The data show a clear reduction in worker life span in the group of colonies that did not survive winter, as well as a higher proportion of DWV-infected bees during the period when colonies died. Both V. destructor loads in colonies and individual worker DWV loads were tied to significantly lower winter bee life spans, suggesting that they play a key role in this phenomenon.

The difference in life span observed between the two groups was particularly high between mid-November and the end of December, corresponding to the start of the period where most of the colonies collapsed.

In sharp contrast, the data show that bees from colonies that survived winter in fact had significantly higher loads of N. ceranae in November than bees from failing colonies (P 0.001), strongly suggesting that this parasite is not responsible for colony collapse in winter, at least in certain parts of Europe. 

It is conceivable that Nosema loads were higher in surviving colonies because bees from these colonies lived significantly longer (10 to 15% longer) and older bees tend to accumulate more Nosema spores (30). Nevertheless, this effect would not be strong enough to mask a positive trend between Nosema load and mortality. 

Dead or Alive: Deformed Wing Virus and Varroa destructor Reduce the Life Span of Winter Honeybees
Appl. Environ. Microbiol. 2012, 78(4):981


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Peter L Borst
Cohen Lab
VRT Room T3001
Cornell University
Ithaca, NY 14853

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Peter Loring Borst
128 Lieb Road
Spencer, NY  14883
607 280 4253

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