http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0057540

Abstract

Varroa mites and viruses are the currently the high-profile suspects in
collapsing bee colonies. Therefore, seasonal variation in varroa load and
viruses (Acute-Kashmir-Israeli complex (AKI) and Deformed Wing Virus (DWV))
were monitored in a year-long study. We investigated the viral titres in
honey bees and varroa mites from 23 colonies (15 apiaries) under three
treatment conditions: Organic acids (11 colonies), pyrethroid (9 colonies)
and untreated (3 colonies). Approximately 200 bees were sampled every month
from April 2011 to October 2011, and April 2012. The 200 bees were split to
10 subsamples of 20 bees and analysed separately, which allows us to
determine the prevalence of virus-infected bees. The treatment efficacy was
often low for both treatments. In colonies where varroa treatment reduced
the mite load, colonies overwintered successfully, allowing the mites and
viruses to be carried over with the bees into the next season. In general,
AKI and DWV titres did not show any notable response to the treatment and
steadily increased over the season from April to October. In the untreated
control group, titres increased most dramatically. Viral copies were
correlated to number of varroa mites. Most colonies that collapsed over the
winter had significantly higher AKI and DWV titres in October compared to
survivors. Only treated colonies survived the winter. We discuss our
results in relation to the varroa-virus model developed by Stephen Martin.

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