Tackling varroa mites in July is the best way of helping bee swarms get through the winter, concludes Wageningen bee researcher Coby van Dooremalen in an article on PLoS One.
The end of the summer sees a switch from summer bees to winter bees. These winter bees have less to do and therefore remain fitter and live longer. Their task is to get through the winter and start the colony the following spring. But that does mean they need to live long enough to survive the winter. Infection by the varroa mite prevents that. Winter bees have shorter lives if you start pest control for varroa mites too late. The study by Van Dooremalen shows that pest control in July gives the best result. These swarms are therefore more likely to survive the winter.
The Wageningen bee group has been recommending an early start on tackling varroa mites for some time. Van Dooremalen's results underpin this advice. Furthermore, the results are supported by findings in the 2011 Bee Monitor published last week by the Dutch Centre for Bee Research. Beekeepers who tackle varroa mites in July and August have winter fatalities of 14 percent only, one third less than beekeepers who apply pest control at other times.