Brenda Ball carried out a five-year study of honeybee viruses before
Varroa arrived in Britain. Some viruses were found only at certain
times of year, others were confined to either the brood or the adults,
while others were only found in colonies affected by Nosema. After
Varroa arrived in Britain further studies showed there is a
relationship between the presence of Varroa and/or viruses and colony
survival. Colonies with Varroa, but no virus, can tolerate higher
numbers of the mite than those with virus infection. Colonies with
virus infection can survive with low numbers of mites, but colonies
with virus and higher numbers of mites will die.

Deformed wing virus has become a damaging disease since the arrival of
Varroa. Only a small proportion of infected adult bees show the
crippled wings symptom but by late summer most of the bees may have
DWV. Infected bees have reduced life expectancy and this can cause
heavily infected colonies to die during the winter.

To break the cycle of virus infection brought about by Varroa mites,
it is necessary to kill the mites. This needs to be done before the
end of summer so the colony has time to produce enough healthy adult
bees to provide the overwintering population. Brenda recommended
earlier Varroa control than most beekeepers are currently doing and
that this should be done in

* late July or early August *


[this is for a northern climate. in warmer climates it may need to be
earlier still  -- pb]

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