Varroa mites (Varroa destructor) spread viruses, feed on honeybee larvae and could be contributing to widespread losses of bee colonies. Beekeepers try to control the pests using chemicals; but in an 11-month study of 120 commercial colonies, Gloria DeGrandi-Hoffman at the US Department of Agriculture in Tucson, Arizona, and her colleagues revealed that 55% of treated hives were still lost.
A model that simulated varroa populations and bee interactions showed that natural swarming, which is suppressed in domesticated bees, keeps varroa populations down. That’s because swarming carries mites away from hives and reduces the number of bee larvae produced, shrinking the mites’ food supply. Furthermore, infected forager bees that raid other hives can quickly spread the mites when hives are close together.
The authors think varroa might be impossible to control unless changes are made to the way bees are kept.