The long term survival of your bees depends directly on their health. 
The most serious threat to bee health is STILL varroa infestation and its effects on the individual bee and colony lifespan.

> Background: Recent elevated winter loss of honey bee colonies is a major concern. The presence of the mite Varroa
> destructor in colonies places an important pressure on bee health. V. destructor shortens the lifespan of individual bees,
> while long lifespan during winter is a primary requirement to survive until the next spring. We investigated in two
> subsequent years the effects of different levels of V. destructor infestation during the transition from short-lived summer
> bees to long-lived winter bees on the lifespan of individual bees and the survival of bee colonies during winter. Colonies
> treated earlier in the season to reduce V. destructor infestation during the development of winter bees were expected to
> have longer bee lifespan and higher colony survival after winter.
> 
> Methodology/Principal Findings: Mite infestation was reduced using acaricide treatments during different months (July,
> August, September, or not treated). We found that the number of capped brood cells decreased drastically between August
> and November, while at the same time, the lifespan of the bees (marked cohorts) increased indicating the transition to
> winter bees. Low V. destructor infestation levels before and during the transition to winter bees resulted in an increase in
> lifespan of bees and higher colony survival compared to colonies that were not treated and that had higher infestation
> levels. A variety of stress-related factors could have contributed to the variation in longevity and winter survival that we
> found between years.
> 
> Conclusions/Significance: This study contributes to theory about the multiple causes for the recent elevated colony losses
> in honey bees. Our study shows the correlation between long lifespan of winter bees and colony loss in spring. Moreover,
> we show that colonies treated earlier in the season had reduced V. destructor infestation during the development of winter
> bees resulting in longer bee lifespan and higher colony survival after winter.

Citation: van Dooremalen C, Gerritsen L, Cornelissen B, van der Steen JJM, van Langevelde F, et al. (2012) 
Winter Survival of Individual Honey Bees and Honey Bee Colonies Depends on Level of Varroa destructor Infestation. 
PLoS ONE 7(4): e36285. doi:10.1371/journal.pone.0036285

Funding: The project was funded by Ministry of Agriculture, Nature Conservation and Food Quality (LNV) of the Netherlands and by the European Union

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Peter L Borst
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