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Symptoms and Damage of V. destructor
An adult female, V. destructor is elliptical in shape
with a width of 1.5 mm, a length of 1.0 mm, and four pairs of legs.
Mature female mites are brown, dark brown, or cordovan (photo
A). During immature stages, the bodies of V. destructor are
light and translucent, but those attributes tend to disappear on
adult hosts. Usually, there are no obvious symptoms at low levels
of infestation. As the mite population increases, a suite of symptoms,
collectively designated parasitic mite syndrome, becomes apparent.
Initially, adult workers with damaged wings are seen (photo
B). This damage is a result of DWV (deformed wing virus), which
is introduced either directly or indirectly to the developing bee
by the mite.
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Photo C. Deteriorating brood
typical with high levels of V. destructor. |
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As the infestation rate increases, more damaged workers are seen
and otherwise healthy looking bees may be seen crawling in front
of the hive, unable to fly. This condition is also caused by a virus.
Finally, the brood begins to deteriorate, appearing to be infected
with a variety of pathogens (photo C).
Although these brood symptoms superficially resemble American and
European foulbrood, the causative organisms of those diseases have
not been identified in the deteriorating brood and treatment with
antibiotics does not eliminate the condition. As the syndrome progresses,
the worker death rate exceeds the birth rate, and most new worker
bees that do emerge are seriously impaired. As a result, the colony’s
population begins a rapid decline. From the time that a colony first
exhibits brood symptoms until its total collapse can be as little
as three weeks.
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