ALTERNATIVE VARROA
CONTROL
lmdorf Anton, Charrière Jean-Daniel,
Maquelin Charles, Kilchenmann Verena,
Bachofen Boris
Apicultural Department
Federal Dairy Research
Institute, CH-3097
Alternative varroa control methods have
occasionally been applied with success since the appearance of varroa. Their
advantage is, that no acaricides causing persistent
residues have to be used. In the long term a good quality of the bee, products
can be guaranteed only under this condition. It is important therefore, that as
many manufacturers of bee products as possible decide to use alternative varroa
control in the near future. The treatment concepts described below will support
them in taking their decision.
The rapid and almost world-wide
spreading of the bee parasite Varroa jacobsoni in the last years has changed
beekeeping practice. In order to avoid colony losses annual varroa treatment is
required under Central European conditions. Up to now the highly effective
pyrethroids have mainly been used. The application is simple and the amount of
work involved is reasonable. However, the future use of these products is
questionable due to the formation of resistant mites, as in
Alternative varroa control leads
the way out of this dead end; The active substances used here are either
organic acids, such as formic, lactic and oxalic acid or components of
essential oils, e.g. thymol. They are widespread in nature and some of them
also occur in honey. A treatment concept has to be followed when using these
substances. Biotechnological measures for the reduction of the varroa
population have to be combined with an optimum application of the products and
control of treatment efficiency. As for the organic acids no residue problems
should arise, when applied properly. Accumulation in wax does not occur. During
treatment with essential oils, however, residues accumulate in the wax and
subsequently evaporate to a great part. The residues in honey are small and not
important from a toxicological point of view.
The following treatment concepts
have been developed and tested in extensive investigations by Swiss and
European apicultural institutes and by various beekeepers during the last
years. Various of the described methods are applied
successfully in large and small apiaries. A number of large apiaries with
several hundred colonies have in the last years refuted the claim, that
alternative varroa control be unprofitable. The key to success is the full
integration of varroa treatment into the system of hive management.
METHODS
All important information about
carrying out the different methods and the application of the various active
substances is summarised in Tables 1 and 2. The methods are described briefly
below.
COMBINATION OF APICULTURAL MEASURES AND FORMIC ACID (SHORT TERM TREATMENT)
The experience with this method
has shown, that short term treatment alone often does
not reduce the varroa population sufficiently, and the varroa increase in the
following year, combined with small re-invasions, may reach a dangerous level
until the following treatment. It is therefore necessary to reduce the increase
of the varroa population in spring by 2 to 3 removals of drone brood or by
forming a nucleus. In order to keep the amount of work involved within
reasonable limits, these biotechnological measures have to be combined with
other beekeeping activities.
During the short-term treatment
small amounts of formic acid evaporate relatively uncontrolled within 6 to 10
hours. At the beginning of the treatment the formic acid concentration in the
hive air increases rapidly. Six hours later most of it has already evaporated.
The time and the dosage of the treatment depend a lot on the temperature and on
the hive system. When applied from above, 60% formic acid is used, whereas 85%
is necessary from below. The treatment in two blocks of two to three
applications within a week in August after the honey harvest and in the end of
September has proved efficient. The treatment efficiency obtained under these
circumstances is approximately 95%. This result is possible, because formic
acid also kills a part of the mites in the brood. The efficiency may be
controlled two weeks after the last treatment by measuring the natural mite
fall, using a bottom board with a metal lattice covering the entire hive
bottom. It is sufficient to count the mites once a week. If the natural mite
fall is above one varroa per day, another treatment with oxalic or lactic acid
must follow. Six years’ experience with this method has shown,
that follow-up treatments are necessary only after re-invasions in October.
If formic acid is applied after
the honey harvest in late summer, there will be no residue problems. In order
to avoid bee and queen losses, the indications concerning temperature and
application must be followed. In August it is an advantage to feed at the time
of the treatment.
The amount of work involved is
reduced a lot by long term treatment. The soft fibre plates (Pavatex) may be prepared
in advance, during times of less work. Joint manufacturing by several apiarists
is worthwhile. The plates are impregnated with formic acid and sealed in
plastic bags of 0.15 mm thickness. If thinner plastic is used, the plates
should be kept frozen until their use in August or stored in an airtight
plastic container. Before application the necessary evaporation holes have to
be made in the plastic with a round punching tool of 1 .5 cm diameter. The
number of holes varies according to the hive system and climate (the
microclimate of the apiary is also important) and has to be tested beforehand
by small experiments. For the treatment in August the plates are hung into the
empty honey chamber by means of a honey comb frame for 7 days. After the treatment
several plates are wrapped up together in a plastic bag and frozen. In the
September treatment the same board is provided with additional evaporation
holes and put horizontally on wooden strips of 2 cm height during 14 days.
Between the cover and the upper side of the board another two wooden strips of
2 cm are placed. An insulating cover is advantageous. For medium-size one storey
hives a distance of 5 cm between the brood combs and the board should be kept.
The treatment efficiency of this
method depends on the formic acid concentration in the hive air and on the
duration of the treatment. It can be controlled during the autumn treatment on
the basis of evaporated formic acid amount. For this purpose the board has to
be weighed before and after the treatment. If there is an evaporation of more
than 7g of formic acid per day, a treatment efficiency of more than 95% may be
expected, at 1 Og per day it
will exceed 97%. If less than 7g evaporate, the treatment efficiency will be
insufficient. In that case drone brood has to be removed 2 to 3 times in spring
or a 5-days treatment has to be carried out in the period between mid-March and
mid-April. The used plates may be applied again for this treatment. They must
be reimpregnated with formic acid up to a gross weight of 250g. The way of
application and the number of holes is the same as in September. Residue
problems should not arise, if the treatment is carried out 4 weeks before the
nectar flow.
LACTIC ACID
A single application of lactic acid in broodless colonies has an efficiency of approximately 80%. In colonies with brood. the
efficiency lies between 20 and 40% About 4 treatments per year are needed, in
order to keep the varroa population below the tolerance threshold. One application
has to be carried out in November or December, when the colonies are broodless.
The time of further treatments depends on the development of the varroa
population, the nectar flow and the management system. If the natural mite fall
amounts to 5 to 10 mites a day, another treatment has to be considered soon.
During nectar flow no treatments should be made.
All bees of a colony must be
sprayed by an atomiser with a fine jet with 5 to 8 ml of 15% lactic acid per
each comb side. Depending on the type of atomiser and the adjustment of the jet
4 to 6 pumping strokes are needed. In order to avoid overdoses, the sprayed
quantity per pumping stroke should be determined. The amount of work involved
is relatively high. Therefore the use of lactic acid is mainly suitable for
small apiaries with just a few colonies.
There are no residue problems
and queen losses. Overdoses must be avoided, above all in November,
otherwise there may be losses of bees.
Oxalic acid is used in the same
way as lactic acid. The concentration (30g oxalic acid dehydrate added to 11 of
water) and the dosage (3-4 ml per comb side), however, are different. In
broodless colonies oxalic acid has an excellent efficiency of approximately
98%. The differences in treatment efficiency between the colonies are small. In
colonies with brood an efficiency of 30-40% may be expected. The treatment in
November is therefore the most efficient one. If the natural mite fall in July
is above 1 varroa per day, a treatment should be carried out after the honey
harvest in August. If there are more than 5 varroa per day in September, a
subsequent treatment is needed. In most cases two treatments should be
sufficient. According to the present knowledge no residue problems can be
expected after the treatment in late summer and autumn, If
the necessary precautions are met during the treatment, by protecting the
respiratory system (mask), the eyes (glasses) and the hands (gloves), there
should be no risk for the applying person according to toxicologists. Inhaled
mist irritates the mucous membranes and causes a dry cough. When the treatment
is carried out in a bee house, it must therefore be well aired. As for the
bees, no. noticeable side effects have been detected with the dosage described
above.
The
amount of work involved is quite reasonable in one-storey hives. Under these
conditions three persons treat approximately 25 colonies per hour in November.
The amount of work can be
reduced by the combination of a one-week formic acid treatment or three short
term treatments in August with one oxalic acid treatment or two lactic acid
treatments in November. This method is also suitable for medium-size apiaries.
It combines the advantages of good efficiency: of formic acid in August in
colonies with brood (approximately 80%) and of oxalic and lactic acid in
broodless colonies in November (approximately 98 resp.
96%). “Kramer” plates may be used for the formic acid treatment in August. In
this case the same plates may be used for the treatment of two subsequent
groups of colonies.
APILIFE VAR
Apilife VAR consists mainly of
thymol (76%), besides eucalyptol, camphor and menthol. A vermiculite tablet, impregnated
with approximately 20g of this mixture, is placed on the brood combs from
mid-August for 3 to 4 weeks. Subsequently, the tablet is replaced by a fresh
one for another 3 to 4 weeks. With application from below, the treatment
efficiency is insufficient. The efficiency strongly depends on the thymol
concentration in the hive air, which is greatly influenced by the bee behaviour
and other factors, as e.g. the comb position (warm or cold position). If the
average daily temperature falls below 120C for long periods, the
efficiency decreases.
In Swisstype and one-storey
hives (Zander or Langstroth) a treatment efficiency of approximately 97% may be
expected under optimum conditions In Dadant and two storey hives the efficiency
is often lower (90-95%) and the efficiency variation from one colony to another
is considerable. Therefore the treatment efficiency must be controlled by
measuring the natural mite fall during the two weeks after the end of the
treatment. If it is above one varroa per day, another treatment with oxalic or
lactic acid must follow. If the drone brood is removed in the following spring,
a treatment will be necessary only at a mite fall rate of more than 3 varroa
per day If the tablet is placed too near the brood,
the latter will be removed within a radius of a few cm. Therefore, the colonies
should be fed before the treatment. During the treatment essential oil
components accumulate in the wax. A great deal of them evaporates after the
treatment. In honey residues are mostly in the range of 0.1 to 0.2 mg/kg.. Concentrations above 1.1 mg per kg alter the honey taste.
From the point of view of human toxicology, these residues are not important.
Pure thymol is applied in the
same way as Apilife VAR. 15 g of thymol are dissolved in approximately 20 ml of
ethanol and poured on a viscose sponge. After the alcohol has evaporated, the
sponge is put on the brood combs like the tablets of Apilife VAR.
CONCLUSIONS
Alternative varroa control is
not restricted to the methods described in this account Various
other combinations are possible. We do not describe further methods such as
trap combs, brood rearing stop and thermo-treatment, because a great deal of
work is involved in their application.
It is essential for alternative
varroa control, that each method be carried out
correctly. The chosen method first has to be adapted to the actual conditions
(managing system, climate and nectar flow) and must be tested with a few
colonies. Control of treatment efficiency is of great importance. Some modifications
of the described methods may be necessary. If the treatment is successful, no
controls are needed any more. Biotechnological measures reducing the growth of
the varroa population are welcome in any hive management. Thus, the number of
treatments is reduced, and the formation of varroa populations near the
tolerance threshold is prevented. Once the beekeeper has decided on switching
to alternative varroa control, he should make sure to use wax for the
production of comb foundations, which is free from residues.
Before switching to alternative
varroa control, the beekeeper should be well informed on the alternatives.
Courses on alternative varroa control organised by the beekeepers associations
might be helpful.
ACKNOWLEDGMENTS
A
number of institutes as well as many beekeepers have contributed a great deal
to the present knowledge concerning alternative varroa control Therefore we
sincerely thank especially Gerhard Liebig, Kurt Kramer, M. Krasnik, Alois
Wallner, Johann Weiss and many others for sharing with us their experiences in
various discussions and many publications. Special thanks to the many
beekeepers, who have contributed to the present knowledge by collaborating in
the experiments of our studies during the past decade. Thanks also to Barbara Bogdanov,
who translated this report into English.
REFERENCES
A reference list may be
requested from the Apicultural Department, Federal Dairy Research Institute, CH3097
Liebefeld,
The Use of Drone Brood Comb in Anti-Varroa Treatment
by ROBERT RÖNNAU
Translated from the
Schweizerische Bienen Zeitung, March 1999, page 131
by A. E. McARTHUR MIL
From the time
it was possible to purchase drone foundation from bee keeping equipment supply
houses, I have used them wired into my frames with stainless steel wire. These
frames are exactly the same as the frames used in the super and brood box. This
frame is more than a ‘building frame’. The wiring firms up the comb. The drone
foundation is drawn more readily than the strip of foundation and therefore
more rapidly available as a ‘trapping’ comb for the mites.
Each colony receives two drone combs in the spring, one on each side of the brood nest. As soon as either one or both combs are around 2/3 sealed, they are removed with adhering bees. At the same time another two drone combs fitted with foundation are inserted.
The drone combs with the
adhering bees are used either:
a)
Individually as reinforcement together with sealed worker brood.
or
b) Used to
form Nucleus stocks with up to 10 of these removed combs.
They serve as trapping combs,
since they contain as yet unsealed drone brood and the Varroa mites on the
adult bees on the sealed worker brood have nowhere else to go, other than into
the unsealed drone brood. Three or four days later these drone combs are
removed from the nuclei and placed in the solar wax extractor to retrieve the
wax. This method of operation removes the mites safely from the nucs. The nucs
are then given comb with eggs or unsealed larvae using either the method
developed by Götz or Jenner to encourage them to produce a new queen.
The strong colonies draw up to
five drone combs each. Their removal is a mild form of ‘shook swarm’ and
reduces the urge to swarm and limits the Varroa populations considerably. I
feel myself completely justified by the work done by Anton Imdorf at Liebefeld:
that drone removal reduces the potential Varroa population by as much as 50%.
Using drone combs for nucleus
building on their own or together with worker brood combs I am able to achieve
a dramatic reduction in the levels of Varroa infestation and in so doing I am
able to give each of my strong stocks either a nucleus stock as a reinforcement
or a new current year queen in the autumn.
The use of drone foundation
reduces the construction of drone cells in the corners of the worker brood frames.
The former practice of inserting foundation strips has now been superseded as
has also the use of expensive anti-Varroa treatments which at worst leave
unpleasant residues in the wax and at best result in resistant mites.