slumped down
along the side of the cell), but do not rope out when a stick is inserted into a larva
and then slowly removed.
• Scales (dried down larval remains along the side of the cell) can be formed, but
they are soft and can be easily removed. AFB scales are brittle and stick strongly
to the side of the cell.
• The larvae do not have any particular smell.
Parasitic mite syndrome is a sign of heavy varroa infestation.
Figure 3.2 Parasitic mite syndrome
(discolored cells).
Larvae affected by parasitic mite syndrome have
been analysed for various bacteria and fungi, but
no specific causative organism has been found
and no bacterial type is dominant.
It has also been speculated that parasitic mite
syndrome is caused by acute paralysis virus
(APV), with varroa injecting the virus into adults,
where it builds up to lethal proportions and where
the virus is also passed on by infected adults to
the brood by feeding.
CONTROL OF VARROA: EFFECTS OF VARROA
EFFECTS
21
However, the USDA has analysed samples of adult bees from colonies with parasitic mite
syndrome and has found that in a majority of the cases neither APV, Kashmir bee virus
(KBV), nor any of 9 other bee viruses were found. Their conclusion is that while these
viruses may be one of the causes of the syndrome, other factors cannot be ruled out.
CONTROL OF VARROA: EFFECTS OF VARROA
The finding of larvae twisted in a half-moon shape along the side of the cell is quite
similar to both half-moon syndrome found in New Zealand and the symptoms of EFB,
which is not present in New Zealand. There is a suggestion that in all three cases the
common cause of the symptom may be starvation of the larva.
It is known that the causative bacterium of EFB competes with the larva for nutrients in
the larval gut, and it is suggested that the larva moving in the cell in search of food
causes the twisting. It is possible that a lack of nurse bees and proper feeding in a colony
with parasitic mite syndrome may lead to similar behaviour on the part of the larva.
The large number of both adult bees and larvae affected by parasitic mite syndrome
certainly suggest it is caused by a communicable disease. Researchers do not understand
why drugs used to control brood disease or the feeding of sugar syrup can alleviate
symptoms, but the positive effects that result from the use of Apistan certainly suggest a
strong link with varroa.
The larval symptoms of parasitic mite syndrome are likely to cause problems when
attempting to make a field diagnosis of AFB. Microscopic diagnosis is also not
recommended, since some of the many bacteria found in larval samples of the syndrome
closely resemble AFB spores. It is therefore important to carry out a laboratory culture test
on suspect larval samples to make a definitive diagnosis of AFB.
The twisted half-moon shape of larvae also complicates making a diagnosis between EFB,
half-moon syndrome and parasitic mite syndrome. In all cases, larval samples should be
taken and sent to a bee disease laboratory for examination.
It is important to get a laboratory diagnosis when half-moon shaped
larvae are found in a hive.
The presence of parasitic mite syndrome in a hive can make the
diagnosis of other brood diseases such as AFB very difficult.
It is still unclear what actually causes parasitic mite syndrome.
EFFECTS
3.2.3 Effects on colony production
It seems a contradiction that while varroa can have such a wide range of significant
effects on individual bees, and while both parasitic mite syndrome and colony collapse
are the normal fate of most varroa-infested honey bee colonies unless treatment is carried
out, major reductions in honey production are not usually recorded as an early effect of
the pest.
The reason is that the population of mites builds up in a colony over time, and in the
initial stages of infestation mite numbers are not high enough to significantly affect
colony productivity. Rapid colony development in the spring and summer can ‘out-breed’
the mite, and with large numbers of unaffected foragers, infested colonies can produce
normal honey yields.
22
However, with the natural decline in both brood and bee population in a colony going into
autumn, the existing population of mites is likely to infest a greater proportion of the
brood. At the same time, more mites are likely to enter individual brood cells. The mite
level in the colony can also drastically increase suddenly as a result of invasion from
outside (both from robbing of heavily infested colonies and as the result of the transfer of
infested bees from these colonies).
At this time of the year, even a few weeks can see the emergence of a large number of
young bees that have suffered significantly from the effects of the varroa’s feeding. The
bees are unable to carry out normal hive activities, robbing can occur, and the colony
suddenly collapses.
Unfortunately, the production of honey crops by varroa-infested colonies can lull the
beekeeper into thinking infestations are not severe, even though the same colonies can
collapse in autumn after the honey has been produced.
CONTROL OF VARROA: EFFECTS OF VARROA
Varroa can be present in a honey bee colony without producing
noticeable effects, but can then cause the sudden collapse of the
colony, especially in autumn.
Studies investigating the effects of different levels of varroa infestation on honey
production provide conflicting results. Researchers compared honey bee colonies from
eastern Russia that had an average varroa infestation rate of 7% of worker brood 15
months after Apistan treatment, to US colonies with a 33% infestation rate 12 months
after treatment. Honey production in the year following the treatment was nearly identical
in the two groups of hives. In Canada, on the other hand, a study showed that mite
infestation levels of 3-7% of brood in early spring resulted in significantly less honey
production. Another Canadian study found there was no difference in honey production
between colonies treated with Apistan and those not treated. In Austria a study found no
significant differences in honey production between colonies with significantly different
mite infestation rates, and a breeding programme in Germany found lower spring honey
production in colonies with less mites, but similar levels of summer honey production
regardless of mite level.
3.2.4 Effects on numbers of managed colonies
Varroa has been identified as the cause of significant losses of managed colonies in a
number of areas of the world. The losses are usually in the late autumn, or more generally
over winter. However, winter losses from varroa are not easy to isolate from ‘normal’ losses
caused by starvation or other diseases such as tracheal mite.
In 1995-96, thousands of managed honey bee colonies died in parts of the United
States. The die-off was partly due to the long winter and poor spring, but beekeepers who
didn’t treat colonies for mites in the state of Pennsylvania reported losing about 30%
more colonies than those who did treat. A previous study in the state showed 11% overwintering
losses in uninfested operations and 31% in operations with varroa.
A three-year study on mite-infested hives in Wisconsin showed over-winter losses of 29 to
45%. Colonies that were treated twice per year had a better survival rate than colonies
treated once a year. At the same time, a survey in Ontario showed only 20% winter losses
in the 1995-96 winter, and winter losses of infested hives the next year of 10% with
EFFECTS
23
another 2% considered too weak to manage the next spring. Most beekeepers in this
study treated their hives for varroa. A study in Indiana showed beekeepers who treated
their hives for varroa lost between 30% and 50% fewer colonies over winter than those
who did not.
The question is often asked, if beekeepers experience such major losses due to varroa,
why doesn’t this have a dramatic impact on hive number and honey production statistics?
The answer would appear to be that commercial beekeepers normally have to replace
winter hive losses and have well-developed management techniques (splits, nucs,
packages) for this purpose. They have generally been able to use these same practices to
overcome increased winter losses due to varroa, though obviously at greater expense. At
the same time, varroa has lead to many hobbyists giving up beekeeping, although because
they have few hives the impact on total hive numbers is not significant.
CONTROL OF VARROA: EFFECTS OF VARROA
Hive losses from varroa certainly occur, but they are often made up
for by splitting surviving hives the next spring.
Varroa has also required an improvement in overall beekeeping management and forced
beekeepers to become more efficient. Because of varroa, beekeeping is certainly not as
easy as it once was in many parts of the world, and some commercial operators have left
beekeeping because of the management changes required.
3.3 Effects on pollination
Few scientific studies have investigated the impact of varroa on pollination. There is no
doubt, however, that the number of feral colonies has declined in areas where varroa has
become established, and this has reduced background (unpaid) pollination of home
gardens and some crops.
It is also well known that prices for rental of hives used in pollination of commercial crops
increased in the United States in the 1990s. The reason given was the decline in colonies
available for this purpose, particularly in the early spring, with varroa and tracheal mite
both being blamed.
In 1998, 1400 colonies used in commercial pollination in the early spring in California
were surveyed. The sample represented 112 beekeepers from 19 states. About 25% of
the beekeepers had infested colonies, and for those that did, just under 50% of the
colonies were infested. Half of the beekeepers also had Apistan treatments in the
colonies. The study showed that in general the colonies were in good condition.
If effective varroa control measures and pollination hive standards are used, hives used
for paid pollination should provide a good level of service.
EFFECTS
24
4. VARROA POPULATION GROWTH
This chapter describes the link between varroa reproduction and population growth,
and explains why population growth rates are the key to understanding both how
varroa affects honey bee colonies and how the mite can be controlled.
4.1 Reproduction rates
Chapter 2 explained the varroa reproduction process and how not all new female mites
survive to reproduce (in other words, the ‘reproduction rate’). The reproduction rate is
influenced by whether reproduction takes place in a worker or a drone cell, how much
brood is present, and also how many mated females enter a cell.
Small changes in the rate of reproduction have large effects on mite population growth.
Over a 4 month breeding period, a single mite can potentially result in 6 female mites at
a reproduction rate of 1.2 mites per brood cycle, 200 mites at a rate of 1.7 per cycle, and
20,000 mites at a rate of 2.7 per cycle. The reproduction rate is much higher on drone
brood, and therefore mite numbers can increase more rapidly when it is present.
Mite numbers can increase more rapidly when drone brood is present.
Mite numbers in a hive will decrease when there is no brood present.
Since varroa needs brood to reproduce, and since it reproduces more successfully on
drone brood, the amount and type of brood present in a colony will have a large impact on
mite population growth. In situations where there is no brood rearing in colonies, mite
populations cannot increase. Mites die and get lost outside the colony. The longer a
colony is broodless, the greater will be the reduction in mite numbers.
Mite numbers will, however, increase again as soon as there is brood (slowly when there is
only worker brood, and faster when there is also drone brood). Varroa populations
therefore increase faster in climates that support brood rearing all year round and drone
rearing for most of the season.
4.2 Understanding varroa population growth
In order to decide how frequently colonies should be treated for varroa, it is important to
have some understanding of the speed of varroa population growth. The population of
varroa inside a colony can increase as the result of:
• varroa reproduction inside the colony; and,
• the invasion of mites from other colonies.
4.2.1 Reproduction and population growth
Varroa can reproduce only when there is capped brood in a colony. The mite reproduction
rate is also much higher on drone brood than on worker brood. Because in New Zealand
the amount and type of brood varies with the season and the location, we should expect
varroa population growth rates to also vary considerably.
Varroa populations increase faster in climate areas that support brood
rearing all year round.
POPULATION GROWTH
25
In the winter in locations where there is no brood present, the only mites will be those
carried on adult bees. During this time, the number of varroa in a colony will decrease as
varroa die, drop to the floor board, get lost outside, or are carried out on dead or sick
bees. It has been calculated that varroa can survive on bees without brood for between 80
and 100 days, although longer survival times have been suggested. About 10% of the
original mite population present when brood-rearing stops will die each month that the
colony remains broodless.
Figure 4.1 Theoretical population growth curve for varroa during the summer when it is reproducing on
worker brood and drone brood.
CONTROL OF VARROA: VARROA POPULATION GROWTH
About 10% of the original mite population present at the end of
brood-rearing will die each month that the colony remains broodless.
When varroa reproduces, the population grows ‘exponentially’. What this means is that the
number of varroa within the colony will increase very slowly at first, and then more and
more quickly as times goes on. The blue line in figure 4.1 shows how varroa populations
increase when the mite reproduces on worker brood. In this theoretical example, mite
numbers increase from 1 mite to 11 in the first 50 days. In the second 50 days the
population increases by a further 115 mites, and by 1330 mites in the next 50 days.
Varroa populations increase ‘exponentially’ when not limited by the
amount of brood.
The growth curves will eventually slow down when the amount of brood in the colony
becomes a limiting factor. As the number of varroa in each cell increases, their ability to
reproduce decreases. However, by this time the mite infestation will be causing serious
damage to the colony.
Since varroa show a preference for drone brood and can breed more successfully on it, the
population will grow much faster if drone brood is present (purple line in figure 4.1).
Where one mite results in a population of 1456 mites after 150 days on worker brood,
over the same time period the mite population would be 6000 mites if they reproduced
exclusively on drone brood.
POPULATION GROWTH
2000
4000
3500
3000
500
1000
1500
4500
2500
0
1 22 43 64 85 106 127
Worker brood
Drone brood
Varroa
Days
26
Since varroa reproduction rates are higher on drone brood, varroa populations increase
much faster when drone brood is present in a colony.
4.2.2 Invasion and population growth
Beekeepers spread varroa by transferring queens, combining colonies, swapping frames of
brood between colonies, and transporting inadequately screened hives and boxes of honey.
The spread of varroa around the world has been greatly assisted by humans moving honey
bees from place to place.
Varroa can also enter a honey bee colony in a number of other ways. Probably the most
common is through worker bees and drones drifting between colonies. Worker bees
frequently drift between colonies in the same apiary and between apiaries. Drones also
drift, although not as far as is often believed. The varroa carried by drifting workers and
drones leave the bees and infest the brood of the new colony.
Varroa is also spread by worker bees robbing colonies weakened by varroa. The mites
attach themselves to the robbing bees and then infest the robbing colony when the bees
return from their robbing foray.
The main sources of ‘invasion’ of mites into other colonies are through drifting and
robbing. Even though a colony may only be invaded by a few mites per day, their invasion
can have a huge effect on varroa numbers because of the mites’ exponential growth rate.
Two mites invading a colony per day can result in the varroa population in a colony
reaching 1000 mites a month earlier than if no invasion had taken place (figure 4.2).
Figure 4.2 Theoretical population growth curve for varroa during the summer when it is reproducing on
worker brood and 0, 1 or 2 varroa are invading the colony each day.
CONTROL OF VARROA: VARROA POPULATION GROWTH
Varroa
Days
500
900
800
700
200
300
400
1000
600
0
1 22 43 64 85 106 127
0 varroa/day
1 varroa/day
100
2 varroa/day
Even low invasion rates can greatly increase the varroa population
growth rate within a colony.
POPULATION GROWTH
27
A single large invasion of varroa can also have a major influence on the population growth
rate. For example, in an infestation starting with 1 mite, an invasion of 50 mites on day 10
can halve the amount of time it takes for the population to reach 1000 mites (figure 4.3).
Figure 4.3 Theoretical population growth curve for varroa during the summer when it is reproducing on
worker brood and 50 varroa invade the colony on day 10.
A study in Italy showed just how high invasion rates can be. The invasion rate was low
during the spring, increased to between 1.6 and 13.7 mites per day during summer, and
reached a peak of 75.6 mites per day during early autumn.
CONTROL OF VARROA: VARROA POPULATION GROWTH
Varroa
Days
500
900
800
700
200
300
400
1000
600
0
1 22 43 64 85 106 127
Natural growth
+ 50 varroa
100
A small number of varroa invading a colony on one day can greatly
increase the population growth rate of the mite.
4.2.3 Acute versus chronic infestation
Figure 4.3 also explains why varroa infestations often appear more severe (the ‘acute’
stage) when varroa first comes into an area, and then settle down several years later to a
more predictable pattern requiring routine control (‘chronic’ stage).
In areas where there are large numbers of feral colonies or untreated hives, these colonies
act as a major source of mite invasion when they become sufficiently weakened by
infestation that they are robbed by managed hives. Mite populations in these managed
hives can increase dramatically, with the mites that are transferred to these hives greatly
increasing the population growth curve. It is therefore very important in the period
following varroa coming to an area to treat hives on a routine basis (especially in the
autumn). The chemical treatment will guard against unpredictable increases in mite
population that can lead to substantial hive losses.
During the acute phase, it is very important to carry out varroa control
treatments on a routine basis, especially in autumn.
POPULATION GROWTH
28
Varroa
Days
800
1400
1200
400
600
1000
0
1 22 43 64 85 106 127
99% kill rate
90% kill rate
200
148 169 190 211 232
80% kill rate
4.2.4 Effects of control on population growth rates
The effectiveness of a control method can also have a large influence on mite
populations because of the exponential growth rate of varroa. Using a control method that
kills only 80 or 90% of mites, rather than 100%, may seem adequate. However, even
small differences in the percentage of surviving mites can have a large effect on how
soon the varroa population in a colony will reach high levels again. In the example in
figure 4.4, where control measures are used when mite levels reach 1000 mites, with
99% control it will take 94 days for varroa population levels to reach 1000 again, and
only 48 and 35 days respectively with control measures that are 90% and 80% effective
(assuming no re-invasion).
Figure 4.4 Theoretical population growth curve for varroa when it is reproducing on worker brood, there is
no re-invasion, and a control method is used on day 144 that is either 99, 90 or 80% efficient.
CONTROL OF VARROA: VARROA POPULATION GROWTH
Small variations in the effectiveness of a control method can have a large
effect on how soon varroa populations will reach damaging levels again.
Some control measures work on the principle of making small reductions in mite numbers
on a daily basis. However, when such measures are analysed using population growth
curves, it is evident that they may not have a significant effect on keeping mite
population levels below economic thresholds. For instance, a method that on a daily basis
removes 15% of mites per year will have little effect on mite population growth.
Nevertheless, a combination of methods that each reduce varroa by a small amount may
possibly act together to provide adequate control.
A control measure that only removes a small number of varroa throughout
the year may by itself have little effect on how quickly varroa populations
reach damaging levels.
POPULATION GROWTH
29
5. DETECTION AND EVALUATION OF INFESTATIONS
This chapter describes how beekeepers can sample their hives for varroa, and how
they can use the results of the sampling to determine the likely population of mites in
individual hives.
5.1 Why sample hives for varroa
Beekeepers need to detect and evaluate infestations of varroa for four important reasons:
• Surveillance in the South Island Disease Free Area – while the government is carrying
out an extensive ‘active’ surveillance programme to verify the varroa-free status of
the South Island, beekeepers need to play their part by looking for the mite on an
on-going basis. This type of surveillance is called ‘passive’ surveillance, and it is
essential to ensure that any incursion of the mite is found early enough so that an
eradication or containment operation can be contemplated. Because varroa is not
easily seen until it has built up to large populations in the hive and is causing
direct colony effects, beekeepers throughout the South Island should use simple
detection techniques at least twice per year (spring and autumn) to search for the
mite. Sampling brood with a cappings scratcher (see 5.3.3) can be done whenever
hives are inspected.
• Surveillance in North Island areas not known to have varroa – the best way
beekeepers in the North Island can prepare themselves for the impact of varroa is
to carry out on-going passive surveillance in areas not known to have the mite.
Again, because varroa is not easily seen until it causes direct colony effects,
beekeepers need to know when the mite actually reaches their area so they can
begin proper control programmes. In these areas, beekeepers should also use
simple detection techniques at least twice per year (spring and autumn), and
brood sampling whenever hives are inspected.
• Determining when to treat hives for varroa (thresholds) – once varroa has arrived in an
area and the acute (high invasion) period has passed, beekeepers need to know
how quickly varroa is building up in their hives and when to apply treatments.
Simple detection techniques can be used, particularly in the spring and autumn,
to determine if mite population levels have reached economic thresholds that
require treatment. This type of evaluation is an important part of integrated pest
management (IPM) programmes designed to reduce the frequency and costs of
treatments. See chapter 10 for more information on IPM programmes.
• Determining the effectiveness of treatments – just because a treatment has been
given to hives doesn’t necessarily mean it has been effective. Simple detection
techniques can be used to determine the number of remaining mites in the hive
and whether further treatment is necessary. This type of evaluation is particularly
important in control programmes using biotechnical methods or organic miticides.
It is also useful to help identify if varroa has developed resistance to a particular
control compound.
All beekeepers in New Zealand should routinely check their hives for
varroa whether or not mites have already been found in their area.
5.2 Identifying varroa
To detect varroa and evaluate its population in hives, it is important to be able to identify
the mite and tell it apart from other objects of similar size and shape.
DETECTION &
EVALUATION
30
Varroa is oval in shape and in the adult form is reddish brown to dark brown in colour.
Immature stages (normally only found on pupae) are light brown to off-white. A mature
female varroa measures 1.6mm from side to side, and 1.1mm from front to rear. Mature
males are smaller, but are usually only found on pupae.
CONTROL OF VARROA: DETECTION AND EVALUATION OF INFESTATIONS
Figure 5.1
Comparison
between varroa
(top) and
melittiphis
(bottom).
Varroa can be mistaken for the melittiphis mite, although melittiphis is
smaller and different in shape.
In New Zealand varroa can sometimes be mistaken for Melittiphis alvearius, a mite often
seen running quickly on the top bars of hives particularly just after the hive mat is
removed. Melittiphis is not a parasite of honey bees. It is thought to be either a scavenger
of pollen and hive debris or a predator of tiny pollen mites that also live in beehives.
Melittiphis is about one quarter the size of varroa, and is different in shape. It does,
however, tend to be quite similar in colour to varroa (figure 5.1).
Figure 5.2 Varroa
mites spread
amongst hive
debris on a
bottom board.
The larger yellow
object in the
foreground is a
pollen pellet.
Varroa can also sometimes be mistaken for bits of hive debris (figure 5.2), and dark brown
flecks from the sides of cells on older brood comb or small pieces of propolis. It is
important to check these flecks by picking at them with a sharp corner of the hive tool or
with forceps. The flecks will usually be quite irregular in shape, whereas varroa is smooth
and rounded, and if the mite is turned over and examined closely legs will be obvious.
5.3 Detection methods
There are a wide range of varroa detection methods, with at least one new method (the
sugar shake) having been developed quite recently. All the methods have their advantages
and disadvantages, and some are more accurate than others. It is important to pick a
method that fits with beekeeping workloads and also provides the sort of information
needed to make good decisions.
There are a number of important factors to be considered when deciding on which mite
detection method to use, including:
• cost per hive;
• length of time required to process a sample;
• number of visits needed to the apiary;
• ability of the method to detect low mite numbers (sensitivity); and
• ability of the method to reliably determine the number of mites in a hive.
Choose a varroa detection method that fits with your workload and the
sort of information you need to make good decisions.
DETECTION &
EVALUATION
31
For each detection method, these factors have been summarised in Table 5.1.
Table 5.1 Summary of detection methods
Method Section Cost Test time Total time Visits Sensitivity Reliability
Bees - visual 5.3.2 nil 1 min 2 min 1 very low very low
Drone brood 5.3.3 nil 5 min 5 min 1 high low
Ether roll 5.3.4 low 5 min 5 min 1 low medium
Washing 5.3.5 low 5 min 5 min 1 high high
Sugar shake 5.3.6 low 5 min 5 min 1 high high
Smoke 5.3.7 moderate 5 min 30 min 1 low low
Mesh boards 5.3.8 moderate 5 min 24 hrs 2 low high
Miticide 5.3.9 high 2 min 24 hrs 2 very high very high
When determining whether there are mites in an area for the first time, it is important to
use a technique that has the sensitivity to detect very small numbers of mites. On the
other hand, when determining whether or not there are enough varroa to be worth treating,
being able to detect small numbers of mites is not as important as the reliability of the
method to detect mite populations before they reach damaging levels.
In the descriptions of the following sampling methods, information on economic
thresholds is provided from overseas sources where it is exists. However, we do not yet
know how fast varroa reproduces in New Zealand. Also, the thresholds do not relate to the
acute stage when mite invasion is a problem. As a result, the information below on
reproduction rates and thresholds needs to be treated with caution by New Zealand
beekeepers. For more information on economic thresholds, see section 10.3.
CONTROL OF VARROA: DETECTION AND EVALUATION OF INFESTATIONS
5.3.1 Sampling bees
Studies have shown that varroa are not evenly spread throughout the hive, and that the
distribution depends on the time of year. Obviously when there is no brood in the hive, all
the mites are on adult bees, and methods that sample bees can be very accurate at
predicting the total number of mites in the hive.
When there is a large amount of brood in the hive in spring and early summer, however, at
any given time a high percentage of the mites will be in the brood rather than on adult
bees. Conversely, when the brood amount declines in late summer and autumn, large
numbers of mites will be found on adult bees, making it seem as if there is a major
increase in the mite population.
Varroa are twice as likely to be found on adult bees taken from the brood nest compared
with bees taken from honey supers. It has also been shown that to get a good
representation of the number of mites distributed on adult bees, bees have to be taken
from at least three brood frames.
The easiest way to sample bees is to:
• up-turn a hive lid;
• shake the bees from 3 brood frames into the lid (make sure not to include the
queen);
• turn the lid slightly on its side and give it a bump to dislodge the bees;
• scoop the jar along the bottom side of the lid to collect the dislodged bees.
DETECTION &
EVALUATION
Data on varroa reproduction rates and thresholds from overseas should be
treated with caution.
32
5.3.2 Visual inspection of bees
Even though good beekeeping management involves constant examination of bees and
brood for diseases, visual inspection of adult bees is not a recommended method for
varroa detection. This is because mites often crawl between the hard segments of a
bee’s abdomen to feed, leaving only a small portion of the mite exposed. Varroa can also
move fairly quickly from the top of the bee (especially on the thorax) underneath to
where the legs are attached. In this position the mites are much harder to see. It can
even be difficult to see mites when bees are taken out of the hive and carefully
examined individually.
What can be said with certainty is that if significant numbers of mites are detected by
visual inspection, it is a sign that the mite population in the hive is dangerously high
and urgent treatment is required.
CONTROL OF VARROA: DETECTION AND EVALUATION OF INFESTATIONS
Always take an adult bee sample for varroa from at least three brood
frames. Don’t take bee samples from honey supers.
Visual inspection of bees is not a good varroa detection technique.
5.3.3 Visual inspection of brood
This is certainly a more sensitive technique than visual inspection of bees, especially if
drone pupae are examined, since varroa show a preference for reproducing on drone
brood. When brood is sampled, it should always be examined from at least three brood
frames to ensure accuracy of results.
Method – The best tool to use is either a cappings scratcher (used during honey
extraction) or a wide-blade shearing comb mounted on a handle. Push the tines through a
patch of capped drone brood and then lever the tool to pull a large patch of pupae out all
at once (figure 5.3). It takes some getting used to, but if care is taken about 200 pupae
can be pulled out in 10-15 goes. Check the pupae for mites. Mites are easier to see on
pupae at the pink-eye stage than on ones that have taken on adult colouration. Pupae
that are younger than the pink-eye stage tend to be too soft and fall apart when the
scratcher is levered.
It may also be worthwhile banging the comb over a piece of white card once you are
finished removing all the pupae. Varroa that do not come out with the pupae may fall onto
the card. A study showed the cappings scratcher technique to be about 1.5 times more
efficient in detecting mites than the ether roll (see 5.3.4 below), but certainly not as good
as soapy water/alcohol wash or miticide strips (see also 5.3.5 and 5.3.9 below).
Advantages – Sampling drone pupae is better than
either visual examination of bees or the ether roll. It
is also fairly fast compared to some other methods,
and can easily be carried out as part of routine hive
inspection. The method samples mites on brood,
which can give a more accurate picture of infestation
levels during the main beekeeping season than
sampling adult bees.
Disadvantages – Sampling drone pupae destroys
drones that may be needed for queen mating
Figure 5.3 Using a cappings scratcher
to sample drone pupae for varroa.
DETECTION &
EVALUATION
33
(especially if hives are being requeened on site with cells). The method is also not as
reliable as some others. Even though varroa prefer drone brood to worker brood, there are
times in infested colonies when very few varroa can be found on drone brood.
Thresholds – Researchers in Britain have worked out population thresholds for varroa
using the drone brood sampling method. The threshold depends on the number of cells of
drone brood in the colony and the time of year. As an indication, in a colony with 500
cells of drones at the beginning of summer, if more than 10 drone pupae are found to be
infested when 200 pupae are examined, then the mite population could build up to a
level (2500 mites) needing treatment by the following autumn.
CONTROL OF VARROA: DETECTION AND EVALUATION OF INFESTATIONS
Sampling drones with a cappings scratcher can be a worthwhile technique
for finding varroa, although it is not highly reliable in determining mite
population levels.
5.3.4 Ether roll
The ether roll technique is one of the oldest and most popular techniques for
detecting varroa.
Method – Use a 500ml preserving jar with a metal ring. Cut a piece of wire mesh (3mm
openings) in a circle to cover the jar, then friction fit it into the metal ring. Collect about
300 bees in the jar (about 1/3 full) and cover with the ring and mesh. Make sure to take
your bees from at least three brood frames. Spray the bees through the jar with ether from
an aerosol can (sold as engine starter at car parts stores) (figure 5.4). Shake the bees in
the jar for about 30 seconds, then gently rotate the jar 2 or 3 complete turns. The mites
will come off the bees and will stick to the inside glass walls of the jar. Finally, empty the
bees out of the jar and spread them on a piece of white card to expose more mites. If the
jar is going to be used repeatedly for sampling, the contents (bees and mites) should be
removed immediately. Mites can stick to the glass if they are left for any length of time
and this will give you false readings on subsequent hives. (Warning: ether is highly
inflammable, so it should not be used near bee smokers).
Advantages – The ether roll is quick, easy to use,
and can be done in the apiary in one visit. It is
regarded mostly as a means of detecting mites if
they are present at fairly high levels.
Disadvantages – Ether is inflammable and
potentially dangerous. Also, the ether roll may
not give a very accurate estimate of the number
of mites in the hive. A study showed this survey
technique to be only about 78% effective at
removing varroa from bees compared with
Apistan strips placed in hives for only 4 hours,
so it is not a very sensitive technique. Another study showed that very high colony mite
populations can yield low ether roll readings. Finally, it has been shown that not all mites
that are on the bees cling to the inside of the glass container (only 59% in one study).
This can be improved by washing the sample with alcohol or soapy water and then filtering
(see 5.3.5 below). The ability of the test to predict the actual number of mites in the hive
can also be increased by taking several samples from the hive.
Figure 5.4 Spraying bees with ether to
sample them for varroa.
DETECTION &
EVALUATION
34
Thresholds – One source states that if 15 or more mites per 300 bees are recovered from
an ether roll, mite control measures should be carried out. This was based on a detailed
study of mite levels in southeast USA. Another source suggests that if no mites are found
with the ether roll test in autumn once the flow has ended, no varroa treatment needs to
be carried out going into winter. A third source sets the limit at the end of summer at no
more than six mites, with 1-5 mites meaning that treatment can be delayed until late
autumn or next spring.
CONTROL OF VARROA: DETECTION AND EVALUATION OF INFESTATIONS
The ether roll is a quick technique for varroa detection, but it is also not
very accurate in determining mite population levels.
5.3.5 Soapy water or alcohol
Washing adult bees in alcohol was one of the first methods devised for measuring mite
populations in beehives, and it is still one of the most accurate. Alcohol (25%) is often
not available, and is also costly, so a technique has now been devised using soapy water
instead. Methylated spirits (25%) can also be used, but care is needed to avoid breathing
in the fumes.
Method – Mix a level tablespoon of liquid or dry laundry detergent in one litre of water.
Select a detergent that doesn’t foam very much, since foaming can make the procedure
more difficult. Collect 200 or more bees from the brood nest (about 1/4 of a 500 ml jar),
making sure to take bees from at least three brood frames. Put the lid on the jar and
shake the bees and the soapy water for one minute. Expect to remove 80-90% of the
mites in that time period, but it takes a full 30 minutes to free almost all of the mites
(99%). Pour the contents of the jar over a piece of cotton cloth (e.g., a piece torn from an
old bed sheet) placed above a bucket to catch the soapy water (figure 5.5). Count and
carefully remove the bees, then count the number of mites. Finally work out the number
of mites per 100 bees. To save time, you can use a piece of 8 mesh for the lid, as in the
ether roll, and pour the bees and liquid through it. The mesh will collect the bees, but let
the varroa come out with the liquid onto the cloth. Another way to improve accuracy is to
thoroughly wash the bees with a sprayer into a bowl. Use a strong spray and count the
number of mites that float on the top of the water in the bowl.
Advantages – The soapy water/alcohol method is both lowcost
and accurate, and involves only one trip to the apiary.
Disadvantages – The method takes more time than the ether
roll because the contents of the jar have to be filtered.
Thresholds – The same British researchers who worked out
thresholds for varroa populations based on examining drone
brood have also developed thresholds for using the adult
bee washing technique. The threshold depends on the size
of the colony and the time of year. In a colony of 20,000
bees in the winter, if more than one mite is found in 300
bees, the mite population could build up to a level (2500
mites) needing treatment by the following autumn. For a
colony with 60,000 bees at the end of the honey flow, the
threshold number of mites is between two and ten in 300
bees. This threshold is variable since it depends on when
the honey flow ends and the amount of worker brood and
drone brood present in the colony in the preceding weeks.
Figure 5.5 Pouring soapy
water soaked bees over a
piece of cotton cloth
stretched over a bucket.
DETECTION &
EVALUATION
35
5.3.6 Sugar shake
This is a new method developed as a more bee-friendly alternative to the ether roll. The
method doesn’t kill the bees.
Method – Use the same type jar and mesh lid as for the ether roll. Collect about 300 bees
in the jar (about 1/3 full) and add about 1 tablespoon of icing sugar on top of the bees.
Gently roll the sugared bees for 3-5 minutes, ensuring each bee is coated with sugar. Let
the jar sit for a few minutes, then turn the jar upside down and shake the jar above a
piece of paper. The mites and sugar will pass through the mesh, but the bees will remain
in the jar (figure 5.6). The bees won’t be killed, so they can be put back in the hive. If the
sugar makes the mites hard to find, put the sugar through a fine sieve. This will allow the
sugar to escape but the mites will be retained. The mites can then be dumped onto a
piece of paper for counting. Recovery is said to be 70% of mites for a brief shaking. A
study showed 79.8% recovery if the bees are shaken 3 times, or until no more mites fall
out. It is best not to reuse the same icing sugar between hives, since the very fine
particles are the ones that dislodge the mites and these particles cover the bees and also
blow away in the wind.
The reason the sugar works has not been determined, but it may be that either the sugar
interferes with the sticky pads on the legs of the mites that help them cling to the bees,
or the sugar makes the mites stop feeding on the bees and attempt to groom themselves.
Advantages – The sugar shake
method is a simple, quick
technique that doesn’t kill bees. It
also only requires one trip to the
apiary. The method doesn’t produce
chemical residues.
Disadvantages – Although recovery
rates of mites have been suggested,
there are very few published studies verifying them.
Threshold – A US researcher suggests a threshold of 65 mites recovered from 300 bees,
which is similar to an ether roll figure of 15 mites per 300 bees.
The sugar shake method is quick and kind to bees, but there is little information on its
accuracy in determining mite population levels.
5.3.7 Tobacco smoke
This technique has been used in Europe, both as a survey method and as a varroa
treatment.
Method – Light a smoker using your standard smoker fuel. Insert a sticky board through
the hive entrance (see section 5.5). When the smoker is going well, add about 2-3 g of
smoking tobacco (pipe tobacco), which should be enough for 2 hives. Blow 60 strong
puffs into the entrance of the hive at about 1-second intervals. Don’t open the hive for 30
minutes. Mites will fall onto the sticky board. A study showed this technique to be about
twice as efficient in detecting mites as the ether roll.
CONTROL OF VARROA: DETECTION AND EVALUATION OF INFESTATIONS
The soapy water washing technique is an accurate technique for
determining varroa levels in a hive, but it is fairly time-consuming.
Figure 5.6 Sugar shake method of varroa sampling,
including a close-up of mites on a counting card.
DETECTION &
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36
Advantages – The technique uses natural substances (but potentially toxic ones) and
standard beekeeping equipment. It requires only one trip to the apiary.
Disadvantages – Tobacco is costly, and if too much smoke is used the bees in the colony
can drop to the bottom board causing most of the colony to asphyxiate. The technique is
also quite time-consuming.
Thresholds – Unknown.
CONTROL OF VARROA: DETECTION AND EVALUATION OF INFESTATIONS
The tobacco smoke technique is not recommended because it is costly
and can kill a colony if not used properly.
5.3.8 Mesh bottom boards
This method is also being investigated as a control measure for varroa, and is often used
as part of an integrated pest management system for varroa control.
Method – (see section 8.3 for a description of mesh bottom boards). The screen board can
be used either in association with a sticky board, or the bottom board debris can simply
be examined for mites since a certain number fall to the bottom board every day (often
called ‘natural mite fall’). A piece of white plastic (Corflute or similar) is often used to
make the mites easier to see.
British researchers believe that the method is most accurate when a colony has either no
brood or a good-sized brood nest (equivalent to more than 5 frames of brood 60%
covered). The board should stay on for 3-5 days, so that the daily mite fall more
accurately represents the total number of mites in the hive. If the board stays on for a
longer period, the mites may be difficult to count because of debris or total mite fall
(especially during the invasion period). Manipulating the hive once the board is on also
increases the amount of debris on the board.
Make sure to divide the total number of mites on the board by the number of days the
board has been in place. A Canadian researcher has found that 24-hour mite fall
correlates very strongly with total mite population.
Advantages – Mesh bottom boards provide very accurate estimates of mite populations,
and according to some authors they are the best technique for making varroa control
decisions. The method also reduces mite numbers, but does not provide sufficient control
without the addition of other control measures.
Disadvantages – Mesh bottom boards can be expensive to make. For mite sampling, they
also require at least two trips to the apiary.
Threshold – Various European scientists have developed threshold information on natural
mite fall. According to the British team, colony collapse is likely by the end of the season
if the average daily natural mite fall is greater than 0.5 mites/day in winter/early spring,
6 mites/day in spring, 10 mites/day in early summer, 16 mites/day in mid-summer,
33 mites/day in late summer and 20 mites/day in autumn.
According to Danish researchers, control should be undertaken immediately if daily mite
fall is greater than 8 mites/day. For 2 mites/day, control should be undertaken within
2 months, and for 1 mite/day, control should be within 3 months or at least before winter.
All of these figures are for the chronic stage once invasion pressure has reduced.
DETECTION &
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5.3.9 Apistan, Bayvarol and formic acid
These chemicals are used in mite detection and survey work. Apistan or Bayvarol with a
sticky board is the technique of choice for government surveillance programmes in the
South Island Disease Free Area and the North Island Surveillance Area.
Apistan and Bayvarol are highly effective at killing varroa mites, and formic acid is also
effective. However, none of the chemicals are 100% accurate in determining the
presence of mites when varroa is at extremely low levels and most mites are in the brood.
Only the mites on adult bees will be killed by the chemicals, although there is some
suggestion that formic acid also kills mites in sealed brood (see section 6.3.2.1). When a
colony is in full brood rearing, on average only about 15% of the mites are on adults.
Method – For Apistan use two strips per two-box hive, spaced evenly within the cluster of
bees. For Bayvarol use four strips per two-box hive. In either case, remove the strips after
24 hours. For formic acid, apply 40 ml of 65% liquid directly onto a few layers of paper
towels placed together on the top bars of the top brood box. Remove the towels after 2-3
days. Use the miticides with either a sticky board or white card (plastic or similar) on the
bottom board to collect dead mites. Strips can be reused for survey work up to 10 times,
provided each application is only for 24 hours and the strips are kept out of sunlight.
Strips can be marked with an ear-tag pen to indicate how many times they have been
used. When not in use, they should be wrapped in tinfoil and stored in their original box
in a cool, dry place.
Advantages – This method is the most sensitive and reliable at detecting varroa since all
adult bees in the hive are surveyed. The chemicals cause rapid mite fall, although with
formic acid it is necessary to leave the chemical on the hive for longer before counting the
mites, since mite fall is at times not as rapid as for Apistan or Bayvarol. A study
conducted by HortResearch suggests that about 86% of the mites on adult bees will be
killed by either Apistan or Bayvarol in the first 24 hours.
Disadvantages – The method can be expensive, and can even be counter-productive if the
reason for surveying is to determine mite threshold levels to reduce chemical control use.
Two trips to the apiary are required.
Thresholds – One author suggests that in late summer the threshold is 20-200 mites
based on a 24 hour mite fall, whereas in Europe levels as high as 800-1400 mites are
considered to be critical.
CONTROL OF VARROA: DETECTION AND EVALUATION OF INFESTATIONS
Mesh bottom boards are an accurate way to determine mite population
levels, and may offer some mite control.
Apistan, Bayvarol and formic acid are effective detection methods for
varroa surveillance.
5.4 Sticky boards
Sticky boards are used in several survey techniques, and are essential in determining
natural mite fall (figure 5.7). They can either be purchased or made by the beekeeper.
DETECTION &
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38
To make a sticky board, mix 1 part vegetable
oil with 1 part petroleum jelly. Apply over
the surface of a piece of white paper or
cardboard with a paint brush and then
remove the excess with a window squeegee.
Alternatively, spray on cooking oil from an
aerosol can (Pam or similar), or use A4
adhesive labels (Avery or similar) stapled to
the board.
If natural mite fall is being measured
without a mesh bottom board, it is a good
idea to screen the sticky board if it is going
to be left in the hive for any length of time. Unless the board is made of plastic, the bees
will chew the board and affect the results. The screen should be elevated about 8mm
above the board to keep the bees from removing some of the varroa.
It is also important not to reduce the size of the sticky board (for instance, to half size),
since some of the mites will not be collected on the sticky board and this will give a false
impression of the number of mites in the hive.
5.5 Using mite population estimates
Specific threshold levels (where available) for the various sampling methods are
summarised in table 5.2. Total mite populations in hives can also be determined from
these methods by using the calculations presented in appendix 1. It is very important to
note, however, that in the acute stage of varroa infestation, mite population estimates
(especially in the autumn) should not be relied upon to determine whether mite control
treatment should be applied. Invasion pressure can drastically alter the mite population in
a hive in a short period of time. During the acute stage, mite control should always be
carried out in the autumn.
CONTROL OF VARROA: DETECTION AND EVALUATION OF INFESTATIONS
Figure 5.7 A sticky board with a protection screen
to keep the bees from chewing up the cardboard.
In the acute stage of varroa infestation, mite population estimates
(especially in late summer/autumn) should not be relied upon to
determine whether mite control treatment should be applied.
DETECTION &
EVALUATION
39
CONTROL OF VARROA: DETECTION AND EVALUATION OF INFESTATIONS
Table 5.2 Comparison of various mite detection methods.
[Note: the information on threshold levels is based on overseas research and should be treated with caution
under New Zealand conditions. The information also does not take into consideration invasion pressure
during the acute stage.]
Method Time of year Sample size Threshold level Threshold level
comments
Drone brood Early spring 200 drone pupae >10 drone pupae Mite levels
examination infested will rise to 2500 in
hive by autumn
Ether roll – 300 bees >15 mites Carry out treatment
immediately
Autumn 300 bees No mites present No autumn treatment
required
Late summer 300 bees >6 mites Treatment needed
300 bees 1-5 mites Treatment can be
delayed until late
autumn/spring
Soapy water Winter 300 bees >1 mite Treatment needed by
autumn
Late summer 300 bees >2-10 mites, Autumn treatment
depending on when needed
flow ends and brood
Sugar shake – 300 bees >65 mites Carry out treatment
immediately
Tobacco smoke No information
Mesh bottom Winter Daily mite fall >0.5 mites/day Colony collapse likely
boards by end of season
Spring Daily mite fall >6 mites/day Colony collapse likely
by end of season
Early summer Daily mite fall >10 mites/day Colony collapse likely
by end of season
Mid-summer Daily mite fall >16 mites/day Colony collapse likely
by end of season
Late summer Daily mite fall >33 mites/day Colony collapse likely
by end of season
Autumn Daily mite fall >20 mites/day Colony collapse likely
by end of season
Summer Daily mite fall >8 mites/day Begin treatment
immediately
Summer Daily mite fall 2 mites/day Control needed
within 2 months
Summer Daily mite fall 1 mite/day Control needed
within 3 months,
or before winter
Apistan, Bayvarol, Late summer 24 hour mite fall Between 20-200 Begin treatment
formic acid and 800-1400 immediately
depending on study
DETECTION &
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40
6. CHEMICAL CONTROL
This chapter describes the various synthetic and organic chemicals that are used by
beekeepers to control varroa.
6.1 Chemical safety
Various chemicals have demonstrated an ability to control varroa in honey bee colonies
(table 6.1). Although these chemicals can be divided into ‘organic’ (found in nature) and
‘synthetic’ (not found in nature), it is important not to think of organic pesticides as ‘soft’
or ‘safe’ and synthetic pesticides as ‘hard’ or ‘hazardous’. Many organic pesticides are
quite harmful to both bees and beekeepers if used incorrectly.
There is also a tendency to underestimate the risks posed to human health by agricultural
pesticides and chemicals in general. A good example of this comes from the varroa
delimiting survey that was carried out around the country using Apistan. Many people
handled the Apistan strips without gloves despite having been warned of the hazards of
doing so, and despite the label clearly stating that gloves should be worn.
Many of the chemicals used to control varroa are not only toxic to mites; they can also be
toxic to honey bees and humans. In addition, some control chemicals are highly corrosive.
Although we have an idea of the short-term effects of high concentrations of these
chemicals, we can only guess at the impact of many of the compounds when encountered
in low concentrations over long periods of time. All agricultural chemicals should be
considered as toxic to humans unless there is evidence to show that they are not. Read
the labels carefully and follow all safety instructions exactly.
Do not underestimate the risks to human health of handling agricultural
pesticides, regardless of whether they are synthetic or organic.
Read miticide labels carefully and follow all safety instructions exactly.
Only pesticides that have been registered or approved by the New Zealand government
can legally be used to control varroa in New Zealand. The reason for this is to ensure that
if the label directions are followed the product will be safe for beekeepers, bees, the
environment and the consumers who buy bee products.
Only pesticides that have been registered or approved can legally be
used for varroa control.
Waste pesticides should be considered hazardous to the public and to people
handling them. These materials are also potential pollutants of water, air and soil.
Used varroa control strips (e.g., Apistan, Bayvarol, Check-Mite+, Apivar) should be
taken to a local council chemical waste dump, or the supplier should be contacted for
proper disposal instructions.
Dispose of used varroa control strips properly.
It is also worthwhile marking hives with the number of strips used and the date of
application so that all strips are removed from the hive at the proper time. Strips can also
be marked with an ear-tag pen to make them easy to see in the hive.
CHEMICAL CONTROL
41
6.2 Synthetic chemicals
Synthetic chemicals usually provide the most effective and reliable varroa control.
However, they cannot be used by beekeepers producing products under organic
certification schemes, and they may not be acceptable to beekeepers who want to avoid
using chemicals in their hives. New Zealand has a long tradition of chemical-free control
of bee diseases.
The three most common synthetic chemicals used to control varroa are fluvalinate,
flumethrin and coumaphos. Less commonly used synthetic chemicals include cymiazole,
bromopropylate and amitraz.
6.2.1 Fluvalinate (Apistan)
Apistan is probably the most widely-used varroa control product world-wide. It is relatively
expensive, but is very easy to use and extremely effective. Apistan can kill nearly 100% of
mites in a honey bee colony if used according to the label directions.
Apistan consists of a plastic polymer embedded with fluvalinate, a pyrethroid. Pyrethroids
are a class of synthetic chemical that are similar in chemical structure to natural
compounds found in the flowers of Pyrethrum spp.
CONTROL OF VARROA: CHEMICAL CONTROL
Table 6.1 List of chemicals commonly used overseas for varroa control.
Product trade name Active ingredient Chemical class
Apiguard, generic thymol essential oil
Apilife VAR thymol, eucalyptol, essential oil
menthol, camphor
Apistan fluvalinate pyrethroid
Apitol cymiazole iminophenyl thiazolidine derivative
Apivar amitraz amadine
Bayvarol flumethrin pyrethroid
Folbex bromopropylate benzilate
Apicure, Mite Away, formic acid organic acid
evaporators, generic
generic lactic acid organic acid
generic oxalic acid organic acid
Check-Mite+, Perizin coumaphos organophosphate
Mark hives with the date and the number of strips used so that the strips
are removed at the proper time.
Apistan is extremely effective in killing varroa mites.
Apistan strips should be placed in the hive using one strip for every 5 frames of bees in
each brood chamber. The strip is hung between the frames, with the frames separated
slightly so that bees can contact both sides of the strip (figure 6.1). The bees rub against
the strips as they move through the brood chamber, and then pass the chemical on to
other bees as they rub up against each other in the hive.
CHEMICAL CONTROL
42
Apistan is a contact pesticide, not a fumigant, so the strips must be in contact with bees
in the brood nest at all times. The chemical is distributed best around the colony when
outside daytime temperatures are 10oC or above because the bees are less mobile at
cooler temperatures.
According to the manufacturer it is also important to suspend
the strips between the frames rather than just lay them along
the top bars. When laid on the top bars, not as much of the
chemical is exposed to passing bees, and the efficiency in
killing mites drops to 65-75%.
Apistan strips should be removed 6-8 weeks following
application because after this time their activity starts to
decline. Failure to follow this label direction can result in the
rapid development of mites that are resistant to fluvalinate.
The main problem with fluvalinate is that it is fat-soluble and
not very volatile. It can therefore be absorbed straight into
beeswax where it remains without breaking down for a long
time. As a result, Apistan should not be used during the
honey flow or while honey supers are on hives.
There are also problems with fluvalinate residues building up and persisting for long
periods of time in combs, so periodic replacement of brood combs is very important
when the product is used long-term. To avoid fluvalinate residues carrying over in new
combs, beeswax used for foundation should ideally come from fresh cappings wax.
Fluvalinate residues can also be found in propolis.
CONTROL OF VARROA: CHEMICAL CONTROL
Don’t use Apistan during the honey flow or while honey supers are on hives.
Fluvalinate residues in beeswax are an important problem in world beekeeping.
Flumethrin accumulates less in beeswax and propolis because
Bayvarol contains less active ingredient than Apistan.
Figure 6.1 An Apistan strip
being placed inside a hive.
Apistan strips only require two trips per treatment. No great increase in labour is required
since the work can usually be incorporated into standard hive management. A spring and
autumn treatment is usually sufficient to provide good varroa control. However, additional
treatments may be necessary during the acute (mite invasion) stage.
6.2.2 Flumethrin (Bayvarol)
Bayvarol strips are another commonly-used product for varroa control. Bayvarol contains
flumethrin, which like fluvalinate is a pyrethroid. Bayvarol is similar to Apistan in that the
flumethrin is embedded in a polymer strip. Like Apistan, it is also relatively expensive,
but is easy to use and only requires two trips to the hive.
Bayvarol’s method of use is identical to Apistan (although twice as many strips are
required) and it is equally effective in killing varroa. Studies suggest that the flumethrin
in Bayvarol tends to accumulate less in beeswax and propolis, since the amount of active
ingredient in the product is substantially less than in Apistan.
CHEMICAL CONTROL
43
6.2.3 Coumaphos (Check-Mite+, Perizin)
Coumaphos comes in two formulations for mite control. Perizin is a solution of
coumaphos that is trickled over bees. It is best used in the late autumn or winter, ideally
in broodless conditions. Two treatments one week apart are recommended. Perizin is used
primarily in Europe.
Check-Mite+ is a coumaphos product that is formulated into strips, so it can be used like
Apistan and Bayvarol. The strips are also very effective against varroa, are easy to use,
and the label instructions are almost identical to Apistan. Check-Mite+ has received
preliminary registration in some US states.
Coumaphos is an organophosphate. It acts as both a contact chemical (like fluvalinate
and flumethrin) and as a systemic (i.e., it works through the bee’s body). Coumaphos is
also fat-soluble and can migrate from the wax into stored honey. In Europe, coumaphos is
the varroa control chemical most frequently found in honey.
CONTROL OF VARROA: CHEMICAL CONTROL
Coumaphos can show up as residues in honey and beeswax.
6.2.4 Cymiazole (Apitol)
Cymiazole is a systemic miticide. It works through the bees’ haemolymph. Cymiazole is
not a fat-soluble substance, unlike the other synthetic chemicals mentioned. It therefore
tends to dilute easily into honey.
Apitol is a granular product that is mixed with syrup, and either fed as normal or applied
directly to the bees using a controlled dosage syringe. Two applications are made 7 days
apart for effective varroa control. Best results are obtained in the autumn when there is
little or no brood in the hive. Apitol should definitely not be used during the honey flow.
6.2.5 Bromopropylate (Folbex)
Bromoprophylate is one of the oldest varroa control substances, but is no longer used
extensively in Europe because of concerns about residues in honey. It is a fat-soluble
chemical like fluvalinate and flumethrin, and residues were still found in a significant
percentage of German honey samples 8 years after its use was voluntarily discontinued in
that country. The honey residues come from beeswax containing the active ingredient,
either in colony combs or in foundation.
Folbex contains bromoprophylate in paper strips. The strips are lit and the resulting
smoke distributes particles of the chemical around the beehive. Folbex has been shown to
kill both varroa and tracheal mites. For varroa control, four applications of one strip at 4-
day intervals is recommended. The product should not be used during the honey flow,
while surplus honey is on the hives, or when the bees are in winter cluster.
6.2.6 Amitraz (Apivar)
Amitraz is a contact miticide, but while it is fat-soluble, it is volatile and unstable in
honey. It completely degrades in 3-4 weeks, so it is not found as a residue in honey or
beeswax. Beeswax actually has an accelerating effect on the degradation of amitraz.
Amitraz is used in some countries in Europe.
CHEMICAL CONTROL
44
Apivar is a plastic strip with amitraz impregnated into it. The strips are placed into the
hive in the same way as Apistan, and for the same amount of time. Apivar is highly
effective in killing mites, and has the advantage of being able to be used during the
honey flow.
6.3 Organic chemicals
The need to develop mite control substances as alternatives to synthetic chemicals stems
from both a desire to use more ‘natural’ compounds, and concerns about residues of
synthetic chemicals appearing in bee products. Good mite controls must also be found in
addition to ones currently in widespread use because varroa mites have already shown an
ability to quickly develop resistance to a range of chemicals.
Two types of organic mite control substances (essential oils and organic acids) have been
investigated, and promising ones from both groups are now in common use, particularly
in Europe.
Several other substances (including icing sugar and vegetable oil) show some promise,
but more research is needed to prove their ability to kill high percentages of mites under
field conditions.
6.3.1 Essential oils
These are plant-derived extracts that are highly volatile (they evaporate quickly), and
have strong, characteristic odours. They are found in almost all plants, but only those
containing more than 0.1% oil are classified as ‘essential’ oils.
Essential oils perform various functions in plants. They are both toxic to pests and repel
them. They also protect plants from bacteria and fungi. Essential oils are now often
used in natural pesticide products such as citronella candles and linalool anti-flea
pet shampoos.
CONTROL OF VARROA: CHEMICAL CONTROL
Essential oils are compounds plants use to protect themselves from pests.
Over 150 essential oil compounds have been tested for their ability to kill varroa mites.
Those with high evaporation rates were best at killing mites. However, to be effective, the
oils must also not readily kill bees, and under test conditions only nine of 24 highevaporation
essential oils killed less than 10% of bees. A problem with essential oils
compared with a chemical such as fluvalinate is the small difference between the amount
of the substance that will kill mites and the amount that will kill bees. Fluvalinate is 800-
1000 times more toxic to varroa than to bees, whereas the best essential oils are only two
to four times more toxic.
While a number of essential oils kill varroa, many of them are also
toxic to bees.
Essential oils are generally not considered toxic to humans, although wintergreen is a wellknown
exception, and thymol can be hazardous if it gets into the eyes. Essential oils can
be absorbed into beeswax and then dissipate over time. They can also create taste and
odour taints that can be detected by consumers. The Swiss have therefore used human
taste panels to develop minimum residue limits for some mite control essential oils.
Essential oils used to control varroa can cause noticeable taints in honey.
CHEMICAL CONTROL
45
Rather than review all of the research that has been carried out on essential oils and
varroa, what follows are descriptions of several substances that have shown good results
and are in common use as mite control substances. Other products (e.g., wintergreen oil,
neem oil, manuka oil) show some promise, but more work is needed on hive application
methods before they can be recommended as suitable organic control substances.
6.3.1.1 Thymol
Thymol is an essential oil extracted from the thyme plant. The amount of thymol in the
thyme plant depends on the variety of plant. The type of extraction method also has an
influence on the chemical composition. Lack of consistency in composition affects the
ability of the compound to kill varroa mites.
Thymol is the only essential oil that is widely used, kills high percentages of mites, and
does not kill significant numbers of bees. Tests have shown thymol kills 66-98% of mites,
and has been shown to be as effective as formic acid in a number of tests. Thymol’s
effectiveness is similar for various application methods, including powder suspended
between frames in mesh bags, liquid poured on a sponge on the top bars, and a
continuous evaporator placed between the brood combs.
CONTROL OF VARROA: CHEMICAL CONTROL
Thymol is effective in killing mites and is not toxic to bees.
Thymol kills a greater percentage of mites when there is little or no brood, since the
vapours do not penetrate the brood. Air temperatures also need to be generally above
12oC and preferably above 15oC. Timing of treatments is therefore very important.
Instructions for thymol application are included in appendix 4.
For thymol to be effective in killing varroa, timing of application and outside
air temperature are very important.
Thymol leaves taste residues in honey and wax, but the residues do not persist for long
periods of time. Studies have shown that if the product is applied after the honey flow,
levels approaching the taste threshold (1.1 ppm) will not be reached in honey produced
the next season.
6.3.1.2 Apiguard
Apiguard is a formulation of thymol in a gel. The gel is designed to be easy to apply and
gives a more controlled release of vapours than other methods. Bees also pick up the gel
on their body and move it around the hive, which results in better dispersal. Two
formulations are available overseas - a single pack for hobbyist beekeepers and a bulk
container with enough for 30 colonies. The dose rate is designed not to harm either bees
or brood, although some killing of young larvae has been noted in Canadian trials.
Gel varroa control products have a more controlled release of vapours and
are also moved around on the bodies of the bees.
The Canadian trials on Apiguard also showed lower rates (68-82% mite kill) than Spanish
studies (98%). However, the Canadian work was conducted during the middle of summer
with large amounts of brood in the colony, and the label recommends that the product is
used in late summer after honey has been removed. There needs to be low levels of brood,
but high enough temperatures, for the product to work effectively.
CHEMICAL CONTROL
46
6.3.1.3 Apilife VAR
Apilife VAR is a combination of thymol (76%), eucalyptol, camphor and menthol, with
20 g impregnated in a vermiculite tablet. A tablet is placed on the top bars at the end of
summer after the honey is taken off, and replaced with a fresh one 3-4 weeks later.
Temperature and lack of brood greatly affect Apilife’s ability to kill mites. Daytime
temperatures shouldn’t fall below 12oC for long periods.
Under optimum conditions, mite kill can be 97% for one-super colonies, and 90-95% in
two-super colonies. Studies indicate that thymol is the ingredient producing most of the
effect, and the other essential oils are not important.
CONTROL OF VARROA: CHEMICAL CONTROL
Daytime temperature is very important for Apilife VAR to work effectively.
Because the product can give inconsistent results at low temperatures, it is recommended
that a treatment with oxalic or lactic acid follows if natural mite drop two weeks after the
end of treatment is greater than one mite per day.
Apilife VAR used in conjunction with mesh bottom boards has been shown to kill a higher
percentage of mites than Apilife VAR on its own.
6.3.2 Organic acids
Organic acids are also compounds found in nature, and some have uses as pesticides.
One organic acid, formic acid, was originally shown to be effective in treating honey bees
infested with tracheal mites. It has now also been shown to kill varroa. Two further acids,
lactic and oxalic, have been commonly used as varroacides in Europe for years.
All three acids are found naturally in trace quantities in honey. However, when applied for
mite control they can each leave noticeable tastes in honey, so the Swiss have also
developed maximum residue limits for these products. Honeys with high aroma can
tolerate higher levels of organic acids without becoming noticeably tainted than can low
aroma honeys.
The organic acids used in varroa control are also found naturally in trace
amounts in honey.
6.3.2.1 Formic acid
Formic acid has proved to be a useful tool for varroa control in a number of countries. It
does, however, have two disadvantages. The first is that it can have a high labour cost
since some methods of application require multiple visits (up to 6 per apiary). The other
disadvantage is that it can be hazardous to use.
Formic acid is a hazardous chemical to use and special care needs to be
taken to ensure that it is handled safely.
Formic acid is widely used in Canada and Europe. A gel form is also the first organic
varroa control substance approved in the United States. Original studies showed that a
65% solution could kill 94% of mites if applied on one or two absorbent pads for 4 days
and then repeated three times. However, the number of visits required made use of the
substance uneconomic for commercial beekeepers, so various absorbent and slow-release
devices were developed to hold more of the product and disperse it over a greater length
of time.
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A variety of absorbent materials in plastic bags, including newspaper, towelling,
potholders and pressed paper board are used in Canada. Most beekeepers produce these
themselves. However, a relatively new commercial bagged product called Mite Away is
becoming very popular.
The bag, containing 250 ml of 65% solution and the absorbent material, has windows cut
in it before being placed on the top bars of a hive. The number of windows depends on
the size of the hive. The bag and absorbent provide effective control with one application,
although 20 days later another 50 ml of formic acid can be added if mite fall is still
significant. The bags are used in either mid-spring, or late summer after honey has been
removed. Outside temperatures need to be at least 10oC, but not greater than 30oC (since
above this temperature formic acid can cause slight bee toxicity and queen loss). Further
instructions are given in appendix 2.
An application device originally developed in Europe involves putting 250 ml of 65%
solution on a 20 x 24 x 1.5 cm piece of soft fibre building board (e.g., Pinex), then
sealing it in a freezer bag. Holes 1.5 cm across are punched in the plastic with a round
tool. The number of holes depends on the hive type and the temperature. Late summer or
autumn treatment is normal, with outside temperature at least 10oC.
The effectiveness of the treatment can be judged by weighing the board and bag. If
evaporation is 7 g or more per day, 95% of mites can be expected to die during a 14-day
treatment period. Effectiveness goes up to 97% at 10 g per day, but decreases
significantly below 7 g per day. Boards can be reused by adding more formic acid.
In Europe, a variety of plastic devices have also been developed over the past 20 years to
provide controlled slow release and diffusion of formic acid. Some of these devices have
adjustable openings to regulate evaporation of the compound.
A gel product called Apicure has also been developed that distributes a given amount of
formic acid (30 g of 65%) over time. Concentrations of formic acid in beehives from a
single application of the gel were found to be the same or greater than four successive
applications of the liquid form. In tests on colonies in the spring, the product killed 70%
of mites. Apicure has been registered in the US, but since it has not been shown to have
a consistently high degree of varroa control, the label states that it is useful for the
‘suppression’ of varroa.
An important advantage of the gel product is its relative safety for beekeepers. Formic
acid will burn skin and eyes if the beekeeper is exposed to either the chemical or its
vapours. It is also harmful or fatal if swallowed. Formic acid vapour is heavier than air,
and concentrations of 18-57% are combustible if they come into contact with an open
flame or spark. The gel product is safer to handle than liquid formic acid because it has a
slower release of vapour.
CONTROL OF VARROA: CHEMICAL CONTROL
Formic acid will burn skin and eyes, is fatal if swallowed, and fumes of the
chemical can ignite. Always wear acid-proof gloves and eye protection when
handling liquid formic acid.
It is often suggested that formic acid is able to kill varroa in capped brood cells as well as
mites on adult bees. Tests where brood combs were fumigated in closed plastic foam
boxes at 50 ml for 1 hour killed 100% of mites in the brood cells with 90% of the brood
surviving the treatment. However, there is dispute as to whether formic acid kills mites in
CHEMICAL CONTROL
48
brood under hive conditions, since not enough of the acid vapour may circulate around
the combs and penetrate the brood.
Formic acid also appears to cause drone eggs to be removed from combs and can
therefore affect drone production. Application of the compound reduces the survival of
adult drones, with about half as many making it to 10 days old (sexual maturity)
compared with drones in untreated colonies. Formic acid should not be applied to
colonies that are being used for drone rearing (queen mating) purposes.
CONTROL OF VARROA: CHEMICAL CONTROL
Formic acid should not be applied to colonies being used for drone rearing.
Residues of formic acid can be found in honey and beeswax, although trace amounts of
the compound also appear naturally in honey. The threshold for taste residue in honey is
150-600 ppm, depending on the lightness in flavour of the honey. If formic acid is
applied in the autumn, residues in honey stores the next spring are likely to be 40-200
ppm, while residues in new honey are likely to be 25-50 ppm, depending on the type of
honey. In Denmark, honey from colonies not treated with formic acid was found to have
about 20 ppm, while a sample of retail honey had about 38 ppm. Residues of formic acid
do not build-up over time in beeswax in the way chemicals such as fluvalinate do.
Varroa has not yet shown resistance to formic acid, and researchers are not sure how the
compound actually kills mites. What is known is that while formic acid is effective (70-
80%), it is not as effective as synthetic chemicals such as fluvalinate. Success depends
on the amount used, the strength of the colony, and the ambient temperature. Best mite
kill rates are obtained when outside temperatures are high enough to achieve good
evaporation. Beekeeping practice overseas suggests that for effective control of varroa at
levels below an economic threshold, the product should be used either in conjunction with
other synthetic or organic chemicals or with biotechnical methods such as drone trapping.
For effective varroa control, formic acid should be used with other
chemicals and/or biotechnical controls.
6.3.2.2 Oxalic acid
Oxalic acid is a more recent addition to the arsenal of organic acids used for varroa
control. Oxalic acid is a corrosive, poisonous acid like formic acid, and is used in textile
finishing and as a cleanser.
Swiss research showed that 3% oxalic acid, sprayed at 3-4 ml per comb side in broodless
colonies, killed 98% of mites. In colonies with brood, however, the efficiency was 30-
40%. The researchers recommend one treatment at the end of summer if natural mite fall
is more than one mite per day during mid-summer. If there are more than five mites
falling per day at the beginning of autumn, a second treatment is required. This should
generally be sufficient to achieve good mite control, although there may be a significant
die-off of over-wintering bees.
A new application method for oxalic acid has recently been developed in Europe. The
method involves mixing oxalic acid crystals into 1:1 sugar syrup, and then pouring a
measured amount between the combs in early winter, directly on the bees. The colony
should be broodless, and the syrup should be lukewarm to avoid chilling bees. Outside
temperature should be above 0oC. The oxalic acid does not work through evaporation, so
temperature is not as important as it is with essential oils or formic acid.
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Research suggests that while there is little difference in effectiveness between 4.2%
oxalic acid in the syrup and 3.2%, the lower concentration doesn’t affect colony buildup
as much the next spring. Higher concentrations can affect over-wintering and spring
development in cold climates. Five millilitres of the syrup is applied per frame covered
in bees, using a graduated syringe. Instructions for oxalic acid application are included
in appendix 3.
The big advantage of the trickle system is the decrease in labour costs, since the frames
don’t have to be taken out of the hive. The material can also be used to treat newly
made-up nucs or splits during the broodless period that occurs prior to a new queen
beginning to lay.
As with formic acid, extreme care must be taken when handling oxalic acid because it is
corrosive. A dust mask, goggles and chemical resistant gloves must be worn when
handling the pure chemical, and the syrup should be mixed only in a well-ventilated
room or outside.
CONTROL OF VARROA: CHEMICAL CONTROL
A mixture of oxalic acid and sugar syrup trickled between combs in winter
is a low-cost form of organic acid varroa control.
Extreme care must be taken when handling oxalic acid because it is corrosive.
Oxalic acid can also produce noticeable tastes in honey, and the Swiss maximum residue
limit for taste is 400-900 ppm. However, when applied in autumn no noticeable increase
in oxalic acid residue was found in honey produced the following season.
6.3.2.3 Lactic acid
Lactic acid is a compound found naturally in milk, molasses, and various fruits and
wines. It is also found in small quantities in honey. Lactic acid is used in a wide range of
products, including adhesives, plastics and pharmaceuticals.
In the 1980s, researchers in Germany showed that lactic acid was effective in killing
varroa, and field trials using a backpack sprayer with a dosage (drench) gun confirmed
that 8 ml of 15% lactic acid applied to each comb face killed 92-99% of mites with very
low bee mortality. However, up to 60% of bee eggs were sometimes removed immediately
after treatment. The other major drawback identified was the time required, at about 12
colonies per hour.
Since that time lactic acid has become an important component of biological mite control
programmes in Europe. Normal mite kill for the product in broodless hives is considered
to be about 80%. However, if the material is applied to colonies with brood, the
effectiveness drops to 20-40%. As a result lactic acid is normally used as a mite control
in late autumn. Hand sprayers are generally used because they can be worked with one
hand while the other holds the frame. To apply the required 5-6 ml of 15% lactic acid,
four to six pumping strokes are required. Overdosing is said to be a problem, particularly
in late autumn, so care is needed in applying the material. Chilling can also occur,
although in Germany the material is applied even when the outside temperature is 0oC.
Lactic acid can be effective in killing varroa if it is applied to
broodless colonies.
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Applicator safety is not as important with lactic acid as it is with formic acid. However, it
is still recommended that protective goggles and chemical resistant gloves are worn when
handling the bulk product.
Of the three organic acids used for varroa control, lactic acid produces the least
noticeable residues in honey. Swiss researchers have determined a maximum residue limit
affecting taste at 800-1600 ppm. When lactic acid is applied in the autumn, the levels in
stored honey go up to 1500 ppm, but 4 weeks later they are below 500 ppm, less than
the maximum residue limit. Lactic acid can also be used in the spring without causing
significant residues, provided it is applied more than 8 weeks before the nectar flow.
6.3.3 Vegetable and other oils
Vegetable oils have been shown to be effective in the control of tracheal mites. The oil is
administered as vegetable shortening mixed in a sugar patty. The oil doesn’t kill the mite
directly, but instead makes the bees unattractive or unrecognisable to the mite.
Vegetable oils have been used to control varroa as well, and several commercial
formulations have been developed that are claimed to kill good percentages of mites.
However, research is somewhat contradictory about their effects.
Danish researchers trialed a formulation (canola/rapeseed oil with an emulsifier), as well
as soybean oil with different emulsifiers. The oils were either sprayed on bees or
administered in patties. While the oils with high concentration of emulsifier killed high
levels of mites (up to 97%), the side effect was significant bee deaths (over 50%). Oil
mixtures with less emulsifier were not effective in killing mites. Oil patties similar to
those used with tracheal mites did not significantly reduce varroa levels. The researchers’
conclusion is that vegetable oils do not seem a realistic alternative to organic chemicals
for varroa control.
CONTROL OF VARROA: CHEMICAL CONTROL
Studies suggest that vegetable oil, while killing varroa mites, is also
toxic to bees.
French researchers have trialed both canola/rapeseed oil and mineral (paraffin) oil with an
emulsifier (Tween at 5%). Hives were sprayed with 6-10 ml of the oil frame by frame in
autumn when colonies contained only small amounts of brood. The oil was applied once
per week for three weeks. The best effect was for the mineral oil and Tween mixture, with
97% mite kill after two applications and 99.5% after three. There was some bee mortality
with the mixture, but mostly due to the manipulation of the frames. The substance didn’t
affect the brood.
The French researchers concluded that the mineral oil/Tween mixture stayed longer and
was better spread on the bodies of the bees than the canola/rapeseed oil mixture. This
indicates the oil might affect the ability of the mites to remain on the bees. Time required
for application seems to be the major drawback, at 5-10 minutes per colony. The product
is recommended for use with mesh bottom boards to keep fallen mites from re-entering
the hive.
6.3.4 Icing sugar
Since icing sugar has proved to be an effective means of surveying bees for varroa mites,
research has recently been conducted in Finland to gauge its effectiveness as a miticide
in colonies. Fifteen grams of the sugar was dusted between the combs of two-storey
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51
colonies in mid-summer, with different combinations of days and times between
treatments. Mite fall was then measured with paper boards below mesh screens.
The average mite fall on the treated colonies was between 47 and 56 times greater than
the control colonies. A treatment once every 3 days showed the best results in reducing
mites, although total efficiency of the method was not calculated.
Work still needs to be done to determine the best methods, but it appears that super-fine
icing sugar together with mesh bottom boards may offer a bee-friendly (and even bee
stimulating) mite control alternative that can be used at all times of the year without fear
of residues. Because the sugar interferes with the mite’s ability to cling to the bees, the
researcher suggests that mite resistance will not develop.
CONTROL OF VARROA: CHEMICAL CONTROL
More fieldwork is needed to prove the efficacy of icing sugar as a
varroa control substance.
6.3.5 Outlook for organic chemical controls
Because there are significant residue and resistance problems with synthetic varroa
control chemicals, beekeeping industries and researchers around the world are working
hard to develop effective organic chemical alternatives.
However, these points should be borne in mind when considering organic chemicals as
alternative varroa controls:
• Some organic chemicals can kill significant numbers of bees and can be extremely
hazardous to beekeepers.
• No organic chemical is currently as effective as synthetic chemicals.
• Any organic chemical at this point needs to be used in conjunction with
biotechnical methods or other organic or synthetic chemicals to keep mite levels
below colony damage thresholds.
• Application systems for organic chemicals need to be improved to regulate the
dose, allow for prolonged application without having to return to the hive, and
ensure proper dosage is maintained even when temperature conditions fluctuate.
• Mites can also develop resistance to organic control substances such as essential
oils and organic acids.
6.4 Avoiding chemical residues
Residues resulting from the use of chemicals in agriculture are a major problem in food.
Beekeepers in New Zealand have already faced residue problems in the past. For
example, lead and zinc residues were once a problem for some beekeepers because of
galvanised drums, solder on extraction equipment, and lead paint on honey supers.
The idea of having pesticide residues in honey and beeswax runs counter to the
philosophy of most beekeepers in New Zealand. However, with the advent of varroa it is
certain that miticide residues will be found in bee products produced here. The very high
sensitivity of testing procedures means that residues can be detected in many bee
products. Modern laboratory analysis can routinely detect chemical compounds in the
order of 1 part per billion, or the equivalent of 1 teaspoon of a pesticide mixed into
25,000 drums (nearly 7,700 tonnes) of honey. Some chemicals such as fluvalinate
persist in beeswax, so concentrations will increase within the beehive each time a
treatment is applied.
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The presence of chemical residues in honey has the potential to devalue bee products
and create consumer resistance. Honey buyers and importers are also likely to require
product to be tested for residues as part of their terms of trade.
Residues can be minimised in five important ways:
• Choose pesticides that because of their chemical structure are least likely to
contaminate the product that is being harvested. Varroa treatments vary in their
tendancy to leave residues in bee products. Consider this factor when designing a
treatment programme.
• Time the use of the miticide so that it will not come into contact with the product being
harvested. Care also needs to be taken with the honey frames that may be in the
brood nest. In some beekeeping operations, and especially during manuka honey
production, frames from the brood boxes are often extracted. This practice is likely
to result in increased residues in honey for fat-soluble mite control chemicals such
as fluvalinate and flumethrin.
• Reduce the total amount of pesticide used by only applying products when mite
populations reach economic threshold levels. However, this should only be done
once the acute phase is over and invasion of mites from feral and untreated
colonies is not a major problem.
• Carefully follow the label instructions on the products. These instructions have been
designed to minimise residues. A good example is removing miticide strips at the
end of the treatment, rather than leaving them inside the hive.
• Only use registered products. For instance, don’t use Mavrik instead of Apistan,
even though it may appear cheaper. Mavrik has a much higher dose of fluvalinate
than Apistan, and home-made products cannot achieve the careful release given
by Apistan. Based on overseas experience, Mavrik’s use in beehives would result in
significant residues in honey and the development of quicker resistance to
fluvalinate by mites (see chapter 7).
CONTROL OF VARROA: CHEMICAL CONTROL
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7. CHEMICAL RESISTANCE
This chapter explains what chemical resistance means in relation to varroa, and
outlines what can be done to reduce the chances of varroa developing resistance
to chemical controls.
7.1 What is chemical resistance?
Chemical resistance occurs when a pest such as varroa becomes more and more able
to withstand a pesticide that is being used, so that the chemical no longer kills most of
the pest population.
The word ‘resistance’ is also sometimes used in association with varroa to describe the
ability of honey bee colonies to live with an infestation of varroa. However, the word
‘tolerance’ has been used throughout this book to describe that ability, in order not to
confuse the two terms.
7.2 Why resistance happens
The process of sexual reproduction results in genetic variation. Offspring do not look
exactly like their parents because only half of each parent’s genes are represented in
any egg or sperm, and because there is chance involved in which one of those sperm
combines with an egg in the fertilisation process. Random mutations of chromosomes
can also add further variation.
Eye, hair and skin colour are a few of the many variations found in the human
population. While for us such differences may seem inconsequential, the variation in
the characteristics of individual animals or plants in a population is highly important in
an evolutionary sense. It means that when conditions change, there will usually be
some members of the species that are physically able to survive. If not, the species
becomes extinct.
The individuals that are better adapted are more likely to reproduce and pass on their
genes to the next generation. These genes then become more and more common in the
population, while genes that are not well adapted become less and less common.
It is this process that allows varroa to become resistant to pesticides. Under ‘normal’
circumstances, the resistant mites are not usually as good at surviving as the nonresistant
mites (hence the reason their genes are not well represented in the mite
population). However, when mites come into contact with the chemical, most of the
susceptible mites die while most of the resistant mites survive. Over time, as more
generations of mites are produced, the genes of the resistant mites become
widespread in the population, while the genes of the susceptible mites are found less
and less.
Interestingly, if the pesticide is no longer used, the percentage of resistant mites in the
population will usually decline. The reason is that there is generally some other
significant survival advantage inherent in the susceptible mites that allows them to be
more successful in breeding more mites at times when the chemical is not in use.
An example of how the populations of resistant mites change with repeated miticide
use is presented in figure 7.1. The red dots are the resistant mites.
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54
7.3 Creating resistant varroa in the laboratory
The pesticides used for varroa control have been selected because they kill most or all
varroa when the recommended dosage and usage pattern is followed. Before government
authorities allow a pesticide to be sold, scientific studies must be carried out to show that
the chemical is highly effective in killing mites.
However, by exposing varroa to very low concentrations of the pesticide, scientists have
shown that it is possible to select for mites that show some resistance to the chemical.
The varroa might have a slightly thicker cuticle that protects them from the pesticide for
slightly longer, or they might have enzymes that can break down some of the pesticide
before it causes damage.
Scientists have shown that by keeping the varroa in constant contact with low
concentrations of the pesticide, only mites with the resistance are likely to breed. Slowly
increasing the concentration of the pesticide will result in the selection of more and more
resistant mites until mites are selected that are resistant to the full strength of the
pesticide.
7.4 How beekeepers have created resistant varroa
Beekeepers have unwittingly created resistant varroa in a very similar manner to the way
scientists do it in the laboratory.
7.4.1 Use of Mavrik
Apistan strips contain the pesticide fluvalinate. The strips are formulated to slowly release
fluvalinate at a constant rate for a given period of time to control varroa. The strips should
be removed after this time. The strips are expensive, however, and it didn’t take
beekeepers overseas very long to discover that Mavrik, a common horticultural spray, also
CONTROL OF VARROA: CHEMICAL RESISTANCE
Initial varroa population
Miticide treatment
Two months later
Miticide treatment
Miticide treatment
Two months later
Two months later
= Not resistant = Resistant
Figure 7.1 Development of chemical resistance
CHEMICAL RESISTANCE
55
contains fluvalinate and is a fraction of the cost of Apistan strips (Mavrik is a bulk liquid
rather than an expensive, slow-release plastic strip). Beekeepers found that pieces of
cardboard dipped in a very weak Mavrik solution were very effective at controlling varroa
in beehives.
However, because Mavrik dissipates quickly (i.e., it is not in a slow-release strip), using
Mavrik on cardboard resulted in varroa being exposed to lower concentrations of
fluvalinate than with Apistan. Beekeepers found that they had to use increasingly more
concentrated Mavrik solutions until not even 100% Mavrik was giving good control. Worse
still, because Apistan also contains fluvalinate, Apistan was now also ineffective against
the resistant mites. Use of Mavrik to control varroa has also been implicated in findings of
fluvalinate residues in honey.
CONTROL OF VARROA: CHEMICAL RESISTANCE
Don’t put beekeeping at risk by using non-approved chemicals like
Mavrik to control varroa.
7.4.2 Incorrect use of miticide strips
Apistan strips are designed to be left in hives for only 6-8 weeks, during which time they
release a constant amount of fluvalinate per day. After that time, the amount of
fluvalinate released begins to decline. For this reason, the strips must be removed.
Otherwise, the mites will be exposed to low concentrations of fluvalinate and will build
up resistance.
Some beekeepers overseas have shown that while they are good at putting the strips in
the hives, they can sometimes be tardy in removing them. When they put the strips in
hives in spring, they just add them to the strips that were placed in the hives the
previous autumn and spring. This practice has probably produced resistant varroa by
exposing mites to low concentrations of fluvalinate.
Another practice that can produce resistant mites is to cut Apistan strips in half. The
practice may appear to save money, but in the long run it can cost beekeepers dearly.
7.5 Cross-resistance
Cross-resistance is where a varroa mite that becomes resistant to one chemical
automatically becomes resistant to another that is either chemically very similar or acts
on the mite in a similar way. An example of cross-resistance is where mites that have
become resistant to fluvalinate (Apistan) are also found to be resistant to flumethrin
(Bayvarol), a pesticide very similar in chemical structure to fluvalinate. Interestingly,
some of these mites have also shown resistance to amitraz (Apivar), even though it is
from a different chemical class.
7.6 Slowing resistance
Varroa is likely to build up resistance to all pesticides (both synthetic and organic), given
enough time and misuse of products. Varroa resistance has so far been reported to
acrinathrin, armitraz (Apivar), bromopropylate (Folbex), chlordimeform, coumaphos
(Check-Mite+, Perizin), flumethrin (Bayvarol) and fluvalinate (Apistan).
There are, however, a number of things that can be done to slow the resistance process:
• Only use registered products.
• Follow the instructions on the label.
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56
• Only use the pesticide when it is needed.
• Use the recommended concentration of pesticide so that mites are not exposed to
low concentrations.
• Remove the pesticide when recommended, again so varroa are not exposed to low
concentrations of the chemical. A useful tip is to mark the hive with the date of
application and the number of strips so it is obvious when the strips need to be
taken back out.
• Do not re-use strips.
• Don’t rely on just one chemical. Alternate chemicals that are from different
chemical classes to reduce the chance of cross-resistance. An example of this
approach is the use of fluvalinate in the spring and formic acid in the autumn,
rather than Apistan and Bayvarol (which are from the same chemical class). The
formic acid treatment will kill most of the fluvalinate-resistant mites and the next
fluvalinate treatment will kill most varroa that have become resistant to formic
acid. Eventually, mites might develop resistance to both formic acid and
fluvalinate. However, this will hopefully take a long time.
• Encourage other beekeepers to also use techniques that will delay resistance. Any
resistant mites they produce will eventually find their way into other beekeepers’
hives.
To delay resistance:
• Only use registered products.
• Follow the instructions carefully.
• Alternate control methods.
7.7 How to measure resistance
When resistance occurs, it usually does so slowly and in isolated localities, after which
time the resistant mites spread further afield. Early detection of mite resistance is
therefore important to avoid major losses of beehives that have been unknowingly treated
with an ineffective chemical.
The first sign of resistance is usually a colony or colonies that have high levels of varroa
still present after a treatment has been applied. However, because high mite levels can
also be caused by invasions of varroa from other colonies, it is important to test suspect
mites for resistance. The US Department of Agriculture has developed a test for
resistance to Apistan. Directions on how to carry out the test are included in appendix 5.
CONTROL OF VARROA: CHEMICAL RESISTANCE
If your chemical control method does not appear to be working, make
sure to test the varroa for chemical resistance.
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8. BIOTECHNICAL CONTROL
This chapter describes various non-chemical methods that can be used to
control varroa.
8.1 What does ‘biotechnical’ mean?
‘Biotechnical’ is a word that is now often used to describe non-chemical mite control
methods. There are a number of beekeeping management practices that are likely to affect
mite populations, but biotechnical control can probably best be defined as beekeeping
management techniques specifically designed to reduce mite levels in a colony.
‘Biotechnical’ means beekeeping management techniques specifically
designed to reduce mite levels in a colony.
Biotechnical varroa control methods have been developed for a number of reasons,
including:
• requirements of organic (non-chemical) production;
• fear of chemical residues and chemical resistance; and
• high cost or inability to obtain chemical control substances.
Biotechnical methods are generally not used as a complete means of varroa control.
However, they are often incorporated into integrated pest management systems, whether
with synthetic chemicals, or more generally with organic control substances.
8.2 Brood removal and trapping
Brood removal for control of varroa is based on the understanding that mites are confined
in brood cells once the cells are capped. The mites can therefore easily be removed from
the colony without the mites being able to escape back onto the adult bees.
8.2.1 Worker brood removal
Removing all sealed brood over a 24-day period has been shown to have a 90% efficiency
in removing varroa from honey bee colonies. Systems have also been developed to isolate
the queen on single combs, and then shift the queen to another frame at intervals, so that
the brood acts as a trap for mites seeking a place to reproduce. Three brood combs
produced in nine-day intervals and then removed in a further nine days will trap about
79% of mites in a normal sized colony. The brood combs themselves are sometimes
subjected to formic acid or heat treatment outside of the colony.
The main problem with worker brood removal is that it requires a large number of frames
to be removed to achieve good control, and the removal of frames will obviously affect the
population and productivity of the colony.
Removal of worker brood can reduce mite levels, but it also greatly
affects colony productivity and is labour intensive.
8.2.2 Drone brood trapping
Probably the most well-known biotechnical control method for varroa is drone brood
removal and trapping. Drone brood is generally used for this purpose because varroa mites
show an 8 to 10 times greater preference for drone brood than for worker brood. Far less
BIOTECHNICAL
CONTROL
58
brood needs to be removed from the colony compared to worker brood to achieve good
results, and the effects on the colony are not significant (unless drones are required for
queen mating purposes).
CONTROL OF VARROA: BIOTECHNICAL CONTROL
Drone brood trapping reduces mite populations and doesn’t affect colony
productivity.
European researchers have produced theoretical models of the effect of drone brood
removal on varroa populations. They assumed insertion of a frame with 1500 drone larvae
into the centre of the brood nest, followed by the removal of the frame and destruction of
the brood 1 week later after the brood had been capped. Their model showed that if this
was carried out twice, one month apart at the beginning of summer, the mite population
in a heavily infested colony reduced from 16,000 mites to about 1750 (89%), provided
there was no reinvasion of mites from other colonies.
The results of the theoretical model have been confirmed in field studies. Drone brood
removal can at least temporarily halt the growth of mite populations in the colony.
However, a mite population of 1750 in the middle of summer is considered by many
observers to still be high enough to require some type of further treatment in the autumn.
The problems with inserting drone brood into a large brood nest are that 1) there are a
number of mites already inside capped brood cells that cannot transfer to the inserted
drone brood, and 2) the large amount of worker brood in the colony, in addition to the
inserted drone brood, competes for mites against the drone brood, even if the drone brood
is more attractive to mites.
These problems can be overcome, however. The theoretical model showed that if one
comb of drone larvae was inserted into a broodless colony and removed a week later
(trapping), it would reduce mite populations by 92.5%. Two combs reduced the
populations even further to 99.4%, equal to the most effective chemical mite treatment.
Drone brood trapping in a broodless colony can reduce mite populations
at a similar rate to chemical controls.
As a result of this modelling, the researchers have now developed methods that
incorporate drone brood trapping of mites into beekeeping management systems for
swarm control and hive increase.
Drone comb can be made by taking a good, well-drawn comb, cutting a semi-circle out
of the bottom portion, and then putting it back into a strong colony just before the
honey flow for the bees to draw out. Another good method is to put a 3/4 depth frame in
the middle of a full-size brood super in the late spring. The bees will draw out the
remaining bottom quarter with drone cells that can easily be removed once the drone
brood is capped.
8.2.3 The hive splitting varroa control method
This method of varroa control using hive splitting was developed by Dutch researchers,
and is based on both the theoretical model of varroa population growth and techniques
for biotechnical control of varroa that originated in Vietnam (see 12.6). The method
should be used during swarm control in the late spring/early summer, or when making
‘autumn’ splits in the late summer while the honey flow is still on.
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Step 1
• Choose two colonies.
• Place a comb with empty drone cells in the centre of the brood nest of one colony
(colony A).
Step 2 (one week later)
• In colony A, shake all the bees off the combs with brood except the drone comb,
and put the brood in the other colony (B), after first checking for AFB.
• Put a second, empty drone comb in the centre of the brood nest of colony A.
• Put the queen in colony B above a queen excluder in a further super with empty
combs.
Colony A now only has a single frame of uncapped drone larvae and an empty drone brood
comb, while colony B has a two super brood nest plus a third super containing the queen.
Step 3 (one week later)
• Remove the comb that now has capped drone brood (and mites) from colony A
(the comb that contained uncapped drone larvae the week before). The comb can
be uncapped with a knife or cappings scratcher and the drone pupae can be
removed from the comb in a small hand extractor, washed out with a hand spray
nozzle attached to a garden hose, or simply shaken out on the ground. Drone
pupae make excellent chicken feed.
• Put this cleaned comb (or another clean drone comb) into the centre of the brood
nest of colony A.
• Shake all the bees off the new brood that has been produced above the excluder in
colony B. The brood is all too young to contain any mites. Move the brood to
colony A, after first checking for AFB.
• Take the bees and queen from the excluded box in colony B and make a broodless
split (colony C). Shake all the bees off the second drone comb in colony A (now
containing uncapped larvae), and put it in the centre of the super of colony C.
• Put a protected queen cell in colony B.
Step 4 (one week later)
• Shake the bees from the drone comb containing uncapped drone larvae from
colony A, and place it in the centre of the brood nest of colony B.
• Remove the comb that now has capped drone brood (and mites) from colony C and
destroy the pupae (see Step 3).
Step 5 (one week later)
• Remove the comb that now has capped drone brood (and mites) from colony B and
destroy the pupae (see Step 3).
• Check colony B for a new laying queen.
According to the field trials carried out by the Dutch researchers, on average this method
is 83.4 to 93.4% effective in removing mites from all three colonies (depending on the
amount of drone brood available for trapping). The researchers have managed 70 colonies
using this method for 5 years in Holland without using any additional, chemical control.
CONTROL OF VARROA: BIOTECHNICAL CONTROL
Drone trapping can be incorporated into normal beekeeping
management for swarm control or the making of splits.
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The researchers found that the time required to carry out colony management was not
much more than to manage the colonies they ran as controls in the experiment. The extra
time was limited to having to manage the placement and extraction of drone combs.
8.2.4 Queen isolation cages
To increase the efficiency of drone or worker brood as a mite trapping method, beekeepers
sometimes put the queen on a comb in an isolation cage. The cage is made from pieces
of queen excluder, and allows nurse bees to have access to the queen and larvae. A queen
isolation cage can easily be constructed from wood and a sheet of plastic queen excluder.
However, in the hive split method described above, the placement of drone combs into
colonies in full lay, when those colonies have had brood removed, was found to greatly
enhance the production of drone brood in those combs. As a result, a queen isolation
cage was not needed. Using a queen isolation cage is also time-consuming and can affect
colony populations because the queen is forced to only lay on the isolated comb.
CONTROL OF VARROA: BIOTECHNICAL CONTROL
Drone trapping using the hive splitting method is a highly effective way
to reduce mite populations during the production season.
Using a queen isolation cage can affect colony productivity.
8.3 Mesh bottom boards
The use of mesh bottom boards as a biotechnical control method is based on the
observation that about 20% of varroa mites (mothers and offspring) that emerge from
cells with newly hatched adult bees fall off those bees to the bottom of the colony in the
first 3 days after emergence. This natural mite fall is likely to be caused by bees grooming
themselves and each other.
Because not all of these mites are able to re-attach themselves to bees on the bottom
board, at least some mite mortality results. However, mesh bottom boards are designed to
ensure that a far greater proportion of the falling mites are not able to find a new bee to
grab on to, so the mites die of chilling and/or starvation.
Mesh bottom boards are designed to ensure a greater proportion
of mites naturally falling off bees aren’t able to re-attach
themselves and re-enter the hive.
The technique involves either:
a) modifying bottom boards by replacing all but about 100mm at the front and
50mm at the back with 3 mm opening wire mesh; or
b) making inserts using the same mesh to go on top of existing bottom boards.
One way to construct an insert (figure 8.1) is as follows:
• Using 20 mm x 20 mm timber, cut two pieces to 465 mm and two pieces to
405 mm.
• Nail and glue the 405 mm lengths to the ends of the two 465 mm lengths to
form a rectangular rim.
• Using mesh with 3mm openings, cut a rectangular piece measuring 405 mm by
505 mm.
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• Staple the piece of mesh on top of the wooden rim.
• Using 20 mm x 20 mm timber, cut one piece 365 mm in length, two pieces 505
mm in length, and two small pieces about 60 mm in length.
• Nail the 365 mm piece on top of the mesh at one end of the rim, and the two 505
mm pieces on top of the mesh at either side of the rim. Nail the two 60 mm
pieces on top of the mesh at the other end of the rim at either corner.
• The overlap created by the top pieces and the bottom pieces should hold the insert
securely together.
• The end of the insert with the two 60 mm pieces in the corners will have a gap of
about 285 mm without any top piece. This will act as the new hive entrance when
the insert is installed.
To install the insert, disassemble the hive and turn the existing bottom board around so
that the entrance faces the opposite direction. Place the insert on top of the bottom board
with the four-sided rim down, and the gap in the three-sided rim facing in the direction of
the bottom board before it was turned around. This gap will act as the new hive entrance
when the hive is reassembled on top of the insert. The opening at what is now the back of
the hive created by the old bottom board entrance serves as an easy slot for holding a
sticky board or card for counting varroa.
CONTROL OF VARROA: BIOTECHNICAL CONTROL
Figure 8.1 A mesh bottom board insert for varroa.
When the insert is put on a hive, the bottom board is
reversed from its original position and the gap in the
rim of the insert (left of picture) serves as the new
hive entrance. The old bottom board entrance (right
of picture) acts as a slot for easy insertion of the
sticky board.
A study in the US showed that while mite levels in colonies with mesh bottom boards
reduced at between 14% and 28% in the summer months, there was no significant
difference in these levels when compared to colonies that didn’t have the boards. The
study also suggested that the boards were not an effective stand-alone treatment. Since
mesh bottom boards are used by many beekeepers as part of their mite control
programmes, the effect of these boards on varroa populations needs further investigation.
The authors of the US study say that to ensure virtually no fallen mites are able to reenter
the colony, the total distance from the floor board to the top of the mesh should be
at least 50 mm (the insert described above has a total depth of 40 mm plus the depth of
the riser on the floorboard). The study also suggested that the boards were not an
effective stand-alone control.
Figure 8.2 Mesh bottom boards without a solid
floor designed for use with palletised beehives.
The hive entrance is a groove cut into the piece of
timber at the front.
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For the mesh bottom board to be effective, sticky boards are not required to trap the
mites and hold them. However, a white card (paper or plastic) is a worthwhile addition to
a mesh bottom board if the board is also going to be used to survey mite populations.
Mesh bottom boards need to be cleaned on a regular basis to avoid a build-up of wax
moth on hive debris. Wax moth feeding on debris can be eliminated by using a purposebuilt
mesh bottom board that does not have a solid floor below the mesh (figure 8.2).
CONTROL OF VARROA: BIOTECHNICAL CONTROL
Mesh bottom boards are not an effective stand-alone control method
for varroa. They are, however, very useful in monitoring mite levels.
Heat treatment, while effective in killing mites contained in brood, is
time consuming and probably not commercially viable.
8.4 Pollen traps
Pollen traps have also been studied to determine their effectiveness in reducing mite
populations. The principle involved is the same as for mesh bottom boards. Obviously the
type of pollen trap would make a significant difference to its effectiveness, since only
traps with a screen covering a wide area of the bottom of the hive would collect
significant numbers of mites. A US study showed that mite reduction using pollen traps
was insufficient to keep varroa numbers in colonies from increasing to damaging levels
without the addition of other forms of mite control.
8.5 Heat treatment
Heat treatment to control varroa is based on the observation that adult female mites are
more sensitive to temperature increases above normal brood nest temperature (34oC) than
are the bee larvae and pupae themselves.
Treating the whole hive (including the bees) has been found to be ineffective, since either
the heat will kill many of the adult bees, or the colony will regulate the temperature
downwards by fanning, resulting in the mites on both the bees and in the brood surviving.
As a result, a method has been developed to treat the brood, once the bees have been
removed, by heating it in an incubator.
The method is generally used in conjunction with queen isolation cages, or with nucleus
colonies, since all of the worker brood is treated. Studies show that if the brood is heated
to 44oC for 4 hours, 100% of the mites in the capped brood will be killed. Only about 5%
of the brood itself is killed in the process, mostly in the form of older larvae that crawl out
of the cells. Heat can also cause some deformities in adult bees that develop from old
pupae that have been treated. There is no noticeable affect on the life-span of bees
emerging from heat treated comb.
While heat treatment kills all the mites in the brood, many remain alive on the bees. So
the effectiveness of the technique in reducing mite populations depends on the size of
the colony and the amount of brood compared with the number of bees. One heat
treatment is likely to be between 50% and 80% effective in reducing the total mite
population in a hive. The method therefore is insufficient to provide total mite control
below economic thresholds. It is also quite time consuming, and is therefore probably not
worthwhile for commercial beekeepers.
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8.6 Change of cell size
Varroa prefer drone brood to worker brood, and the longer development of drone pupae
allows more varroa females to be produced in each generation. The way varroa choose
drone brood, however, is not well understood, although cell size appears to play an
important part in the process. Brazilian researchers showed that when a piece of worker
comb drawn by non-Africanised bees was put into an Africanised colony, more mites
chose the non-Africanised comb, even though both pieces of comb contained larvae
coming from the same queen. The non-Africanised comb had bigger cells than the
Africanised comb.
A US beekeeper has suggested that a change from 5.44 cm or 5.0 cm/10 cell foundation
to 4.9 cm or 4.83 cm/10 cell foundation, combined with drone comb culling, can
substantially reduce varroa populations. However, the idea still needs further study and
controlled experimentation to determine if it has an efficiency similar to other welldocumented
mite control methods.
8.7 Eliminating the production of drone brood
Because varroa reproduction rates are much higher in drone brood than worker brood, it is
argued that anything that can be done to reduce the amount of drone brood in a hive will
affect population development of the mites.
CONTROL OF VARROA: BIOTECHNICAL CONTROL
The less drone brood in a hive, the lower the varroa reproduction rate.
Beekeepers therefore often cull drone comb, although there is obviously a natural
stimulus on the part of honey bee colonies to make drone comb to ensure that drones are
available for queen mating.
It’s also important to realise that drone brood removal will not halt the population
development of the mites. Female mites will still enter worker brood cells to reproduce
regardless of whether drone brood is present or absent. The reproduction rate will just be
slower on the worker brood.
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9. BREEDING FOR VARROA TOLERANCE
This chapter provides background on how honey bees are able to tolerate varroa,
and describes attempts that are being made to breed for varroa tolerance in honey
bee stocks.
9.1 What is varroa tolerance?
Varroa tolerance (sometimes called ‘resistance’) is the ability of a honey bee colony to coexist
with an infestation of the mite. Apis cerana, the original host of varroa, has a
number of important defensive mechanisms that allow it to develop its colony population,
raise worker and drone brood, produce honey surpluses, supersede queens and swarm, all
in the presence of varroa. Varroa exists in the colony, but the populations do not grow to
damaging levels. Put simply, varroa does not kill A. cerana colonies, either as ferals or
managed hives.
Tolerance to varroa is the ability of a honey bee colony to co-exist with
an infestation of the mite.
There is also a high degree of variability of various varroa defensive mechanisms in Apis
mellifera. While these mechanisms are not nearly as highly developed as in A. cerana,
there is hope that through both natural selection and human-assisted selective breeding
at least some of the mechanisms can allow A. mellifera colonies to also co-exist on a
continuing basis with varroa infestations. The goal here is to develop A. mellifera colonies
that do not allow varroa populations to grow to levels that seriously damage colony
performance. Significant effort is being made in a number of countries to develop true
varroa tolerant strains of A. mellifera. Bee breeding is seen by many scientists as the only
viable, long-term solution to varroa control.
9.2 Varroa tolerance mechanisms
9.2.1 Apis cerana
The following varroa tolerance mechanisms have been identified in Apis cerana:
• Removing mites from infested cells (hygienic behaviour).
• Capped stage in worker brood not long enough to usually produce mated female
mites.
• Uncapping cells, removing mites and recapping cells.
• Drone pupae infested with mites becoming weakened and not removing their
cappings, thus ‘entombing’ the mites.
• Short season of drone rearing and low drone brood production.
• Grooming of worker bees by themselves and other bees, including possible
damaging of mites.
• Significant absconding and swarming, where the adult bees leave the colony and
with it the mites in the capped brood.
When the grooming and mite damaging behaviour was first discovered by researchers, this
was thought to be a major reason A. cerana was able to successfully limit varroa
populations, so efforts were made to assess the grooming and mite damaging abilities of
different strains of A. mellifera.
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However, subsequent research has suggested that the limited and seasonal production of
drones, as well as the short capped stage of worker brood, are the main reasons varroa
does not reach damaging levels in A. cerana colonies.
CONTROL OF VARROA: BREEDING FOR VARROA TOLERANCE
Apis cerana keeps varroa under control by having a short yearly drone
production period and a capped stage for worker brood that is too short
for the mites to reproduce.
9.2.2 Hygienic behaviour
Hygienic behaviour in Apis mellifera is usually defined as the ability of adult worker
bees to uncap brood and remove the contents. A. cerana also do this, but they can
actually uncap a cell, remove the varroa mites, and then recap the cell.
Hygienic behaviour in A. mellifera has been shown to have a significant effect on a
colony’s resistance to brood diseases such as American foulbrood and chalkbrood. The
behaviour has been shown to be genetically based, so strains of bee can be selected that
show a greater amount of this behaviour.
Studies have now shown that A. mellifera use the same behaviour to remove pupae
infested with varroa that they use for brood diseases, even though unlike with brood
diseases the pupae have not died. Uncapping behaviour similar to A. cerana has also
now been observed with A. mellifera. In this case, the mites have been seen to leave the
cells on their own, rather than the bees removing them. The cells are recapped later on.
Unfortunately, the rate at which A. mellifera uncaps and removes varroa infested brood
is much lower than with A. cerana, and European strains uncap four times less of these
cells than Africanised bees (8% compared to 32%). Still, many researchers believe
that hygienic behaviour is a worthwhile trait to breed for in developing varroa tolerance
in A. mellifera.
Hygienic behaviour is not as important for varroa tolerance as for the
control of brood diseases.
Honey bees can be selected for hygienic behaviour by killing brood (either with a thin pin,
or by comb freezing) and then observing whether the bees uncap and remove the brood.
Undertaking a series of tests is recommended, since the strength of the colony can also
have an effect on whether bees with a genetic predisposition for hygienic behaviour
actually carry out the task. For varroa tolerance purposes, only colonies removing more
than 95% of the brood within 48 hours should be considered hygienic.
9.2.3 Duration of capped stage
Although we tend to believe that A. mellifera worker brood is capped 8 days after the egg
is laid, and remains capped for a further 12 days, there is actually a great deal of
variability in this time depending on the strain of bees, and the difference in time is
genetically based. The Cape bee (A. m. capensis) has a capped stage that is 2 days
shorter than European strains, and differences of 1.1 days have been observed even with
Italian bees.
The length of time brood stays in the capped stage has a significant bearing on how
varroa populations develop in the hive. Male mites don’t survive outside the cell, and
since mating can only take place in the cell, a reduction in the duration of capping stage
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means that fewer mated females are produced. The fewer mated females per brood cycle,
the fewer new infested cells there will be in the next cycle. Studies have shown that even
a one-hour reduction in the length of the capped stage can produce a 0.9% reduction in
mite offspring per cycle. Calculated over a number of cycles, the result can be 8.7%
fewer mites at the end of the season.
The problem with beekeepers selecting breeder queens with shorter capping stages is that
it is very painstaking and labour-intensive.
CONTROL OF VARROA: BREEDING FOR VARROA TOLERANCE
Selection for shorter brood development time can reduce varroa
production rates, but it is difficult and time-consuming to measure.
9.2.4 Suppression of mite reproduction
Not every female mite that enters a brood cell produces offspring, and some produce only
males. The process the female goes through in the capped cell leading to mating is
complex, and still not completely understood. However, it appears that some type of
chemical ‘trigger’ obtained from the pupa is required for her to begin egg laying, and for
her offspring to mate.
The number of female mites not producing offspring (called the ‘infertility rate’) is
generally between 10 and 20% in A. mellifera colonies. There are also seasonal effects,
with infertility lower in late winter/early spring, increasing as the brood rearing increases,
and then going back down in autumn. However, mite infertility rates as high as 40% have
been found in some bee stocks, and researchers have determined that it is a genetically
based factor in the bees (suggesting lack of sufficient chemical ‘trigger’) that can be
selected for and bred.
Identifying high-infertility stocks can be time-consuming, but results from bee geneticists
in the US suggest high varroa infertility can result in slow (or even negative) mite
population growth, so it may be worth considering for dedicated queen breeders. To survey
for infertility, at least 20 mite-infested worker cells at the purple-eye pupae stage have to
be dissected. This stage is chosen because it is too late for the female mite to begin
producing viable offspring, and the young mites are easily distinguished from the dark
brown-coloured original female that entered the cell. Mite infertility is judged as either a
single dead female mite in the cell, or a single live female, but no offspring. The
percentage of infertile cells can be compared between breeder queens.
Differences in mite infertility rates offer real hope of breeding varroa
tolerant honey bee stocks.
9.2.5 Attraction of mites to brood
Bee larvae produce chemicals attractive to varroa that help the mites enter cells at the
right time (just before capping). A German researcher put sections of the same age brood
from seven different strains of bees into the same varroa-infested colony and found there
were significant differences in the number of mites entering the cells for the different
strains. This brood attractiveness also correlated with varroa population development in
hives. The obvious suggestion is that mites staying out of brood cells longer slows down
the mite reproduction rate.
Bee geneticists have found that this attractiveness is genetically based and can be
selected for in bee stocks. The problem is in determining the relative number of mites in
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cells, since different hives will have different mite numbers. A test similar to the
one performed by the German researcher can be carried out, though it would be
fairly painstaking.
9.2.6 Grooming
Grooming behaviour has been discussed above in relation to both Apis cerana and
A. mellifera. There are considerable differences between the amount of grooming
behaviour carried out in different stocks of A. mellifera. For instance, Africanised bees
groom 38% of mites, versus 5% for Italians. This was originally suggested as a reason
Africanised bee colonies in South America did not suffer significant damage from varroa
infestation. However, it has since been revealed that a more important difference is the
infertility rate, which is 50% for Africanised bee worker brood, compared with an average
of 15% for European bees.
Bee geneticists have determined that grooming behaviour is genetically based and can be
selected for in bee stocks. However, it is not considered to be an important trait to select
for when breeding for varroa tolerance.
CONTROL OF VARROA: BREEDING FOR VARROA TOLERANCE
Grooming is not considered an important trait to select for when
breeding for varroa tolerance.
9.3 Examples of breeding programmes for varroa tolerance
9.3.1 Russian stocks
Probably the best known breeding programme for varroa tolerance is the importation and
controlled release into the US of bee stock from eastern Russia. The Russian stock is
descended from Apis mellifera bees taken to that part of Russia at the end of the 1800s
with the completion of the trans-Siberian railway. A. mellifera was not native to the area,
but the original host of varroa (A. cerana) was. The Russian bees are therefore likely to be
the stock of A. mellifera with the longest exposure to varroa anywhere in the world.
Honey bees from eastern Russia are likely to be the stock of Apis
mellifera with the longest exposure to varroa anywhere in the world.
Tests carried out by the US Department of Agriculture showed the Russian stock had an
average infestation of only 7% of worker brood 15 months after having been treated with
Apistan, whereas similar US stock had 33% infestation within 12 months. A significant
difference between the two stocks was the percentage of mites found to be on brood at
any given time. For the Russian bees, this was 48%, compared to 65-75% in non-tolerant
stock. It would appear that lack of brood attractiveness slowed down the population
development of varroa in the colonies.
Breeder queens of the Russian stock were imported and kept under quarantine in
Louisiana. Queens were reared from these breeders and then tested for varroa tolerance.
The stock has now been released to commercial queen producers in the US who will make
it available to beekeepers throughout the country.
9.3.2 Arizona practical breeding programme
This programme is described in more detail in chapter 12. The programme does not use
detailed selection methods for varroa tolerance. It instead focuses on the ability of honey
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bee colonies to survive varroa infestation without treatments, and then maintains the
population of remaining colonies by isolated mating. The varroa tolerant population is
reported to have been managed since 1994 without any other mite control being used,
and with levels of varroa infestation of between 6 and 7 mites/100 bees. Queens from the
programme have been used to requeen a 600 colony enterprise, with only about 1 in 15
hives showing significant varroa damage after one season.
CONTROL OF VARROA: BREEDING FOR VARROA TOLERANCE
Varroa tolerance can be developed in honey bee stocks using simple bee
breeding techniques.
Significant differences exist in the development periods of all three
castes of honey bees.
Correlations exist between varroa infestation and a number of tolerance
factors in honey bees.
9.3.3 Selecting for shorter capped period
As discussed above, the duration of the capped period can reduce mite populations
significantly (1 hour less results in an 8.7% mite population reduction). Bee geneticists
have also shown that selecting for rapid development can result in a 5.4 hour change in
worker development in the top 10% of colonies after the first generation of selection.
Canadian researchers found significant differences in the development periods of all three
castes of honey bees (worker: 19.1-24.1 days, average 20.1 days; queen: 14.7-17.2
days, average 15.6 days; drone: 22.0-25.5 days, average 23.1 days). They used a queen
isolation cage to confine the queen to a frame for a short period of time, and then
followed the development of the eggs that were laid. They recommend that selection for
rapid development is done with worker bees because this gives a reliable estimate with
fairly small effort.
Their results have now been put into practice by a US queen producer, who selects
queens based on rapid development. Queen cells are put in an incubator on the 14th day
after the egg is laid, and then only those queens that have emerged at the very beginning
of the next day are used for breeding stock. Breeder queens are also isolated on drone
comb, with the queen only allowed to lay for a short time. The resulting drones are
emerged in an incubator. Drones emerging on the 22nd day are marked, and then allowed
to mature in an excluded queenless colony. The drones are used to inseminate selected
breeder queens.
9.3.4 Selection for low varroa infestation levels
Projects in both Canada and Germany have involved selecting colonies for low varroa
infestation levels (e.g., 24-hour mite fall), then using these as breeders for the next
generation. In both programmes, the overall varroa infestation levels have gone down in
all colonies over time. For instance, in the German breeding programme with Carniolan
stock, 164 colonies with queens from the breeding programme were compared to 232
non-programme colonies. The mite levels in the selected stock were on average 36% less
than in the non-programme stock. Correlations were found between mite infestation and a
number of tolerance factors such as hygienic behaviour, grooming, brood attractiveness
and infertility rate.
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10. INTEGRATED PEST MANAGEMENT
This chapter explains the concept of integrated pest management, and shows how it
applies to varroa control.
10.1 History of pesticide use in New Zealand
Pesticide use in New Zealand has gone through, and is continuing to go through,
a revolution. The revolution started in the 1940s, when it was thought that all our
agricultural pest problems could be solved with a ‘silver bullet’, or at least a collection
of them.
Foremost among these silver bullets was the insecticide DDT. It was inexpensive, easy to
use and very effective. We thought we had won the war against insects that were
damaging our crops, and in other countries adversely affecting human health. DDT was
used everywhere. Thousands of tonnes were applied to pasture to kill grass grub and other
pests, used in home gardens, put into water to kill mosquitoes, and even dusted on
human beings to control lice and fleas.
However, by the late 1950s, our silver bullets were starting to cause disquiet in some
quarters. Increasingly, more insects were building up resistance to DDT. Residues of the
chemical were turning up in foods such as milk and meat, and in humans, fish and other
animals. Some bird species were becoming scarce because the chemical was making
their eggshells too thin.
Rachel Carson’s book Silent spring, published in 1963, highlighted what the world would
look like if we carried on with the extensive use of pesticides. The public began to
develop an understanding of the risks of pesticides, and in the last several decades there
has been an ever-increasing pressure to reduce pesticide use, especially for chemicals
that persist in the environment, kill a wide range of insects and have adverse
environmental effects.
Domestic consumers and overseas markets are demanding reductions in
pesticide use.
All areas of agriculture in New Zealand have been affected by these pressures, but most
especially those relying on export markets. We have seen the growth of a number of
organic and low-pesticide-use movements, both here and overseas. Some of our important
markets are also not only demanding product without pesticide residues, they are
requiring proof that the food was produced in a sustainable way that didn’t cause
ecological damage to the countryside. Now that the beekeeping industry has to rely on
pesticides to control varroa, it will be under the same pressures regarding pesticide use
faced by the rest of agriculture in New Zealand.
10.2 What is integrated pest management?
One of the ways New Zealand and other countries have been able to reduce pesticide use
is through a technique called ‘integrated pest management’ (IPM). Traditional pest
control involved applying chemicals at a prescribed time, regardless of whether the pest
was actually present. IPM is different because it applies controls only when the pests are
present, and uses a variety of suitable techniques to keep pest populations below the
level where they cause economic damage. For a technique to be considered suitable, it
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should be inexpensive, cause few or no chemical residues, not result in pest resistance,
and not cause environmental damage.
Integrated pest management (IPM) uses a variety of techniques to keep
pest populations below a level where they cause economic damage.
IPM is already in use in New Zealand beekeeping for American foulbrood (AFB) control,
although it is usually not referred to as an IPM programme. The programme consists of
monitoring hives for the presence of AFB, destroying affected material, sterilising
equipment, and managing colonies to avoid the spread of AFB.
10.3 Economic threshold
A basic concept used in IPM is the ‘economic threshold’. The economic threshold of a
pest is the population level where the pest begins to cause a level of economic damage
that is greater than the cost of controlling the pest.
The economic threshold for a pest is the population level where the pest
causes significant economic damage.
The threshold can vary according to the pest or disease, or the tolerance an export
market has for the presence of the pest. For example, one cell of AFB means the hive
must be destroyed, but the presence of a single varroa mite in a hive is actually of very
little significance, unless of course it has never been reported in the area before. A
mite’s presence is not a reason to treat a colony, as by itself it will not cause any
detectable damage.
In an IPM programme, the time to treat a colony is when the population of varroa
reaches a level where it is causing economic levels of damage, or more correctly where
the population will have reached this level before the beekeeper visits the colony again.
Unfortunately, we do not have good information about the population development of
varroa in honey bee colonies under New Zealand conditions (especially in relation to
climate and length of brood rearing season), or the mite population level at which our
colonies begin to experience economic levels of damage.
Until such figures are determined through experience and research, beekeepers in New
Zealand should use the threshold figures that have been developed overseas. These
thresholds are discussed in detail in chapter 5 for each detection method. There is
some dispute about the mite population level that causes significant damage, however.
Some researchers say 2500 mites, while a US study in a climate similar to the north
half of the North Island suggests 3200. Nevertheless, until we have better information,
2500 mites in a colony should probably be taken as the threshold level under New
Zealand conditions. Remember that when using a method that surveys a sub-sample of
bees or brood in the hive, the number of mites in the sample has to be multiplied by a
conversion factor to determine the total number of mites in the hive (see appendix 1).
Economic threshold levels for varroa are discussed in detail in chapter 5.
10.4 Monitoring
While the goal of any IPM programme is to reduce pesticide use, there is always a tradeoff,
since more labour needs to be invested in monitoring to determine when the pest
CONTROL OF VARROA: INTEGRATED PEST MANAGEMENT
INTEGRATED PEST
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reaches an economic threshold. The way to make good IPM varroa control decisions in
a beekeeping outfit is to routinely sample at least a portion of the hives in each apiary
for mites.
CONTROL OF VARROA: INTEGRATED PEST MANAGEMENT
In order to make good IPM varroa control decisions, it is important to
routinely sample at least a portion of your hives in every apiary for mites.
The various types of detection methods suitable for IPM monitoring are discussed in detail
in chapter 5. Important points to remember are to use a method that fits with other
beekeeping work, and provides accurate information. Some detection methods are very
accurate (e.g., soapy water wash), but also take a lot of time. Other detection methods are
very quick (e.g., the ether roll), but aren’t very good at determining mite levels. Use the
various conversion factors in order to work out the likely total number of mites in the hive.
Chapter 5 also gives good information on using mite numbers obtained from monitoring to
make predictions about when the mite population will reach the economic threshold level.
As time goes on, there is no doubt that New Zealand beekeepers will become quite skilled
at carrying out IPM survey work, calculating likely mite numbers, and making predictions
about when mite populations will reach the economic threshold level.
The following recommendations for varroa monitoring come from British Columbia, Canada:
• Acute stage – Where varroa has just come to an area, survey before applying spring
treatment to see if treatment is required. Survey after treatment to see if treatment
has been successful. Survey towards the end of summer to determine if a second
treatment is necessary, and survey after the treatment to determine if it has been
successful. If a spring treatment was not necessary, survey in mid-summer to avoid
colony damage before autumn treatment.
• Chronic stage – After the acute stage has passed (about 3 years) and mite population
growth is more stable (i.e., there is infrequent invasion), survey twice per year
(spring and autumn). Be prepared for years of severe infestation, followed by lulls
where varroa is easy to control, followed once again by a difficulty of control. Varroa
infestation comes in ‘waves’.
• Number of hives to survey – For hobbyists, every hive; for commercial beekeepers,
10% of hives in each apiary.
Be prepared for years of severe mite infestation, followed by lulls where
varroa is easy to control, followed once again by a difficulty to control.
Varroa infestation comes in ‘waves’.
10.5 Decision-making and control
When assessing mite numbers, the decision a beekeeper using IPM has to make is
whether the population of varroa is high enough to cause a greater economic loss than the
cost of treatment. To be able to do this, beekeepers need to accurately assess the cost of
treating colonies. This should include the cost of materials, labour and travel. In any IPM
programme, preventative (also called ‘prophylactic’) treatments are generally not
considered to be cost-effective (with the possible exception of slowing down the spread of
a pest into a new area).
In an IPM programme, only treat colonies when varroa numbers are high
enough to cause more economic damage than the cost of the treatment.
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The goal of any IPM programme should be to limit the use of controls to an economic
minimum. However, in the early stages of varroa infestation in an area (the acute stage),
caution needs to be used when making assessments of mite numbers and predicting how
populations will develop, since mite invasion from feral and untreated colonies is likely to
result in quick mite population increases. Under such circumstances, there is a role for
prophylactic treatment until invasion pressure from outside sources reduces.
CONTROL OF VARROA: INTEGRATED PEST MANAGEMENT
In the acute stage, chemical control should be used on a routine basis
until mite invasion pressure from outside sources reduces.
Once the acute stage has passed, and mite population growth in colonies is more
predictable, beekeepers ideally should try to reduce chemical control treatments to no
more than two (and hopefully one) per year.
There are also a number of factors influencing the choice of varroa control method:
• Availability – Not all of the methods used overseas are likely to be available in New
Zealand. To be able to use a pesticide legally to control varroa, it must be
registered by going through the same process as all other agricultural chemicals.
The registration process is relatively expensive. There are direct costs in having a
pesticide assessed, and an even larger cost in supplying the information necessary
for the assessment. Because of the relatively small size of our industry and the
cost of registration, some companies may decide not to register their varroa control
products in New Zealand.
• Cost – The cost of some control methods (e.g., drone trapping) may limit their
usefulness to commercial beekeepers. Because economics is usually of lesser
importance to hobbyist beekeepers, they are likely to use a wider range of
techniques.
• Residues – The need to limit pesticide residues in honey and wax will restrict the
range of pesticides that can be used and when they can be applied.
• Resistance – The need to prevent or delay resistance will influence both the
pesticides used, and how often a particular compound is applied.
• Toxicity – The toxicity of the products to the beekeeper and bees is very important,
and some beekeepers may decide not to use a chemical such as formic acid
because of the potential dangers involved.
• Environmental concerns – Most beekeepers take these concerns very seriously,
especially since environmental problems that are often out of their control can
have big impacts on their beekeeping. Beekeepers need to assess the effect of the
varroa control products used (and their disposal) on the environment.
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11. TIMING OF VARROA CONTROL
This chapter discusses in detail the various options that exist for deciding when to
apply varroa controls.
11.1 Factors affecting timing of varroa control
The timing of pest control methods is a major component in any IPM programme. In the
past, the horticulture industry relied on calendar spray programmes for pest control,
where a particular spray was applied on a certain date regardless of the size of the
pest population.
Now that more has been learned about the biology of many pests, much of commercial
horticulture has moved away from calendar spray programmes. Instead, the timing of
pesticide application is often targeted to particular stages of the pest’s life cycle, or to
when a pest has reached a certain population size. By doing this, horticulturalists have
been able to reduce both their reliance on chemical control and total pest control costs.
Timing is also important in varroa control programmes. There are a number of factors
that need to be taken into account when deciding when to treat hives for varroa.
These include:
• Number of varroa present in each hive and the surrounding bee population (ferals
and other beekeepers’ hives).
• Type of control being used.
• The need to limit residues in bee products.
• Management of the colonies.
• Timing of treatments by neighbouring beekeepers.
• Length of time before the hives can be treated again.
• Rate of varroa population growth.
• How the hives are going to be used.
11.2 Treatment programme types
There are three types of treatment programmes for varroa control. They all have their
advantages and disadvantages.
11.2.1 Prophylactic treatment
Description: Colonies that don’t have varroa, or have low varroa levels, are treated as a
preventative to reduce the effects of invasion from other colonies in the neighbourhood.
A good example of where prophylactic treatment might be used is when hives are put into
kiwifruit pollination. The beekeeper may have finished varroa control while preparing
colonies for pollination. By the time the hives are moved into orchards, they have very low
mite numbers and should not need to be treated until the following season. However, in
some kiwifruit areas colonies are placed at very high densities (up to 600 colonies per
km2). Thus, there is a significant risk of these colonies being invaded by a large number
of mites from colonies (managed or feral) where varroa has not been controlled.
Prophylactic treatments were used in the spring of 2000 in New Zealand. Colonies moved
into the Te Puke area for kiwifruit pollination that were placed within 5 km of a known
apiary infested with varroa were treated with Apistan strips paid for by the government.
CONTROL TIMING
74
This was done to reduce the chance of varroa migrating to the pollination hives and then
being taken to new, non-infested areas when the hives were removed following pollination.
Advantages: Prophylactic treatment reduces the risk of losing colonies because of invasion
of varroa from neighbouring colonies.
Disadvantages: Prophylactic treatment increases the amount of pesticide that is used, with
consequent increased control costs and the chance of residues and chemical resistance.
Many of the colonies that are treated are probably not in danger of invasion, so much of
the treatment may actually be unnecessary.
CONTROL OF VARROA: TIMING OF VARROA CONTROL
Prophylactic treatment increases control costs and the chance of
residues and chemical resistance.
11.2.2 Calendar treatment
Description: All mite-infested colonies are treated at a particular time, irrespective of
whether they have potentially damaging levels of varroa. Before treating the colonies,
no attempt is made to survey them to determine whether economic threshold levels
have been reached. Calendar treatment differs from prophylactic treatment only to the
extent that in prophylactic treatment colonies not even known to be infected with varroa
are treated.
Advantages: The method avoids the cost of surveying hives for varroa. It is the method
most likely to be successful in avoiding damage caused by varroa, since all colonies are
treated. If timed properly, calendar treatment also has a good chance of protecting
colonies during autumn mite invasion in the acute phase.
Disadvantages: The method uses large amounts of pesticides, with increased cost and
increased risks of residues and chemical resistance.
If timed properly, calendar treatment will protect colonies during autumn
mite invasion in the acute phase.
11.2.3 Treatment based on monitoring and economic thresholds (IPM)
Description: Colonies are tested for the presence of varroa, and are treated only if varroa is
present in high enough numbers that economic damage will likely be caused. This method
is similar in concept to the IPM programmes used by the apple and kiwifruit industries.
Advantages: Only colonies that need it are treated, reducing the amount of pesticide used
and the attendant costs. The reduced chemical usage reduces residue problems and the
risk of chemical resistance developing.
Disadvantages: Colony monitoring is labour-intensive and exacting. It requires higher skill
levels than the other two methods, so there is a greater chance that mistakes will be
made. At present we also do not have economic thresholds established for varroa in New
Zealand. Finally, colony monitoring may not be able to predict rapid increases in mite
populations during autumn invasion in the acute phase.
IPM treatment reduces costs, as well as chances of residues and
chemical resistance. It is more labour-intensive, however, and costly
mistakes can sometimes result.
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11.3 Reducing residues
The careful timing of treatments is an important way of reducing residues in bee
products. Not using chemical control measures while the honey supers are on hives is
obviously important for some of the products. It does, however, require a higher degree of
planning, especially in the spring. It is very important to carefully follow label directions
for whatever control product is being used, since this information is based on research
regarding the best way to limit residues.
CONTROL OF VARROA: TIMING OF VARROA CONTROL
To avoid residues in bee products, always follow the label directions on
varroa control chemicals.
11.4 Changes to management
A significant issue for some beekeepers will be adjusting their beekeeping management
programmes to the required timing of varroa control treatments. Overseas experience has
shown the necessity to carry out treatment in the late summer/early autumn to protect
over-wintering bees. This has required a change in beekeeper practice so that the honey
crop is removed earlier.
If label directions are followed and varroa control is not applied until after the honey is
removed, but there is some laxness in taking off the crop, beekeepers may find their
colonies collapsing in the autumn even though the presence of well-filled boxes made it
seem as if there was no varroa problem in the hives. It is far more important to treat on
time and use proper detection techniques to determine the varroa status of hives than it
is to delay treatment because it doesn’t fit in with time-honoured beekeeping
management practices.
Beekeepers should remove their honey crop as soon as possible
so they can begin varroa treatment before autumn invasion
pressure causes colony damage.
11.5 Co-ordinated treatments
In the past, it was possible to keep honey bees in New Zealand without too much
interference caused by the management practices of other beekeepers. Occasionally there
was competition for apiary sites and the problem of a robbed-out AFB hive.
More recently, intense competition for honey production sites (especially manuka) and
kiwifruit pollination has meant that in many areas of the North Island, at least,
beekeepers need to co-operate with each other to increase income and reduce disease
risks. The advent of varroa greatly increases the need for beekeepers to work well
together, since overseas experience shows that the most efficient varroa control is
achieved by beekeepers co-ordinating their mite treatments.
After treatment with some of the most effective varroa control substances, the level of
varroa in a colony is usually very low. Because population growth of varroa in a colony is
exponential, varroa populations build up very slowly at first, and may take considerable
time to reach damaging levels.
However, varroa can easily be transported between hives, either by the bees themselves or
by beekeepers. When this occurs, varroa levels can build up to damaging levels much
more quickly. In some cases, numbers can even increase fast enough to defeat the most
effective control measures that are put in place.
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Invading mites may come from feral colonies, or managed colonies not in a varroa
treatment programme. However, another important source of these mites is managed
colonies that are in a treatment programme where the treatments do not coincide.
One beekeeper may treat hives early in the spring and have completed the work several
weeks before a neighbouring beekeeper starts treatments. This leaves time for the hives
that were treated early to become re-infected by the hives that were treated late.
Because of the high probability of cross-infestation between hives in different apiaries, it
is very worthwhile for neighbouring beekeepers to co-ordinate their treatments. To
facilitate this, it is a good practice to contact all the beekeepers in the area in order to
come to an agreement on treatment times. In countries such as Denmark, this contact is
made through the beekeepers’ association, and in New Zealand local NBA branches could
provide a similar forum for varroa control co-ordination.
CONTROL OF VARROA: TIMING OF VARROA CONTROL
Co-ordinate your varroa control treatments with those of
neighbouring beekeepers.
A co-ordinated treatment programme is much easier when hives are not moved frequently.
Obviously moving hives for pollination or to collect honey makes the job more difficult.
The best approach may be for all beekeepers in an area to treat their hives early in the
spring before the hives are moved. It is also useful to talk to beekeepers in an area before
hives are moved in to ensure they have completed their treatment programmes.
11.6 Spring and autumn treatments
Varroa control in most countries depends on both spring and autumn varroa treatments. It
is important to have very good control in spring because the large amounts of worker and
drone brood in the hive will provide ideal breeding conditions for the mites. Not providing
a high level of control at this time can result in colonies collapsing before the autumn
treatment. At the same time, good varroa control is essential throughout the autumn
period to protect hives from invasion, especially during the acute stage.
Many beekeepers in Europe use organic products such as formic or oxalic acid as an
autumn treatment, whereas in Canada formic acid treatment is preferred in spring. The
use of organic control compounds is likely to work best in the colder parts of New
Zealand, where there is no brood rearing throughout the winter. Even if the varroa kill rate
is not high, the absence of brood throughout the winter in these areas will mean that they
cannot reproduce until the spring, immediately before the spring treatment.
Much higher varroa kill rates will be required in the autumn in warmer parts of New
Zealand, where bees rear brood throughout the winter. This may limit the use of organic
compounds in these areas, entail more treatments, or at least make it critical that the
compounds are used very effectively.
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12. CONTROL METHODS USED OVERSEAS
This chapter briefly describes varroa control methods used by beekeepers in various
places around the globe. The list isn’t exhaustive, and varroa control is evolving
rapidly because the mite is of such economic significance. However, what we have
tried to do is identify several approaches from overseas that may be of interest to
New Zealand beekeepers.
12.1 British Columbia, Canada
Varroa mite was found in British Columbia (BC) in 1990, and since then it has spread to
most areas of the province. Beekeepers there suffered some serious hive losses in the
early years mostly because they were unfamiliar with varroa control. Some of the main
reasons for the losses were:
• mite invasion of colonies after treatment;
• improper timing and use of treatments; and
• not treating hives until visual symptoms were apparent.
Varroa caused heavy hive losses in British Columbia because beekeepers
were unfamiliar with varroa control and delayed treatments until they
noticed visual symptoms of mite damage.
Beekeepers in BC now treat their hives for varroa by alternating Apistan and formic
acid. They do this to help avoid mites building up resistance to a single chemical.
Formic acid is generally used in the spring as soon as temperatures reach a minimum
of 10oC. The ability of formic acid to kill varroa is very much dependent on how well
the chemical can vaporise and transfer throughout the hive. Apistan may also be used
in the spring, particularly if bees are being moved to other Canadian provinces that
legally require Apistan treatment. Spring formic acid application also works well to
control tracheal mites.
Apistan is generally used in late summer after the crop has been harvested.
Beekeepers are encouraged to remove honey as early as possible and then treat in
order to prevent serious mite damage to over-wintering bees that are being reared by
the colonies at that time.
Apistan is used according to label directions (one strip for each 5 frames of bees in
each brood chamber). Strips are left in the hives for 6 weeks and removed.
Formic acid is applied in a variety of ways, including:
• Absorbent pads.
• Bottom boards.
• Mite wipes.
• Plastic pouches.
See appendix 2 for detailed descriptions of formic acid application methods. Canada
has led the way in developing formic acid treatments for both varroa and tracheal
mites, and so we have copied their recommendations for formic acid varroa control in
this book.
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Monitoring of mite levels is now also used in BC in an integrated pest management (IPM)
programme designed to reduce chemical use and mite control costs. Hobby beekeepers
are recommended to survey all of their colonies, while commercial beekeepers should
sample 10% of hives in each apiary (especially very large and very small colonies, and
colonies at the ends of rows that pick up drifting bees carrying mites).
CONTROL OF VARROA: CONTROL METHODS USED OVERSEAS
For IPM purposes, hobby beekeepers survey all colonies, while
commercial beekeepers sample 10% of hives in each apiary.
In areas where the mites are not thought to have established, it is recommended that
colonies are surveyed twice annually (spring and autumn).
When mites are first found in an area, beekeepers survey before applying spring treatment
to see if treatment is required, and survey after treatment to see if treatment has been
successful. They also survey towards the end of summer to determine if a second
treatment is necessary, and after the treatment to determine if it has been successful. If a
spring treatment was not necessary, they survey in mid-summer to avoid colony damage
before autumn treatment.
Once feral and untreated colonies are no longer present to act as mite reservoirs for
invasion, surveying can go back to twice per year.
Sticky boards with screens are preferred as a mite survey method. Formic acid, Apistan
and the ether roll are also used in survey work. In each case, multiplication factors must
be used to determine the total number of mites in the hive.
Economic thresholds have not been determined for varroa in BC. At one time
recommendations from California were followed. Most BC beekeepers now decide when to
treat based on the data they have gathered over years of sampling their own operations,
since climatic conditions vary considerably throughout the province.
12.2 Georgia, USA
Varroa was first discovered in the United States in 1987, and since that time it has
spread throughout the country, especially as the result of migratory commercial
beekeeping activity. Varroa control in the US was for many years confined to Apistan,
but more recently (and as a result of fluvalinate-resistant varroa developing) both
formic acid and coumaphos (Check-Mite+) have been approved for use by some
government authorities.
A significant study on economic thresholds of varroa mite populations was carried out in
Georgia, in a climate somewhat similar to the northern part of our North Island. The goal
of the research was to establish mite levels using various survey techniques so that sound
decisions could be made about the use of miticides.
To reduce bias caused by differing colony strengths, the study used standard 1 kg
broodless packages of bees with small populations of mites. Hives were divided into
apiaries and one apiary was treated with Apistan in June, another in August, another in
October, and a last acting as a control (no treatment). Mite populations were surveyed at
the treatment times, using both sticky boards (natural mite drop) and ether roll. Hives
were dismantled in December (winter), and total mite populations assessed.
The results suggest that for first-year colonies in this climate (with prolonged brood
rearing), a single miticide treatment in the summer (making sure not to contaminate
CONTROL OVERSEAS
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honey) is possibly not enough to reduce mite levels sufficiently to prevent damage to the
colonies. However, a second (autumn) treatment is required only if mites have reached
the economic threshold.
CONTROL OF VARROA: CONTROL METHODS USED OVERSEAS
In warm climates with prolonged brood rearing, a single treatment may
not be enough to reduce mite levels below damaging levels.
The economic threshold at the end of summer (August) was determined to be about 3200
mites (total mite population in the hive), higher than the threshold level set in the UK
(2500). The Georgia total hive threshold equates to 15 mites on a 300 bee sample using
the ether roll, and 117 mites overnight (18 hours) for natural mite fall on sticky boards.
Sticky boards were found to be a more reliable predictor of total mite populations than
the ether roll.
Interestingly, continuous miticide treatment of colonies did not result in greater bee or
brood amounts than colonies treated two times per year.
12.3 Arizona, USA
Since 1994, researchers and beekeepers in Arizona have been involved in a co-operative
programme to see whether it is possible to develop a local population of varroa-tolerant
honey bees, using selective breeding and normal beekeeping practice but without the use
of any other mite control techniques.
Their work suggests that it is fairly easy to create a varroa-tolerant strain, with selected
stock having survived for 6 years with low annual infestation rates remaining constant at 6
to 7 mites per 100 bees. Colonies in the area originally had 120 mites per 100 bees.
Varroa tolerance can be developed in honey bee stocks using simple bee
breeding techniques.
The mechanisms of varroa tolerance were not studied in the Arizona project. They
concentrated instead on beekeeping outcomes – a honey bee stock that can live with a
low level of varroa infestation.
The following step-by-step programme has been offered to beekeepers in other parts of
the world as a recipe that can be used to develop a varroa tolerant strain. Under Arizona
(hot, dry) conditions, the programme developed varroa tolerance in two years.
Step 1 – Identify varroa-tolerant colonies.
This can be done in several ways, including:
• Leaving colonies or whole apiaries untreated (a risk, but may be worth doing as a
beekeeper group project).
• Selecting hives in the autumn before miticide treatment that have good brood
patterns, few worker cells with mite faeces, few drone brood with mites, few bees
with deformed wings, or few dead mites on the bottom board.
• Accepting untreated hives that may be abandoned or are given away and haven’t
been treated for 12 months.
• Finding hives or sites that have unintentionally been missed at treatment time the
previous year.
The Arizona work suggests that 3-10% of hives in an apiary may show some varroa
tolerance. To begin the programme, at least 10 good survivor hives are required.
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Step 2 – Put the varroa-tolerant colonies in a test apiary.
This apiary needs to be isolated (about 5 km away) from other managed hives that
are being treated to control varroa. This is done to keep drones produced by
possibly varroa-susceptible colonies from mating with varroa-tolerant virgin queens,
although the researchers say they are unsure that such mating actually reduces
varroa-tolerance. Don’t worry about drones from feral colonies, since there is a
natural selection process at work with feral colonies for varroa tolerance.
Step 3 – Monitor varroa levels.
Use the soapy water/alcohol wash technique (see section 5.3.5) to sample 100
bees from every hive every 3 months. Wash the bees with a spray attachment to
ensure all mites are removed from the bees.
Step 4 – Produce queens from colonies with low mite levels.
Remove any colonies from the apiary with more than 15 mites per 100 bees by
requeening them with queens raised from colonies with less than that number. As
the years progress, reduce this down to 10 mites per 100 bees or less. Also make
sure not to use poor producing colonies, or ones that show high aggression. Mate
all the queens in the isolated apiary. Mark the queens to ensure that the colonies
on test aren’t headed by supersedure queens. It is also worthwhile putting drone
comb in selected colonies so there are good populations of selected drones
available for mating.
CONTROL OF VARROA: CONTROL METHODS USED OVERSEAS
In an apiary of commercial size, 3-10% of hives may show some
varroa tolerance.
Requeen hives that have more than 15 mites per 100 bees with
queens raised from colonies with less than that number.
Step 5 – Re-queen other hives from queens produced in this apiary
Use the isolated apiary to produce further queens for requeening other apiaries. Requeen
all the colonies in an apiary at the same time, and then evaluate these colonies
(as above) to increase the number of colonies to select from in further generations.
Mark the queens. Move selected colonies back to the isolated apiary.
Using this system, a 600 hive outfit was totally requeened in a two-year period with
selected queen stocks. In the first year, 25% of the outfit didn’t need to be treated with
miticides, based on a mite population survey in the autumn. In the next autumn, only
about 6% of the outfit showed signs of significant varroa damage (deformed wings,
parasitic mite syndrome, and rapid bee population decline).
12.4 United Kingdom
Varroa was first discovered in the UK in 1992. Movement controls were imposed on a
county by county basis, with free movement within the infected area, but no colonies
moved into non-infected areas. According to government authorities, the idea was to slow
the inevitable spread of the mite northwards through the country. By 1999 the mite had
spread throughout England and Wales, and it has now also been found in Scotland.
Beekeeping in the UK is almost entirely hobbyist in orientation, but the finding of varroa
there has energised both beekeeping and government beekeeping services. Excellent
CONTROL OVERSEAS
81
pamphlets have been produced on managing varroa and monitoring and forecasting mite
populations. The National Bee Unit is part of the Ministry of Agriculture, Fisheries and
Food’s Central Science Laboratory, and the Unit maintains a network of regional and
seasonal bee inspectors to provide advice and assistance on mite control and other
matters. The Unit also works with a Bee Health Advisory Panel of independent
beekeeping and science experts, including representatives of the national beekeeping
organisations, to review bee disease programmes.
CONTROL OF VARROA: CONTROL METHODS USED OVERSEAS
The finding of varroa in the UK has energised both beekeeping
and government beekeeping services.
Two varroa control products are registered for use in the UK – Apistan and Bayvarol. Both
products are allowed to be applied during honey flows, although this is not recommended
unless there is a significant mite problem in the hive. Currently none of the essential oils
or organic miticides such as formic acid are registered, but veterinary authorities
acknowledge the lack of suitable registered miticides and the ‘duty of care’ beekeepers
have to treat their bees. So unregistered products are used, but they cannot be provided
to others for mite control and cannot be used if they are likely to be harmful to human
health when present in bee products.
The UK has developed a sophisticated integrated pest management (IPM) programme for
varroa control, based on mite monitoring (natural mite fall and inspecting capped brood
are the preferred methods), a series of calculations and correction factors (including
estimations of colony brood amount and bee population), and a prediction table that
estimates the number of days before mite populations reach 2500 and the colony
therefore requires treatment. Details of the UK thresholds are given in chapter 5. The IPM
programme relies on a varroa population computer model developed by the Central
Science Laboratory. The model is being refined as a result of new data, and is being used
to predict the results of various approaches to varroa control.
Biotechnical methods are also suggested as an alternative to miticide controls, and
extension pamphlets provide descriptions of different methods and explain the pros and
cons of each approach.
Workers in the UK have developed a sophisticated integrated
pest management programme for varroa control.
Finally, as a recipe for beekeepers who don’t want to carry out monitoring activities or use
biotechnical methods, the recommendation is to treat all colonies on a preventative basis
early in the spring and then in summer after the honey is removed. Once local losses have
stabilised (the acute phase is over), a single autumn treatment may be enough. UK
experience suggests that during the acute phase it is essential to treat hives quickly at the
end of summer, even if honey supers have to be removed earlier than in the past.
Beekeepers who waited to treat until after the traditional time they took honey supers off
often saw their colonies collapse due to invasion pressure.
During the acute phase, beekeepers in the UK found that it was
essential to treat hives for varroa at the end of the summer, even if
honey supers had to be removed earlier than in the past.
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82
12.5 Denmark
Denmark is often given as an example of a successful varroa control programme that
doesn’t use synthetic chemicals (such as fluvalinate, flumethrin, amitraz, coumpahos)
that are prevalent elsewhere in Europe. Bayvarol (flumethrin) is available for mite control
in Denmark on veterinary prescription, but according to a survey conducted in the country
in 2000, 86% of the beekeepers (who keep 78% of the country’s total hives) use
‘biological’ methods (organic chemicals and biotechnical controls).
Denmark has 4,600 beekeepers and 155,000 hives. Average production is similar to New
Zealand’s, at about 35 kg per hive. Varroa was first discovered in Denmark in 1984 and is
now spread throughout the country, including on most off-shore islands.
In 1984, the Danish Institute of Agricultural Sciences (Ministry of Food) proposed a
varroa control strategy that did not rely on veterinary drugs. The proposal was later
approved by the Danish Beekeepers’ Association (DBF). Both organisations have spent
considerable time and money since developing the use of organic miticides (such as
formic acid, lactic acid and oxalic acid), as well as biotechnical controls (mostly drone
brood removal, comb trapping and heat treatment). Their objective is to maintain
pesticide use at a minimum and keep chemical residues out of honey and beeswax. The
approach follows on from their commitment not to use antibiotics to control American
foulbrood, a similarity they have with New Zealand beekeepers.
CONTROL OF VARROA: CONTROL METHODS USED OVERSEAS
Denmark is an example of successful varroa control using
organic chemicals and biotechnical methods.
The Danish system can be summarised as follows:
• Drone brood removal/trapping during the late spring/early summer build-up period.
• Short and/or long-term formic acid treatment immediately following the honey
harvest.
• A late treatment once brood rearing has ceased, using either lactic acid or oxalic
acid.
• Monitoring natural mite fall, and mite fall after treatment, especially in the
summer and after lactic acid treatment in autumn.
The system also includes variations for early and late honey production, since some
beekeepers produce ling heather honey at the end of summer or beginning of autumn.
Monitoring is usually done with mesh screens on the bottom board of each hive. Daily
natural mite fall (for colonies with the equivalent of at least one frame of brood) is
multiplied by 120 to give the total number of varroa in the colony. If total mite numbers
rise above 1000, control is carried out as soon as possible.
An interesting drone brood trap used in Denmark consists of a frame divided vertically
into three sections. The frame (without foundation) is inserted into the centre of the brood
nest once the colony and conditions are good enough for comb drawing. When the bees
finish drawing out the frame with drone comb, two sections are removed, and then a week
later one of the rebuilt sections is removed again. This provides by the third week a single
comb with three different stages of drone brood development. Once a section of brood is
capped, it is removed and destroyed (usually up to the beginning of the honey flow).
CONTROL OVERSEAS
83
Nucleus colonies are made to increase numbers and for swarm control, and drone brood
trapping is used in these circumstances to take advantage of broodless situations and the
attraction that a frame of larvae has to mites looking to reproduce.
When the honey flow is over, the honey is removed and hives are treated with formic acid
in a fibre-board square sealed into a heavy-duty plastic bag. A 16 mm hole is cut in each
side of the bag. The board is left in the hive for either one or two weeks.
The colony is then given a feed of sugar syrup for over-wintering, and a second formic
acid treatment is applied for another week (provided mite fall during the previous
treatment was more than 50-100 mites). Mite fall is assessed during both treatments to
ensure temperature conditions are sufficient for the formic acid to evaporate properly and
kill mites in the hive. In some areas, beekeepers also try to co-ordinate their formic acid
applications to improve reduction of mite populations in all colonies in the vicinity.
However, re-invasion of mites is sometimes noticed, and so once the hives have become
broodless in late autumn colonies are often treated with a 15% dilution of lactic acid
sprayed on to each frame side with a garden sprayer. Each side receives 5 ml, and
treatments are repeated until fewer than 50-100 mites fall from the last treatment. If
mite numbers are low, sometimes the late lactic acid treatment is not carried out.
Oxalic acid has so far not been approved for use in the European Union, but is
nevertheless in use in countries such as Denmark. The best recommendation is to use the
substance mixed in sugar syrup. This is trickled on the bees between the combs.
Temperatures at the time of application need to be above 0oC. Rubber gloves and goggles
should be worn. Repeated treatments can cause damage to the bees, and the presence of
sealed brood will reduce effectiveness (since the material does not kill mites in the cells).
CONTROL OF VARROA: CONTROL METHODS USED OVERSEAS
Oxalic acid in sugar syrup trickled over the top bars is now
being used in Europe as a varroa control in the autumn.
For late honey flows, the formic acid treatment is either not done or is done later in the
autumn. One treatment of lactic acid or oxalic acid is sometimes substituted for this
formic acid treatment. A repeat with lactic acid only is carried out if more than 50-100
mites fall as a result of the previous treatment.
A survey of Danish honey and beeswax showed the organic chemical treatment
programme was effective in keeping miticide residues out of bee products. No miticide
residues were present in 43 samples of Danish honey. One sample was found with a
residue of a miticide that had not been in use in Denmark for 10 years. The suggestion
was that the residue, like several wax samples showing fluvalinate contamination, came
from imported beeswax.
12.6 Vietnam
Vietnam provides an interesting example of long-term success in controlling varroa
without the use of chemicals. Varroa is indigenous in Vietnam, and is a natural parasite of
Apis cerana there. It is also, however, a major pest of A. mellifera, which has been kept in
the country since the early 1960s. There are currently over 100,000 A. mellifera hives in
Vietnam, and most are kept by commercial beekeepers (the average hive holding is about
500 hives).
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84
It is actually difficult to give a total number of A. mellifera hives for either Vietnam as a
whole or for individual beekeepers, because their strategy for mite control involves
reducing colony numbers at the end of the beekeeping season (the beginning of the rainy
season), and then increasing them again at the beginning of the season (the beginning of
the dry season). Their system controls both varroa and Tropilaelaps clareae, another mite
that has crossed over to A. mellifera from its original host (A. dorsata).
Once the dry season begins, beekeepers move their hives from crop to crop for a series of
pollen and honey flows (there is very little honey produced from wild plant species), and
the first of these flows is used to make splits. Beekeepers often carry over only 50-100
colonies through the rainy season, but then split ultimately to 500 hives during the active
beekeeping year. Interestingly, annual honey yields are quite similar to New Zealand’s, at
about 30 kg per hive, based on the total number of splits finally made.
The splitting and rapid build-up means that honey bee colonies literally ‘out-breed’ the
varroa in the hives, so that varroa populations don’t have a chance to cause economic
damage until the beekeeping season has ended. The beekeepers then reduce their hive
numbers back down to a ‘foundation’ stock of 50-100 hives, making sure to select only
the best colonies to bring through the rainy season.
CONTROL OF VARROA: CONTROL METHODS USED OVERSEAS
Vietnam is a pioneer in developing biotechnical methods for
control of parasitic bee mites.
During the rainy season, the beekeepers also practice biotechnical control. Frames of
worker comb often have the bottom corners cut out in a triangle shape, and these are
rebuilt as drone comb. When the drone brood has been capped, the triangles are removed
and destroyed at intervals of about 15 days.
The Vietnamese also use whole drone combs that they encourage the bees to produce by
putting an empty frame into a strong, well-fed colony. Sometimes a group of colonies are
maintained for this purpose, and once the frames are drawn and contain young larvae, the
frames are distributed to other colonies to act as drone traps. When the brood is capped,
the frame is taken out of the hive and the pupae are removed in a hand extractor. The
pupae are sold in markets as a food delicacy.
A third technique allows beekeepers to control varroa and Tropilaelaps (which is easier to
control, since it can only survive away from brood for several days). This technique is used
during the build-up phase of new colonies once the rainy season has ended. In one
colony, all of the brood is removed, leaving only the queen, empty combs and bees. The
first two frames of capped brood that are produced are taken from the hive, uncapped and
the pupae removed. In a second colony, the queen is replaced with a cell, and given all
the brood from the first colony. Once the new queen begins to lay, again the pupae in the
first two capped frames of brood are removed. In both cases, Tropilaelaps is killed during
the broodless period, and varroa is killed during the brood trapping.
Obviously the climate and honey flows in Vietnam are very different to those found in New
Zealand, so the Vietnamese system of increase and decrease of hive numbers probably
isn’t applicable here. However, the biotechnical control methods, including drone
trapping and hive splitting, may have a use in New Zealand conditions.
CONTROL OVERSEAS
85
MANAGEMENT PLANS TO CONTROL VARROA
This section provides detailed varroa control recommendations for beekeepers of
different sizes and types of production. The recommendations depend on how long
varroa has been present in an area.
Hobbyist beekeeper – varroa not present in area
• Survey all colonies twice annually (spring and autumn) using one of the methods
described in chapter 5.
• Seek a second opinion from an Apiculture Officer or local NBA Authorised Person
on any unusual findings, either as a result of the survey or when carrying out brood
examinations.
Hobbyist beekeeper – acute stage (varroa present for 1-3 years)
General production
• Survey all colonies, using one of the methods described in chapter 5:
- before applying spring treatment;
- after the treatment to see if treatment has been successful;
- in mid-summer to avoid colony damage before autumn treatment;
- before applying autumn treatment; and
- after the treatment to determine if it has been successful.
• Treat all colonies in the early spring at the beginning of brood rearing (August-
September), and in the autumn after all surplus honey has been removed.
• To ensure treatment begins early enough to avoid colony collapse from invasion,
take honey off as soon as possible, even if the last of the crop is still coming in.
• Use registered varroa control substances (see chapter 6), and follow the label
directions exactly.
• Use a control substance in the autumn that is different from the one used in the
spring to help avoid creating chemical resistant mites (e.g., Apistan in the autumn
and formic acid in the spring).
• Carry out a treatment (remove surplus honey first) using a registered control
substance whenever the survey shows a total mite population in the hive
equivalent to 2500 mites (see table 5.2 for threshold levels for different survey
methods).
• Check mite numbers in some hives after treatment to determine if the treatment
was effective.
Organic production
• Survey all colonies, using one of the methods described in chapter 5:
- before applying spring treatment;
- after the treatment to see if treatment has been successful;
- in mid-summer to avoid colony damage before autumn treatment;
- before applying autumn treatment; and
- after the treatment to determine if it has been successful.
• Treat all colonies in the early spring at the beginning of brood rearing (August-
September), and in the autumn after all surplus honey has been removed.
MANAGEMENT PLANS
86
• To ensure treatment begins early enough to avoid colony collapse from invasion,
take honey off as soon as possible, even if the last of the crop is still coming in.
• Use organic varroa control substances such as formic acid in the spring and oxalic
acid in the autumn (see appendices 2 and 3), and follow directions exactly.
• Use drone trapping and other biotechnical methods described in chapter 8 during
the beekeeping season.
• Carry out a treatment (remove surplus honey first) using a registered control
substance whenever the survey shows a total mite population in the hive
equivalent to 2500 mites (see table 5.2 for threshold levels for different survey
methods).
• Check mite numbers in some hives after treatment to determine if the treatment
was effective.
Hobbyist beekeeper – chronic stage (after 3 years)
General production
• Follow the same regime as for the acute stage, except survey all colonies twice
annually (early spring and early autumn).
• If the autumn survey reveals mite populations well below the equivalent of
2500 mites in a hive, an autumn treatment may not be necessary.
Organic production
• Follow the same regime as for the acute stage, except survey all colonies twice
annually (early spring and early autumn).
• If the autumn survey reveals mite populations well below the equivalent of
2500 mites in a hive, an autumn treatment may not be necessary.
Commercial beekeeper – varroa not present in area
• Survey 10% of hives in each apiary (especially very large and very small colonies,
and colonies at ends of rows).
• Survey twice annually (spring and autumn) using one of the methods described in
chapter 5.
• Seek a second opinion from an Apiculture Officer or local NBA Authorised Person
on any unusual findings, either as a result of the survey, or when carrying out
brood examinations.
Commercial beekeeper – acute stage (varroa present for 1-3 years)
General production
• Survey 10% of hives in every apiary, using one of the methods described in
chapter 5:
- before applying spring treatment;
- after the treatment to see if treatment has been successful;
- in mid-summer to avoid colony damage before autumn treatment;
- before applying autumn treatment; and
- after the treatment to determine if it has been successful.
• Treat all colonies in the early spring at the beginning of brood rearing (August-
September), and in the autumn after all surplus honey has been removed.
CONTROL OF VARROA: MANAGEMENT PLANS TO CONTROL VARROA
MANAGEMENT PLANS
87
• To ensure treatment begins early enough to avoid colony collapse from invasion,
take honey off as soon as possible, even if the last of the crop is still coming in.
• Use registered varroa control substances (see chapter 6), and follow the label
directions exactly.
• Use a control substance in the autumn that is different from the one used in the
spring to help avoid creating chemical resistant mites (e.g., Apistan in the autumn
and formic acid in the spring).
• Carry out a treatment (remove surplus honey first) using a registered control
substance whenever the survey shows a total mite population in the hive
equivalent to 2500 mites (see table 5.2 for threshold levels for different survey
methods).
• Check mite numbers in some hives after treatment to determine if the treatment
was effective.
Organic production
• Survey 10% of hives in every apiary, using one of the methods described in
chapter 5:
- before applying spring treatment;
- after the treatment to see if treatment has been successful;
- in mid-summer to avoid colony damage before autumn treatment;
- before applying autumn treatment; and
- after the treatment to determine if it has been successful.
• Treat all colonies in the early spring at the beginning of brood rearing (August-
September), and in the autumn after all surplus honey has been removed.
• To ensure treatment begins early enough to avoid colony collapse from invasion,
take honey off as soon as possible, even if the last of the crop is still coming in.
• Use organic varroa control substances such as formic acid in the spring and oxalic
acid in the autumn (see appendices 2 and 3), and follow directions exactly.
• Use the hive-splitting varroa control method and other biotechnical methods
described in chapter 8 during the beekeeping season.
• Carry out a treatment (remove surplus honey first) using an organic control
substance on every hive in an apiary whenever the survey shows a total mite
population in a hive equivalent to 2500 mites (see table 5.2 for threshold levels
for different survey methods).
• Check mite numbers in some hives after treatment to determine if the treatment
was effective.
Commercial beekeeper – chronic stage (after 3 years)
General production
• Follow the same regime as for the acute stage, except survey all colonies twice
annually (early spring and early autumn).
• If the autumn survey reveals mite populations well below 2500 mites, an autumn
treatment may not be necessary.
Organic production
• Follow the same regime as for the acute stage, except survey all colonies twice
annually (early spring and early autumn).
• If the autumn survey reveals mite populations well below 2500 mites, an autumn
treatment may not be necessary.
CONTROL OF VARROA: MANAGEMENT PLANS TO CONTROL VARROA
MANAGEMENT PLANS
88
Queen producer – varroa not present in area
• Survey 10% of support colonies (especially colonies at ends of rows).
• Be especially vigilant in seeking a second opinion from an Apiculture Officer or a
local NBA Authorised Person for anything unusual found during surveying or brood
examination, since queen shipments can easily transfer varroa to areas currently
free of the mite.
Queen producer – acute stage (varroa present for 1-3 years)
General production
• Treat all support colonies and nuc-provisioning colonies in the early spring prior to
making up nucs, and in the autumn once the nucs have been reunited.
• Use registered varroa control substances (see chapter 6), and follow the label
directions exactly.
• Use a control substance in the autumn that is different from the one used in the
spring to help avoid creating chemical resistant mites (e.g., Apistan in the autumn
and formic acid in the spring).
• Ensure substantial numbers of drone production colonies are available for queen
mating purposes, since varroa depletes drone numbers.
• Treat drone production colonies at least 40 days in advance of their use to supply
drones for queen mating (further treated colonies may need to be introduced
during the season).
• Survey drone brood for mite populations using the cappings scratcher technique
(see 5.3.3).
• Survey 10% of support colonies, using one of the methods described in chapter 5,
every other month of the active beekeeping season.
• Carry out a treatment (remove surplus honey first) using a registered control
substance on every support hive whenever the survey shows a total mite population
equivalent to 2500 mites in any hive (see table 5.2 for threshold levels for
different survey methods).
• Check mite numbers in some hives after treatment to determine if the treatment
was effective.
• Select breeder queens for hygienic behaviour and suppression of mite reproduction
(see chapter 9).
• Enter into a co-operative mite tolerance breeding programme with other
beekeepers (see chapter 12).
Organic production
• Treat all support colonies and nuc-provisioning colonies in the early spring prior to
making up nucs, and in the autumn once the nucs have been reunited.
• Use organic varroa control substances such as formic acid in the spring and oxalic
acid in the autumn (see appendices 2 and 3), and follow directions exactly.
• Avoid using formic acid on drone production colonies, since the chemical has been
shown to affect drone production.
• Ensure substantial numbers of drone production colonies are available for queen
mating purposes, since varroa depletes drone numbers.
• Treat drone production colonies at least 40 days in advance of their use to supply
drones for queen mating (further treated colonies may need to be introduced
during the season).
CONTROL OF VARROA: MANAGEMENT PLANS TO CONTROL VARROA
MANAGEMENT PLANS
89
• Survey drone brood for mite populations using the cappings scratcher technique
(see 5.3.3).
• Use the hive-splitting varroa control method and other biotechnical methods
described in chapter 8 during the beekeeping season.
• Survey 10% of support hives, using one of the methods described in chapter 5,
every other month of the active beekeeping season.
• Carry out a treatment (remove surplus honey first) using an organic control
substance on every support hive whenever the survey shows a total mite population
in a hive equivalent to 2500 mites (see table 5.2 for threshold levels for different
survey methods).
• Check mite numbers in some hives after treatment to determine if the treatment
was effective.
• Select breeder queens for hygienic behaviour and suppression of mite reproduction
(see chapter 9).
• Enter into a co-operative mite tolerance breeding programme with other
beekeepers (see chapter 12).
Queen producer – chronic stage (after 3 years)
General production
• Follow the same regime as for the acute stage, except survey all support colonies
twice annually (early spring and early autumn).
• If the autumn survey reveals mite populations well below 2500 mites, an autumn
treatment may not be necessary.
Organic production
• Follow the same regime as for the acute stage, except survey all support colonies
twice annually (early spring and early autumn).
• If the autumn survey reveals mite populations well below 2500 mites, an autumn
treatment may not be necessary.
CONTROL OF VARROA: MANAGEMENT PLANS TO CONTROL VARROA
MANAGEMENT PLANS
90
Appendix 1. Estimating mite populations in hives
A. Mites in brood
All the methods except the visual inspection of brood only provide information about the
number of mites on adult bees. When a hive is in full brood production, it is estimated
that only about 15% of mites are on adult bees. Thus, the number of mites on adult bees
in the sample has to be multiplied by a correction factor of 6 to estimate the likely total
number of mites in the hive. At other times during the production season when brood is
present, use a correction factor of three. When no brood is present, no correction factor
is needed.
B. Jars of bees
When using an adult bee survey technique that doesn’t involve a miticide and samples
only a portion of the bees (i.e., ether roll, sugar shake, soapy water wash), a rule of thumb
would be to divide the number of bees in the hive (15,000 in a full Langstroth super) by
an estimate of the number of bees in the sample.
This will give a figure that can be multiplied by the number of mites in the sample and a
mites-in-brood multiplier to determine the likely number of mites in the hive.
As an example, if the hive has one full box of bees (15,000) and the sample has
300 bees:
15,000/300 = 50
If the number of mites in the sample is 2 and the hive is in full brood production (see A.
above), then the total number of mites in the hive is:
50 x 2 x 6 = 600
C. Brood sampling
To estimate the number of mites in a colony from a sample of brood, British researchers
recommend different multipliers for drone brood (10) and worker brood (1.8). To begin,
a percentage of infestation is determined by dividing the number of cells found to be
infested by the total number of cells examined. Then an estimate is made of the total
amount of sealed brood. Use a figure of about 1000 cells for one side of a good (60%
covered) frame of capped brood. This is then multiplied by the correction factor
to determine the total mite population in the hive. The estimate should only be made in
the summer.
D. Natural mite fall
According to British researchers, the daily natural mite fall on a screened bottom board
with a sticky board in winter can be multiplied by 400 to get the total number of mites in
the hive, while in the summer the multiplication number is 30. In the early spring when
brood is expanding rapidly, and in the autumn when brood amount decreases, they say
mite fall is unreliable but estimate a multiplication factor of 100. All of these
multiplication factors include mites on brood.
estimated bees in hive
bees in sample
x mites in sample x brood multiplier = mites in hive
APPENDIX 1
91
Danish researchers, on the other hand, suggest multiplying daily mite fall by 120 to give
total varroa in a colony during the production season.
E. Whole hive sampling
If Apistan, Bayvarol or formic acid is used, assume 85% of the mites on adult bees were
killed during a 24 hour survey. So divide the total number of mites on the board by 0.85
to get the total number of mites on adult bees in the hive. Also multiply the total number
by 6 if there is substantial brood in order to determine the total number of mites in the
hive (see A. above).
F. Counting mites on sticky boards
Since varroa mites are small, a magnifying glass is recommended for mite counting.
Before beginning to count boards, it is also important to do a quick refresher on the size
and shape of varroa, and how it compares with the melittiphis mite. Retaining a sample of
both mites (e.g., laminated on a card) can be especially useful.
The method used to count mite numbers on sticky boards depends on the reason the
mites are being counted and the number of mites on the board. In most cases all that is
necessary is to estimate the number of mites. This can be done by just making a quick
count of a measured area and then multiplying it by the total area of the board.
However, if a more accurate count is needed, two different methods can be used:
• Low mite numbers – When mite numbers are low, it can be difficult to scan a board
to determine if there is a varroa on it without missing some areas. To make the
count more uniform, draw parallel lines 2.5 cm apart over a sheet of clear Perspex
that has been cut to the same size as the sticky board. The Perspex can then be
placed over the board with each pair of lines used as a guide to ensure the whole
board is assessed.
• High mite numbers – High mite numbers can also be difficult to count. The best
way to proceed is to also use a sheet of Perspex. Draw a 2.5 cm x 2.5 cm grid over
the sheet. Randomly select 25% of the squares and mark their boundaries with
another colour, or erase the lines marking the squares that are not selected. The
number of mites in the selected squares is then counted and multiplied by 4 to
estimate the total number of mites on the board. If the distribution of mites does
not appear to be reasonably even over most of the board, use the method for low
mite numbers above and count all the mites.
CONTROL OF VARROA: APPENDIX 1. ESTIMATING MITE POPULATIONS IN HIVES
APPENDIX 1
92
Appendix 2. How to use formic acid
Formic acid can be purchased as an 85% concentrate. To reduce the product down
to the recommended 65%, 3 parts of the concentrate should be mixed with 1 part
water.
A. Precautions
Read the formic acid label before using and take all recommended precautions. Formic
acid is strongly corrosive.
Avoid:
• Skin contact – Formic acid can cause skin burns.
• Eye contact – Formic acid can cause blindness.
• Ingestion – Formic acid can cause burns to the stomach and oesophagus and
damage to the kidneys.
• Breathing it in – Formic acid can cause potential harmful effects.
Read the formic acid label before using and take all recommended
precautions.
B. Operator safety
• Acid-resistant gloves must be worn.
• Goggles should be used.
• Acid-resistant apron, sleeves and boots should also be used, especially when large
quantities of formic acid are being handled.
• An air-purifying cartridge-type respirator equipped for organic vapours is
recommended when using formic acid, especially in situations where there isn’t
good ventilation.
• Have ample water and rags available in case of an accident or spill.
• Avoid using warm formic acid in hot weather. Less of the harmful vapours will be
given off when the acid is cold. It may be necessary to cool the formic acid.
• Be careful when disposing of containers. Wash thoroughly with water.
C. Avoiding residues
• Do not apply formic acid when honey supers are on hives, or during nectar flows, if
honey is to be extracted for human use.
Do not apply formic acid directly on bees or brood.
Do not apply formic acid when honey supers are on hives.
D. Application methods
Formic acid works by producing a vapour that penetrates the hive. It is important that
there is enough space between the top bars of the top super and the lid to allow the
formic acid vapour to reach all parts of the colony. Manufacturers of the Canadian product
Mite Away recommend placing the bags on thin wooden strips to elevate them slightly
above the top bars. It is also important that the formic acid is not applied directly to the
bees or brood, since it will kill them.
APPENDIX 2
93
A variety of application methods have been found to be effective. The methods use formic
acid in a manner that extends the time the fumes are in the hive, although some methods
require repeat applications at 1-3 day intervals. The four most common application
methods are:
• Absorbent pads.
• Application directly to bottom boards.
• Mite wipes.
• Plastic pouches.
Table 1 at the end of this appendix provides a summary of the four methods.
1) Absorbent pads (figure 1)
• The absorbent pads can be made up of any
material that will absorb formic acid (e.g.,
three cloth serviettes, several paper towels, a
potholder or disposable nappies).
• The material must be able to absorb 30 ml of
65% formic acid without letting any drip
through.
• Prospective material can be tested for
absorbency by using water.
• Smoke bees off an area of the top bars of the
top brood box of a colony where the pad is
going to be placed.
• Lay the absorbent pad on the top bars and
dispense 30 ml of 65% acid onto the pad.
CONTROL OF VARROA: APPENDIX 2. HOW TO USE FORMIC ACID
The material must be able to absorb 30 ml of formic acid without letting
any drip through.
The treatment needs to be reapplied at 1-4 day intervals, for a total of
five or six applications.
Figure 1 Applying formic acid using an
absorbent pad.
• If temperatures are above 25oC, or if the cluster is close to the bottom board, pads
may be placed on the bottom board instead of the top bars.
• In warm temperatures, formic acid evaporates from pads in less than 24 hours.
• The treatment needs to be reapplied at 1-4 day intervals (depending on
evaporation rate), for a total of five or six applications.
APPENDIX 2
94
2) Application directly on
bottom boards (figure 2)
Formic acid can be applied directly
on bottom boards:
• To avoid killing bees, smoke the
entrance to ensure the cluster is
above the bottom board.
• Using a measuring syringe or a
drench gun, squirt 15 ml of 65%
acid along each side rail towards
the back of the bottom board.
• The treatment needs to be
reapplied at 1-4 day intervals
(depending on evaporation rate),
for a total of five or six
applications.
3) Mite wipes
These are a type of absorbent pad similar to padding found in the bottom of styrofoam
meat trays. Mite wipes prolong the evaporation period of formic acid up to 3 days.
• Work in a well-ventilated area, preferably outdoors.
• Prepare only enough pads to use in one day.
• Place the pads to be soaked in formic acid in a plastic storage container that has
an airtight cover.
• Pour 40 ml of 65% formic acid per pad onto the pads in the container. As an
example, if the container contains 10 pads, pour on 400 ml. Let the pads soak up
the acid. Place the cover on the container.
• Use as soon as possible. Storage of pads in acid for more than 2 days can damage
the pads.
• Use the pads on hives only when the outside temperature is between 10 and 30oC.
• Before going to an apiary, remove soaked pads from the soaking container. Use
gloves or tongs. Place soaked pads in a plastic pail with a lid.
• Smoke the bees off the top bars and place a pad on the top bars of the hive.
• Position the pad close to the edge of the bee cluster at the opposite end to the hive
entrance.
• Reapply five times at 4-10 day intervals (depending on evaporation rate).
• Take out used pads from hives before new ones are applied, or after 5-10 days use.
• Do not re-use the pads.
CONTROL OF VARROA: APPENDIX 2. HOW TO USE FORMIC ACID
Figure 2 Applying formic acid directly to a bottom board.
APPENDIX 2
95
4) Plastic pouches (figure 3)
These consist of zip-lock freezer or
vegetable bags filled with absorbent
material. Pouches are a convenient
treatment method for beekeepers
with outlying apiaries because only
two trips are necessary for a full
treatment. The pouch method
extends formic acid release over a
3-4 week period.
• Put 20-30 layers of
newspaper in each 27 cm x
28 cm zip-lock bag. There
needs to be sufficient newspaper to absorb all of the formic acid. This can be
tested first by using water.
• Add 250 ml of 65% formic acid per bag.
• Seal the bags, excluding most of the air, and stack them flat in a plastic box with
an airtight lid. It is a good idea to place the plastic box in another plastic bag to
ensure it is airtight.
• Place the plastic box in a freezer for 1 or 2 days before application to any hives.
• Take the box of pouches to the apiary. Remove a pouch and cut openings
(windows) in the plastic on one side of the bag exposing the absorbent material
with formic acid (figure 3). Each window should measure 1cm x 24 cm.
- For a colony in two supers, cut out two windows at either side of the pouch.
After 10 days cut out a middle window as well.
- For a colony in one super, cut out a window in the middle of the pouch. After
10 days remove one of the side windows.
- For 4 frame nucleus colonies, use smaller zip-lock bags with half of the
amount of formic acid used for bigger hives.
• Place one pouch on the top bars or bottom board of a hive with the window facing
the bees.
• If used on the top bars, use a wooden rim or inner cover to provide enough room
for the bag without crushing and to provide evaporation space for the formic acid.
• If used on the top bars, the window openings should be oriented at right angles to
the top bars.
• In cool weather, if the clusters are mainly in the top brood box away from the
bottom board, place the bags on the top bars.
• If the bees are close to the bottom board and the temperature is reasonably warm,
the pouches can be placed on the bottom board.
As an alternative to zip-lock freezer bags, zip-lock perforated vegetable bags can be used.
To charge them with formic acid, put 250 ml of acid for every bag to be filled in a large
plastic airtight container and immerse the absorbent-filled bags in the liquid. Turn the
bags several times so that they all absorb an equal amount of acid.
CONTROL OF VARROA: APPENDIX 2. HOW TO USE FORMIC ACID
Figure 3 Cutting a window in a formic acid plastic pouch.
APPENDIX 2
96
E. When to use formic acid
• Use formic acid only when outside temperatures are between 10o and 30oC.
• Spring treatment – September and October.
• Late summer treatment – February and March.
Table 1 Summary of formic acid application methods
Method Amount used (65%) Treatments Days apart
Absorbent pads 30 ml 5-6 1-4 (based on evaporation rate)
Bottom boards 15 ml 5-6 1-4 (based on evaporation rate)
Mite wipes 40 ml 5 4-10 (based on evaporation rate)
Plastic pouches 250 ml 1 3-4 weeks duration
APPENDIX 2
CONTROL OF VARROA: APPENDIX 2. HOW TO USE FORMIC ACID
97
Appendix 3. How to use oxalic acid
Oxalic acid can be purchased in crystal form as oxalic acid dihydrate. While this form is a
powder, it actually only contains 71.4% oxalic acid, so it is important to use this
correction factor when preparing solutions. To work out the percentage (weight/volume) of
oxalic acid in a syrup solution, divide the actual amount of oxalic acid (weight of oxalic
acid dihydrate x 0.714) by the total volume of the sugar solution. One kilogram of sugar
mixed with 1 litre of water produces a syrup solution of about 1.67 litres.
A. Precautions
Read the oxalic acid label before using and take all recommended precautions. Oxalic
acid is strongly corrosive.
Avoid:
• Skin contact – Oxalic acid can cause skin burns.
• Eye contact – Oxalic acid can burn the eyes.
• Ingestion – Oxalic acid can cause cramps, vomiting and convulsions.
• Breathing it in – Oxalic acid can cause harmful effects.
Read the oxalic acid label before using and take all recommended
precautions.
B. Operator safety
• Acid-resistant gloves must be worn.
• Goggles must be used.
• A dust mask is required when handling the pure chemical to prevent the dust from
being inhaled.
• Have ample water and rags available in case of an accident or spill.
• Be careful when disposing of containers. Wash thoroughly with water.
C. Avoiding residues
• Do not apply oxalic acid when honey supers are on hives, or during nectar flows, if
honey is to be extracted for human use.
Do not apply oxalic acid when honey supers are on hives.
D. Mixing with sugar syrup
• To produce a sugar syrup with 3.2% oxalic acid (w/v), mix 1 litre of water with 1kg
of sugar. Add 75 g of oxalic acid dihydrate. Mix thoroughly.
E. Amount to use
• Use 5 ml of the sugar syrup mixture per frame of bees (bees filling the inter-space
between two frames from end to end).
APPENDIX 3
98
F. Application method
• Use a large volume syringe (150 ml).
• Take up the proper dose for the
population of bees in the hive and trickle
the syrup over the bees along the top
bars (figure 1).
G. When to use oxalic acid
• Use oxalic acid in the winter when there
is little or no brood in the hive.
• Outside temperature is not important,
although the syrup can chill the bees at
very low temperatures (below 0oC).
• Oxalic acid may not have much extended
mite-killing effect, so it is not
recommended during autumn when mite
invasion pressure is high (acute stage).
CONTROL OF VARROA: APPENDIX 3. HOW TO USE OXALIC ACID
Figure 1 Applying oxalic acid in sugar
syrup directly to a colony.
APPENDIX 3
99
Appendix 4. How to use thymol
Thymol can be purchased in crystal form, and then either dissolved in alcohol or used
directly as crystals.
A. Precautions
Read the thymol label before using and take all recommended precautions. Thymol is a
hazardous substance.
Avoid:
• Skin contact – Thymol can cause skin burns.
• Eye contact – Thymol can cause serious damage to eyes.
• Ingestion – Thymol is harmful if swallowed.
• Breathing it in – Thymol can cause harmful effects.
Read the thymol label before using and take all recommended precautions.
B. Operator safety
• Wear acid-resistant gloves.
• Use goggles.
• A dust mask is required when handling the pure chemical to prevent the dust from
being inhaled.
• Have ample water and rags available in case of an accident or spill.
• Be careful when disposing of containers. Wash thoroughly with water.
C. Avoiding residues
• Do not apply thymol when honey supers are on hives, or during nectar flows, if
honey is to be extracted for human use.
Do not apply thymol when honey supers are on hives.
D. Amount to use
• The amount of thymol used per treatment depends on the treatment method.
E. Application methods
Thymol works by producing a vapour that penetrates the hive. It is important that there is
enough space between the top bars of the top super and the lid to allow the thymol
vapour to reach all parts of the colony. Use a wooden rim above the top super of the brood
nest.
Thymol can be applied as:
• Liquid soaked into absorbent pads.
• Crystals.
APPENDIX 4
100
1) Absorbent pads (figure 1)
• The absorbent pads are made from vermiculite, the green foam used by florists.
• Cut the foam into 6 cm x 4 cm rectangles with a thickness of 0.5 cm.
• For each hive to be treated, dissolve 4 g of thymol in 4 ml of alcohol (75%).
• Stir the solution thoroughly to dissolve the thymol crystals.
• Use a large syringe to take up 8 ml of the thymol solution and deposit on the piece
of foam.
• Place two pieces of foam on the top bars at opposite corners of the brood box.
• Place the rim on the box before putting on the lid.
• Apply another 8 ml of solution to each piece of foam 2-3 times at 8 day intervals.
2) Crystals
• Use lids from plastic jars about 5-7 cm in diameter.
• For each hive to be treated put two lids on the top bars at opposite corners of the
brood box.
• Put 4 g of thymol crystal in each lid.
• Place the rim on the box before putting on the lid.
• Apply another 4 g of thymol to each lid 2-3 times at 8-day intervals.
CONTROL OF VARROA: APPENDIX 4. HOW TO USE THYMOL
Figure 1 Applying
thymol acid using an
absorbent pad.
APPENDIX 4
101
Appendix 5. Varroa chemical resistance test
This test can be used to determine mite resistance when a beehive doesn’t appear to
respond to chemical mite control. The instructions that follow refer to Apistan, but by
substituting, resistance can be tested for chemical strip products such as Bayvarol,
Check-Mite+ or Apivar.
The following materials are required to carry out the test:
• 500 ml jar with lid.
• Light metal mesh cover for the jar.
• 75 x 125 mm index card or similar.
• 9 x 125 mm piece of a new Apistan strip.
• Cup to scoop up bees.
• Freezer.
• Large funnel.
• Methylated spirits.
• Paper towel.
• Plastic or rubber gloves.
• Plastic bucket.
• Sheet of white paper.
• Stapler.
• Sugar cube.
Step 1
Staple the section of an Apistan strip to the centre of the index card. Make sure to handle
the Apistan with gloves. Place the card in the jar with the section of Apistan strip facing
inwards. Place a sugar cube in the jar.
Step 2
Shake the bees from one or two combs into an up-turned hive lid or a bucket. Scoop up 1/4
of a cup (about 150 bees) and put them in the jar, being careful not to damage the bees.
Step 3
Place a wire mesh lid over the jar to stop the bees from escaping. The holes in the mesh
should be large enough to easily let varroa through. Place the jar in a warm room in the
dark for 24 hours. Make sure the lid isn’t covered so air gets to the bees.
Step 4
After 24 hours, hold the jar about 10 cm above a piece of white paper and turn it so the
mesh lid is facing downwards. Hit the jar with the palm of the hand three times. Count the
number of mites that fall on the paper. This is the ‘initial kill’ figure used in step 8.
Step 5
Place the jar of bees in the freezer to kill them. Remove the cardboard and fill the jar halfway
with methylated spirits. This should be done outside using gloves. Remove the mesh lid
and replace with the original lid for the jar. Shake the jar vigorously for 5 minutes.
APPENDIX 5
102
Step 6
Replace the mesh lid to keep the bees in the jar. Pour the methylated spirits into a bucket
using a funnel lined with a paper towel. Refill the jar with methylated spirits, swirl the
bees around and tip the spirits into the paper towel again.
Step 7
Remove the paper towel and count the number of mites recovered. Use this number as
the ‘final kill’ figure in step 8.
Step 8
Before attempting to calculate the percentage of mites killed, add together the initial kill
and the final kill. If the sum is less than 10, there were too few mites on the bees and
you will need to carry out the test again.
To calculate the percentage of mites killed, divide the number of mites that fell on the
white paper before the bees were placed in the freezer (initial kill) by the total number of
mites recovered (both on the white paper and the paper towel). Multiply this number by
100 to get the % of mites killed by the Apistan.
CONTROL OF VARROA: APPENDIX 5. VARROA APISTAN RESISTANCE TEST
If less than 50% of the mites are killed in the jar by Apistan, the mites
may be resistant to Apistan and should be tested by a laboratory.
% kill by Apistan = initial kill X 100
(initial + final kill)
If less that 50% of the mites were killed by the Apistan, the mites may be resistant and
should be tested with a more sensitive laboratory test.
APPENDIX 5
103
Appendix 6. Regulatory and legal issues related to
movement controls
The Biosecurity Act 1993 provides for controlled areas to be declared for the purpose of
instituting movement and other controls to, amongst other things, aid in limiting the
spread, minimise the damage caused, and protect an area from, an incursion of a pest or
unwanted organism.
While a controlled area notice is in force, notice may be given by a chief technical officer
or management agency that the movement into, within, or from the controlled area of
certain organisms, organic material, risk goods or other goods specified in the notice is
restricted, regulated, or prohibited. Notice may also be given that the organisms, organic
material, risk goods or other goods specified in the notice must be subject to such
treatment and procedures as specified.
It is an offence under the Biosecurity Act 1993 to move any organism, organic material,
risk good or other good specified in a controlled area notice into, within or from the
controlled area, without the permission of an inspector or authorised person, or otherwise
than in accordance with the conditions specified in the notice.
Movement controls are subject to change as varroa spreads. Consequently, details of
current movement control conditions and zones have not been listed here. For up-to-date
information on movement control and to obtain movement control permits, contact
AgriQuality, free phone 0800 424 490, or look on the MAF website (www.maf.govt.nz).
APPENDIX 6
104
Appendix 7. Regulatory and legal issues related to
treatment
There are a number of legislative controls that impact on the treatment and control of
varroa. Some of the provisions that affect beekeepers are listed below, but this is by no
means an exhaustive list of the legislative controls that may apply.
Animal Products Act 1999
It is an offence under the Animal Products Act 1999 to use any drug, substance or
mixture of substances for the prevention or treatment of varroa unless it has been
approved for that purpose.
The Hazardous Substances and New Organisms Act 1996
Some treatments for varroa may fall within the definition of a hazardous substance for the
purposes of the Hazardous Substances and New Organisms Act 1996.
It is an offence under the Hazardous Substances and New Organisms Act 1996 to
knowingly, recklessly, or negligently possess or dispose of a hazardous substance that has
been imported, manufactured, developed, or released in contravention of the Act.
Agricultural Compounds and Veterinary Medicines Act 1997
Some treatments for varroa may constitute agricultural compounds for the purposes of the
Agricultural Compounds and Veterinary Medicines Act 1997 (ACVM Act).
It is an offence under the Agricultural Compounds and Veterinary Medicines Act 1997 to
knowingly possess any agricultural compound which has not been cleared for entry into
New Zealand in accordance with the Act, or to knowingly use an agricultural compound in
contravention of the Act.
It is also an offence under the ACVM Act to knowingly sell any animal, plant, or primary
produce that has been treated with, or exposed to any agricultural compound that is not
imported, sold or used in accordance with the provisions of the Act.
The New Zealand (Maximum Residue Limits of Agricultural Compounds)
Mandatory Food Standard 1999
The New Zealand (Maximum Residue Limits of Agricultural Compounds) Mandatory Food
Standard 1999 prescribes the maximum residue limits for agricultural compounds in
food. No person shall sell any food containing residues of an agricultural compound
unless its presence is authorised under the Standard. Where a food contains an
agricultural compound for which the maximum residue limit is not prescribed in the
Standard, a person may only sell that food if it contains residues not exceeding 0.1ppm.
At this time, no maximum residue limits have been set for any varroa control treatments.
It is an offence under the Food Act 1981 for a person to produce, prepare for sale, or sell
any food unless that food complies with all applicable food standards.
APPENDIX 7
105
SUGGESTED READING
Biology
Anderson, D; Trueman, J (2000) Varroa jacobsoni (Acari: Varroidae) is more than one
species. Experimental and Applied Acarology 24(3): 165-189.
DeJong, D (1997) Mites: varroa and other parasites of brood. In Morse, R; Flottum, K (ed)
Honey bee pests, predators and diseases, 3rd edition. AI Root; Medina, Ohio; pp 282-
327.
Donze, G; Fluri, P; Imdorf, A (1998) A look under the cap: the reproductive behavior of
varroa in the capped brood of the honey bee. American Bee Journal 138 (7): 528-533.
Fries, I (1993) Varroa biology: a brief review. In Matheson, A (ed) Living with varroa.
IBRA; Cardiff, Wales; pp 3-8.
Biotechnical control
Calis, J; Boot, W; Beetsma, J; Van Den Eignde, J; De Ruijter, A; Van Der Steen, J (1999)
Effective biotechnical control of varroa: applying knowledge on brood cell invasion to trap
honey bee parasites in drone brood. Journal of Apicultural Research 38(1-2): 49-61.
Dung, N; Tan, N; Huan, L; Boot, W (1997) Control of honey bee mites in Vietnam without
the use of chemicals. Bee World 78(2): 78-83.
Pettis, J; Shimanuki, H (1999) A hive modification to reduce varroa populations.
American Bee Journal 139(6): 471-473.
Breeding for varroa tolerance
Büchler, R (1994) Varroa tolerance in honey bees – occurrence, characters and breeding.
In Matheson, A (ed) New perspectives on varroa. IBRA; Cardiff, Wales; pp 12-23.
Erickson, E; Hines, H; Atmowidjojo, A (2000) Producing varroa-tolerant honey bees from
locally adapted stock: a recipe. American Bee Journal 140(8): 659-661.
Harbo, J; Harris, J (1999) Selecting honey bees for resistance to Varroa jacobsoni.
Apidologie 30(2-3): 183-196.
Spivak, M; Gilliam, M (1998) Hygienic behaviour of honey bees and its application for
control of brood diseases and varroa. Part II. Studies on hygienic behaviour since the
Rothenbuhler era. Bee World 79(4): 168-186.
Chemical control
Brødsgaard, C; Kristiansen, P; Hansen, H (1994) Efficacy of vegetable oils as ‘soft
chemical’ acaricides against Varroa jacobsoni infesting honey bees. In Acarology IX
International Congress of Acarology, 17-22 July 1994; pp 1-5.
[http://www.biavl.dk/vid-1.htm]
Feldlaufer, M; Pettis, J; Kochansky, J; Shimanuki, H (1997) A gel formulation of formic
acid for the control of parasitic mites of honey bees. American Bee Journal 137(9): 661-
663.
SUGGESTED READING
106
Fries, I (1997) Organic control of varroa. In Munn, P; Jones, R (ed) Varroa! Fight the
mite. IBRA; Cardiff, Wales; pp 16-21.
Imdorf, A; Bogdanov, S; Ochoa, R; Calderone, N (1999) Use of essential oils for the
control of Varroa jacobsoni in honey bee colonies. Apidologie (2-3)30: 209-228.
Kraus, B (1992) Further results on lactic acid application as treatment for varroatosis.
Apidologie 23(4): 385-387.
Ritter, W (1988) Medications registered in western Europe for varroatosis control.
Apidologie 19: 113-116.
Control programmes
Bew, M; Brown, M; Morton, J (2000) Managing varroa. Central Science Laboratory,
National Bee Unit, Ministry of Agriculture, Fisheries and Food; Sand Hutton, UK; PB
2581; 16pp.
Delaplane, K (1997) Practical science – research helping beekeepers 3. Varroa. Bee
World 78(4): 155-164.
Edwards, J (2000) Beekeeping with varroa in Denmark. American Bee Journal 140(1):
459.
Gates, J (1997) Controlling parasitic mites in honey bee colonies. British Columbia
Ministry of Agriculture, Fisheries and Food; Vernon, British Columbia; 26 pp.
Imdorf, A; Charriere, J-D; Maquelin, C; Kilchenmann, V; Bachofen, B (1996) Alternative
varroa control. American Bee Journal 136(3): 189-193.
Detection and survey techniques
Ellis, M (2000) Using powdered sugar to detect varroa. Beekeeping and Honey Bees
Newsletter. University of Nebraska Institute of Agriculture and Natural Resources.
[http://ianrwww.unl.edu/ianr/entomol/beekpg/tidings/btid2000/btdjan00.htm]
Morse, R (1999) Detecting varroa. Bee Culture 127(9): 27-29.
Economic thresholds
Calis, J; Fries, I; Ryvie, S (1999) Population modeling of Varroa jacobsoni. Apidologie
30(2-3): 111-124.
Delaplane, K; Hood, W (1997) Effects of delayed acaricide treatment in honey bee
colonies parasitized by Varroa jacobsoni and a late-season treatment threshold for the
southeastern USA. Journal of Apicultural Research 36(3-4): 125-132.
Martin, S (2000) Varroa jacobsoni: monitoring and forecasting mite populations within
honey bee colonies in Britain. Central Science Laboratory, National Bee Unit, Ministry of
Agriculture, Fisheries and Food; Sand Hutton, UK; PB 3611; 10pp.
CONTROL OF VARROA: SUGGESTED READING
SUGGESTED READING
107
Effects on bees
Ball, B (1994) Host-parasite-pathogen interactions. In Matheson, A (ed) New
perspectives on varroa. IBRA; Cardiff, Wales; pp 5-11.
Rinderer, T; De Guzman, L; Lancaster, V; Delatte, G; Stelzer, J (1999) Varroa in the
mating yard: 1. The effects of Varroa jacobsoni and Apistan R on drone honey bees; 2.
The effects of Varroa and fluvalinate on drone mating competitiveness; 3. The effects of
formic acid gel formulation on drone reproduction. American Bee Journal 139 (2): 34-
139; (3): 225-227; (4): 304-307.
Shimanuki, H; Calderone, N; Knox, D (1994) Parasitic mite syndrome: the symptoms.
American Bee Journal 134(12): 827-828.
Integrated pest management
Calderone, N (1999) Integrated pest management for varroa mites: a seasonal plan for
managing the pest. Bee Culture 127(11): 20-25.
Caron, D (1999) IPM for beekeepers. American Bee Journal 139(5): 363-365.
Thomas, H-U (1997) Practical aspects of alternative varroa control methods. In Munn, P;
Jones, R (ed) Varroa! Fight the mite. IBRA; Cardiff, Wales; pp 22-30.
Internet resources
Ecosur Alternative Varroa Control Site – a short-course for South and Central American
conditions, but still very useful, especially for New Zealand organic producers.
[http://www.apicultura.com/articles/control_varroa/curso2.htm]
UK MAFF National Bee Unit – varroa control pamphlet and other valuable varroa
reference materials.
[http://www.csl.gov.uk/prodserv/cons/bee/]
University of Florida Varroa Site – a comprehensive review of varroa.
[http://creatures.ifas.ufl.edu/misc/bees/varroa_mite.htm]
USDA Honey Bee Breeding, Genetics and Physiology Laboratory – information on
breeding for varroa resistance and great photos of varroa reproduction.
[http://msa.ars.usda.gov/la/btn/hbb/]
Varroa WWW Hub – an excellent set of links to other varroa control resources.
[http://www.iacr.bbsrc.ac.uk/res/depts/entnem/varrhub/tvarrhub.html]
Residues
Bogdanov, S; Kilchenmann, V; Fluri, P; Buhler, U; Lavanchy, P (1999) Influence of
organic acids and components of essential oils on honey taste. American Bee Journal
139(1): 61-63.
Wallner, K (1999) Varroacides and their residues in bee products. Apidologie 30(2-3):
235-248.
CONTROL OF VARROA: SUGGESTED READING
SUGGESTED READING
108
CONTROL OF VARROA: SUGGESTED READING
Resistance
Milani, N (1999) The resistance of Varroa jacobsoni to acaricides. Apidologie 30(2-3):
229-234.
Pettis, J; Shimanuki, H; Feldlaufer, M (1998) Detecting fluvalinate-resistant varroa mites.
American Bee Journal 138(7): 535-541.
Watkins, M (1996) Resistance and its relevance to beekeeping. Bee World 77(4): 15-22.
SUGGESTED READING
109
USEFUL CONTACTS
AgriQuality NZ
Level 4, 8 Pacific Rise, Mt Wellington
Private Bag 14946, Panmure
AUCKLAND
phone: 0508 00 11 22 or (09) 918-4000
fax: (09) 918 4001
internet: www.agriquality.co.nz
contact person: Murray Reid, National Manager Apiculture
e-mail: reidm@agriquality.co.nz
Horticulture and Food Research Institute of New Zealand
Private Bag 3123
HAMILTON
phone: (07) 858-4728
fax: (07) 858-4704
internet: www.hortresearch.co.nz
contact person: Dr Mark Goodwin, Apiculture Scientist
e-mail: mgoodwin@hortresearch.co.nz
National Beekeepers’ Association of New Zealand
PO Box 715
WELLINGTON
phone: (04) 473-7269
fax: (04) 473-1081
internet: www.nba.org.nz
contact person: Tim Leslie, Executive Secretary
e-mail: tleslie@fedfarm.org.nz
New Zealand Ministry of Agriculture and Forestry
PO Box 2526
WELLINGTON
phone: (04) 474-4100
fax: (04) 470-2730
internet: www.maf.govt.nz
contact person: Paul Bolger, Varroa Programme Coordinator
e-mail: bolgerp@maf.govt.nz
USEFUL CONTACTS
110
TERMS AND ABBREVIATIONS USED IN THIS GUIDE
Absconding – The abandonment of a nest or hive by a colony of bees. A natural occurrence
brought on by outside disturbance or mite infestation. More common in some races and
species of honey bee (e.g., Africanised honey bee, Apis cerana) than in others.
Acute stage – The initial stage of varroa mite infestation in a population of honey bee
colonies. Large numbers of feral colonies act as a major source of mite invasion to
managed hives. Invasion results in rapid increases in mite numbers in hives.
AFB (American foulbrood) – A brood disease of honey bees caused by the bacterium
Paenibacillus larvae larvae. Produces symptoms (larvae light brown in colour, slumped
down along the side of cell) that are similar to symptoms sometimes found in association
with parasitic mite syndrome.
Apiguard – A varroa control product using the essential oil thymol formulated into a gel.
Apilife VAR – A varroa control product incorporating thymol and other essential oils in a
vermiculite tablet.
Apis cerana – The Asian hive bee, the original host of varroa.
Apis dorsata – The giant honey bee, the original host of Tropilaelaps clareae.
Apis mellifera – The western honey bee, the honey bee species present in New Zealand.
Apistan – A varroa control product consisting of a plastic strip impregnated with
fluvalinate (a pyrethroid).
Apitol – A varroa control product using cymiazole (a systemic miticide) in a granular form
that is mixed with syrup and fed to bees.
Apivar – A varroa control product consisting of a plastic strip impregnated with amitraz (a
contact miticide).
APV (acute paralysis virus) – A virus not normally thought to cause disease symptoms in
honey bees, but which can kill adult bees in varroa infested colonies, since the mite
introduces the virus into the adult bee’s blood when the mite is feeding.
Bayvarol – A varroa control product consisting of a plastic strip impregnated with
flumethrin (a synthetic pyrethroid).
Biotechnical control – Beekeeping management techniques specifically designed to reduce
varroa levels in a colony.
Black queen cell virus – A virus causing death in queen pupae. The queen cells containing
the diseased pupae take on a distinctive dark brown to black coloration. Since the virus is
transmitted through food, it is not associated with varroa.
Check-Mite+ – A varroa control product consisting of a plastic strip impregnated with
coumaphos (an organophosphate).
Chronic stage – The stage of varroa mite infestation in a population of honey bee colonies
following the acute stage. Die-off of feral and untreated colonies results in less mite
invasion and more predictable increases in mite numbers in managed hives.
TERMS AND
ABBREVIATIONS
111
Cloudy wing virus – A virus of bees that sometimes results in loss of transparency in wings.
Spread appears to have an association with varroa.
CPV (chronic paralysis virus) – A virus that produces symptoms (crawling, shaking, and a
‘hairless black’ coloration caused by bees pulling at the hairs of the diseased bee) in bees
not infested with varroa. Increased levels of CPV have been found in bees infested with
varroa.
Deutonymph – The second of two juvenile stages of the varroa mite prior to it taking on the
adult body shape. White in colour.
(DWV) deformed wing virus – A virus that can infect honey bee pupae and result in adults
with poorly developed wings, which die soon after emergence. Appears to be associated
with varroa, although bees with deformed wings may also be caused by the direct effects
of varroa feeding on pupae rather than the virus itself.
(EFB) European foulbrood – A brood disease of honey bees caused by the bacterium
Melissococcus pluton. Produces symptoms (larvae twisted in the cell, yellowish
coloration) similar to those sometimes found in association with both half-moon syndrome
and parasitic mite syndrome.
Essential oils – Plant-derived extracts that are highly volatile and have strong,
characteristic odours. Some essential oils like thymol are varroa control compounds.
Ether roll – A technique for detecting varroa using an Agee jar and ether in the form of
aerosol engine starter. The mites stick to the side of the jar.
Exponential growth – Population growth that begins slowly and then increases more and
more quickly as time goes on.
Fat-soluable – Absorbed by fats (including beeswax).
Feeding sign – Varroa mite faeces that appear as white dots at the hind end of the prepupa
or pupa and on cell walls.
Formic acid – An organic acid used as a varroa control substance. It is highly volatile, so
must be applied in forms (bags or evaporators) that prolong evaporation.
Haemolymph – Bee blood. Distributes digested food material and receives waste products
and carbon dioxide, but does not carry oxygen.
Half-moon syndrome – A disorder of honey bees with characteristics closely resembling the
symptoms of European foulbrood and parasitic mite syndrome. It does not appear to be a
disease of honey bees, since no organism has ever been found that produces the
syndrome’s effects.
Hygienic behaviour – The uncapping and removal of dead larvae and pupae by adult bees.
Inapparent – In relation to bee viruses, not producing observable symptoms in bees (e.g.,
Kashmir bee virus).
Integrated pest management (IPM) – A pest control programme using population surveys
and other techniques to keep pest populations below a level where they cause economic
damage.
Invasion (also re-invasion) – The movement of varroa mites from an infested colony into a
non-infested one as the result of drifting workers or drones, robbing of a colony that is
weakened, or absconding.
CONTROL OF VARROA: TERMS AND ABBREVIATIONS USED IN THIS GUIDE
TERMS AND
ABBREVIATIONS
112
Isolated mating – Taking mating nucs and drone production colonies to an area where
there are few or no other colonies so the queen mating that takes place is only with
drones from the nucs and the drone production colonies.
KBV (Kashmir bee virus) – A virus that does not normally cause symptoms in adult bees,
but which exists as an inapparent infection. This virus, which is closely related to APV,
might be spread by varroa.
Lactic acid – An organic acid found naturally in various food products that is used as a
varroa control substance when sprayed directly onto bees.
Mavrik – A horticultural spray containing fluvalinate (a pyrethroid).
Melittiphis (Melittiphis alvearius) – A scavenger mite often found in beehives that is the
same colour as varroa, but is different in shape and smaller than varroa.
Mesh bottom board – An insert that goes on top of a normal bottom board; varroa mites fall
through the mesh and cannot get back into the hive. The board is a useful mite survey
method and a possible partial mite control technique.
Mite Away – A slow-release formic acid control product that consists of a plastic bag and
formic acid-soaked fibreboard.
Mite wipes – Absorbent pads similar to the padding found in the bottom of stryofoam meat
trays that are used to prolong the evaporation of formic acid for varroa control.
Miticide – A chemical that kills mites.
Nuc (nucleus colony) – A small beehive, generally consisting of four frames in a purposebuilt
box (called a ‘nuc box’). Nucs are often used in queen rearing (called ‘mating nucs’).
Nuc provisioning colonies – Colonies that are split up to make nucs.
Organic – In relation to mite control substances, chemicals found in nature.
Oxalic acid – An organic acid that is used as a varroa control substance when applied in
sugar syrup directly to colonies (usually in late autumn or early winter).
Parasitic mite syndrome – The name given to a range of abnormal brood symptoms found
in association with infections of both varroa and tracheal mite. No specific causative
organism has so far been found, although viruses may be one of the causes.
Perizin – A varroa control product using the organophosphate coumaphos that is poured
into a hive in sugar syrup to control varroa.
ppm – Parts per million.
Prepupa – A larva laying out along the bottom wall of a cell in the 24 hours prior to
pupation.
Prophylactic – Use of a disease or pest treatment for prevention, rather than control.
Protonymph – The first of two juvenile stages of the varroa mite prior to it taking on the
adult body shape. White in colour.
Pupa – (plural: pupae) – The final stage of development of the honey bee; the stage when
brood take on the adult form prior to emerging as an adult bee.
CONTROL OF VARROA: TERMS AND ABBREVIATIONS USED IN THIS GUIDE
TERMS AND
ABBREVIATIONS
113
Re-invasion – see Invasion.
Resistance – Where a pest such as varroa becomes more and more able to withstand a
pesticide that is being used, so that the chemical no longer kills most of the pest
population. Varroa has developed resistance to a range of chemical control substances.
Sticky board – A board coated with a sticky substance (e.g., vegetable oil or an adhesive)
used to survey for varroa mites. The mites stick to the board and cannot return to the
hive.
Sugar shake – A method for detecting varroa that uses icing sugar and an Agee jar. The
sugar coats the mites and makes them fall off the bees.
Synthetic – In relation to varroa control substances, chemicals not found in nature.
Systemic – In relation to miticides, working through the bee’s body rather than through
direct contact.
Threshold – In relation to a pest, the population level where the pest causes significant
economic damage.
Tolerance – In association with varroa, the ability of a honey bee colony to co-exist with an
infestation of the mite without perishing, or at least harbour a higher population of mites
without damage.
Trapping – The use of combs containing drone brood to attract varroa mites so they can
then be removed from the colony. Drone brood is 8 to 10 times more attractive to varroa
than worker brood.
Tropilaelaps clareae – An external mite, originally a parasite of Apis dorsata, that has
crossed species and become a parasite of Apis mellifera.
Varroacide – A miticide that kills varroa.
Volatile – Able to evaporate into the air, usually at normal temperatures.
CONTROL OF VARROA: TERMS AND ABBREVIATIONS USED IN THIS GUIDE
TERMS AND
ABBREVIATIONS
114
INDEX
Absconding 18, 64, 110, 111
Acute stage 31, 38, 71, 76, 85, 86, 110
AFB (American foubrood) 10, 20, 21, 59, 70, 110
Amitraz (Apivar) 55
Apicure iii, 47
Apiguard iii, 41, 45, 110
Apilife VAR iii, 41, 46, 110
Apis cerana 9, 19, 64, 65, 67, 83, 110
Apistan iii
as survey method 5, 33, 37, 40, 78, 91
in varroa control 7, 20, 21, 22, 23, 41-42, 43, 44, 52, 54, 55, 56, 67, 73, 77,
78, 81, 85, 100, 110
Apitol iii, 41, 43, 110
Apivar iii, 40, 41, 43-44, 55, 101, 110
APV (acute paralysis virus) 16, 17, 18, 20, 110, 112
Arizona, USA, breeding for varroa-tolerant bee stock 67, 79-80
Bayvarol iii, 40, 110
as survey method 5, 37, 39, 91
in varroa control 7, 41, 42, 55, 56, 81, 82, 101
Biology, varroa 13
Biotechnical control 57-63, 110
Bottom boards
as survey method 5, 36
in varroa control 46, 50, 51, 77, 93
mesh 36, 60-62
Breeding programmes, for varroa tolerance 67-68
British Columbia, varroa control in 71, 77-78
Bromopropylate (Folbex) 41, 43, 55
Brood
attraction of mites to 13, 14, 22, 24, 32, 66
effects of varroa on 13, 14, 16, 18, 19, 22
mites in 90
removal and trapping 57-58
sampling 90
Calendar treatment, varroa control 74
Capped stage
duration and varroa tolerance 64, 65-66, 68
Cappings scratcher 5, 29, 32, 59, 88, 89
Cell size and varroa control 63
Check-Mite+ iii, 40, 41, 43, 78, 101, 110
INDEX
115
CONTROL OF VARROA: INDEX
INDEX
Chemical control, varroa 7, 40-52
list of chemicals 41
synthetic versus organic 41, 44
targeting 73
Chemical safety 40
Chronic stage 36, 71, 86, 87, 89, 110
Co-ordinated treatments 75
Commercial beekeepers 23, 46, 62, 71, 72, 78, 83, 86-87
Coumaphos (Check-Mite+, Perizin) 18, 41, 43, 55, 78, 110, 112
Counting mites, methods for 91
CPV (chronic paralysis virus) 16, 111
Cross-resistance 55, 56
Cymiazole (Apitol) 43
Denmark, varroa control in 48, 76, 82
Detection
methods 30-37, 31, 39, 71, 75
why required 29
Deutonymph 14, 111
Drone brood 5, 17, 24, 25, 26, 31, 32, 33, 34, 39, 63, 64, 76, 79, 88, 89, 90
removal, elimination 57, 63, 82
trapping 57, 113
Drones, effects of varroa on 17-18
DWV (deformed wing virus) 16, 17
EFB (European foulbrood) 20, 21, 111
Essential oils 44-45, 48, 51, 110, 111
Estimating mite populations 90-91
Ether roll 31, 32, 33-34, 35, 39, 71, 78, 79, 90, 111
Exponential growth 26-28, 111
Feeding sign 14, 111
Feral colonies 7, 23, 80
and acute stage 110
and invasion 27, 76
effects of varroa on 19
Flumethrin (Bayvarol) 39, 42, 55
Fluvalinate (Apistan) 41, 41-42
resistance 55
Folbex iii, 41, 43, 55
116
CONTROL OF VARROA: INDEX
INDEX
Formic acid 41, 45, 46-48, 57, 111
Apicure 47
application 92-94
as survey method 37, 39, 78, 91
commercial beekeeper 87
gel 46, 47
hobbyist beekeeper 85, 86
in British Columbia, Canada 77
in Denmark 82, 83
in the United Kingdom 81
Mite Away 112
Mite wipes 94
operator safety 47, 50, 72, 92
plastic pouches 7, 47, 95
queen producer 88
residues 48, 92
when to use 56, 76, 96
Georgia, USA, varroa thresholds in 78
Grooming, and varroa tolerance 60, 64, 67, 68
Haemolymph 13, 14, 16, 17, 43, 111
Half-moon syndrome 20, 21, 111
similarity to EFB 111
Heat treatment, varroa control using 57, 62, 82
Hive splitting, varroa control by 58, 84
Hobbyist beekeepers, varroa control plans for 45, 72, 85
Honey production 6, 21, 22, 23
residues 52
Honey removal
and varroa control 6, 7, 85, 86, 87, 88
Hygienic behaviour, varroa tolerance and 64, 65, 68, 88, 89, 111
Icing sugar
as control method 44, 50
in survey work 35, 113
Infertility, and varroa tolerance 66, 67, 68
Invasion 8, 36, 56, 71, 73, 85, 86, 87, 111
acute stage 6, 7, 29, 31, 39, 42, 52, 74, 98
and population growth 24, 26, 27, 38, 72
effect on colonies 6, 22, 77, 81, 110
Integrated Pest Management (IPM) 69-72, 73, 111
and economic threshold 29, 70
and monitoring 70, 71, 74, 78, 81
117
CONTROL OF VARROA: INDEX
INDEX
KBV (Kashmir bee virus) 16, 21, 112
Lactic acid 41, 46, 49-50, 82, 83, 112
Management changes due to varroa 5, 6, 11, 23, 75
Management plans, to control varroa 85
Mavrik iii, 52, 54-55, 112
Melittiphis alvearius 112
compared to varroa 5, 30, 91
Mesh bottom boards 36
as a varroa control 46, 50, 51, 61
how to make 60-62
in survey work 5
Mineral oil 50
Mite Away iii, 41, 47, 92, 112
Organic acids 41, 44, 46-50, 51, 76, 81, 82, 111, 112
Organic chemicals 6, 40, 44-51, 82, 83
Organic producers, varroa control plans for 85
Organic production 41, 69, 85, 86, 87, 88, 89
Oxalic acid 41, 46, 48-49, 82, 112
application 97
mixing with sugar syrup 83, 97, 98
operator safety 49, 97
when to use 76, 82, 86, 87, 88
Parasitic mite syndrome 16, 19-21, 80, 110, 111, 112
similarity to AFB and EFB 6, 20, 110, 111
similarity to half-moon syndrome 21
Perizin 41, 43, 55, 112
Pollen traps 62
Pollination 73
Pollination, effects of varroa on 23
Population estimates, varroa 38
Prophylactic treatment, varroa control using 72, 73-74
Protonymph 14, 112
Queen isolation cages, varroa control using 60, 62, 68
Queen producers, varroa control plans for 88
118
CONTROL OF VARROA: INDEX
INDEX
Reproduction rate 15, 24, 31, 66
and population growth 24-26, 63
Residues, chemical 10, 44, 57, 69, 70, 72, 73, 74, 82, 83
amitraz (Apivar) 43
bromopropylate (Folbex) 43
fluvalinate (Apistan) 42, 55
formic acid 48, 92
how to avoid 7, 35, 51, 75
lactic acid 50
organic acids 46
oxalic acid 49, 97
thymol 45, 99
Resistance, chemical 7, 9, 10, 29, 44, 48, 51, 53-56, 54, 57, 70, 72, 74, 75, 77, 113
and Apistan 55, 101, 102
and Mavrik 54
cross-resistance 55
how to measure 56, 102
how to slow 7, 55
reasons for 53
Russia, varroa tolerant bee stocks from 67
Sampling bees 13, 29, 32, 78
how to 31
Soapy water/alcohol 32, 34, 80
Sticky boards 62
in survey work 37, 78, 91
Sugar shake 5, 30, 31, 35, 39, 90, 113
Surveillance 29, 37
Synthetic chemicals 6, 40, 41-44, 48, 51, 55, 57, 82, 110, 113
Threshold, economic 5, 10, 28, 29, 31, 33, 34, 35, 36, 37, 38, 39, 52, 62, 70, 71,
74, 78, 79, 81, 86, 87, 88, 89, 113
Thymol 41, 45, 46, 110, 111
application 99, 100
how to use 99
operator safety 44, 99
residues 45
Timing, varroa control 10, 45, 73-76, 77
Tobacco smoke 35, 39
Tolerance, varroa 53, 64-68, 80, 88, 113
Apis cerana 64
Apis mellifera 65
Arizona, USA research 79
mechanisms 64
119
CONTROL OF VARROA: INDEX
INDEX
Treatment
calendar 11, 73, 74
co-ordinated 75-76
IPM 29, 69, 71, 74
prophylactic 71, 73-74, 112
spring versus autumn 6, 39, 76
United Kingdom, varroa control in 80
Varroa destructor 9
Varroa jacobsoni 9
Varroa
acute stage 31, 38, 71, 76, 85, 86, 110
biology 13
biotechnical control of 57, 110
compared to melittiphis 5, 30, 91
chemical control of 40
chronic stage 36, 71, 86, 87, 89, 110
detection methods 30-37, 31, 39, 71, 75
deutonymph 14, 111
effects on adult bees 16-18
effects on brood 14
effects on colonies 18
effects on drones 17-18, 25
effects on feral colonies 19
effects on honey production 21-22
effects on pollination 23
finding in New Zealand 9-10
how spread 13, 26, 27
identification 29-30
invasion 8, 26, 36, 56, 71, 73, 85, 86, 87, 111
parasitic mite syndrome 16, 19-21, 80, 111, 112
population estimates 38, 90-91
population growth 24-28
preference for drone brood 5, 14, 17, 24, 25
protonymph 14, 112
reproduction 14-15, 66
reproduction rate 24, 31, 66
resistance 53-56, 54
survival away from bees 13
on adult bees 13
on honey bee brood 14
scientific classification 9
spread through world 9
tolerance 53, 64
120
CONTROL OF VARROA: INDEX
INDEX
Vegetable oil 38, 44, 50, 113
Vietnam 9, 58, 83
Viruses
APV (acute paralysis virus) 16
CPV (chronic paralysis virus) 16, 111
DWV (deformed wing virus) 16, 17
KBV (Kashmir bee virus) 16, 21, 112
Visual inspection
of bees 32
of brood 32, 90
Worker bees 17, 64
Worker brood removal 57