By now few beekeepers can be unaware that Varroa resistant to Apistan and Bayvarol
are spreading right across the country. So far, none has been reported in the county
but they are on the borders. It will only be a short time before they are found in
the county. This means that beekeepers should be taking at least two actions this
Firstly, each one of us should be checking to see if there are resistant Varroa in
our colonies. If you are unsure how to do this, check with Maurice Roll our bee disease
officer. Secondly, we should all be making ourselves familiar with methods of controlling
Varroa without using Apistan and Bayvarol and ensuring that we have the necessary
equipment to do this.
The posh term for this is Integrated Pest Management, or IPM. What it means is that
one should use more than one method of killing a pest and meld them together in such
a way that you have a sporting chance of keeping the pest under control.
We have to accept that it is not possible to eliminate Varroa from the UK. Nowhere
has this being done once Varroa has gained a foothold and continental countries have
being plagued with the pest for many more years that we have. So we are going to
have to continue to attempt to control Varroa. We also have to accept that if we
just use one chemical for its control then we are almost certain to have Varroa resistant
to that chemical within a few years. This is because no chemical is 100% effective
so some Varroa always survive. Those that survive have some resistance to the chemical
and as they are the ones that are left to multiply up, the resistance becomes stronger
and finally we have a pest which we cannot control.
To avoid getting into this plight with Varroa in this county we need to introduce
other methods of control NOW. The other methods available to us are either use other
chemicals or use biotechnical methods. I do not propose to write anything about other
chemicals as these are widely advertised, but be aware that those that are available
are only effective under limited conditions. None of the biotechnical methods are
fully effective but at least no amount of resistance to chemicals saves the Varroa
when they are caught by these methods! So at least for one generation the spread
of chemical resistance is slowed down.
Methods available in order of ease of use:
1. Mesh floors. Any healthy Varroa which inadvertently drop off the bees fall through
the floor onto the ground and are unable to get back up into the colony. Thus their
numbers are reduced and we will be selecting for Varroa that do not fall off bees!
2. Cutting out drone comb. Varroa prefers to parasatise drone brood and because it
takes three days longer to pupate, one or two extra mature Varroa progeny are produced
on each drone pupa than on a worker pupa. Early in the season when the bees are producing
drones then extra drone comb can be given to the colony and removed when the drone
brood is sealed in, thus removing all of the Varroa in it. This can be done by replacing
a brood comb with a super comb with worker foundation. Worker brood will be produced
in the comb and drone comb will be built on the bottom of the frame which can be
cut off when the drone brood in it is sealed. A second and third super comb can be
introduced at subsequent visits. Before the drone comb is destroyed it can be examined
to find out the intensity of the infestation. It is said that this method will keep
the infestation down to 50% of what it would otherwise have built up to.
3. Queen trapping. This method requires that the queen to be confined to one comb
for nine days and then confined to a second and third comb for further periods of
nine days. (Or it could be four periods of seven days.) The first comb is removed
before the third comb is put in as by then the brood on it will be sealed. Nine days
later the second comb is removed and the queen is freed from her cage, with the final
frame being removed nine days later. For 27 days the only brood available for Varroa
to go into is on the three introduced combs, and as all of this is removed and destroyed
a high proportion of the Varroa present in the colony will be removed. A little thought
will show why I have listed this as No 3. It requires a specialised cage of queen
excluder material, which encloses a frame, preventing the queen getting away from
it but allowing workers to get in and tend the queen and the brood, and it is labour
intensive. If the honey crop is not to be affected timing is important too. Late
June to mid-July would seem to be the best time, as by this time any brood produced
is too late to forage for this year's crop and the bees produced at this time will
be too old to over winter. Those with just a few hives should be able to manage this
method, and it is very effective.
What are you doing about resistant Varroa?
Bee-Lines (A selection from our quarterly magazine)