The Varroa mite remains the most deadly parasite of honey bees, and the control of Varroa is the most important issue in honey bee colony health. Tracheal mites pose a decreasing threat, but the Varroa mite continues to kill honey bee colonies. Varroa mites develop inside the capped brood cell with the developing honey bee pupa. During the honey bee’s development and after it emerges as an adult, the Varroa mite sucks nutrients from the bee. To access the bee’s blood, or hemolymph, the Varroa mite penetrates the honey bee’s exoskeleton with its mouth parts. The resulting wound is an entry point for numerous viruses. The viruses cause a number of honey bee diseases, and their combined effect is known as “Parasitic Mite Syndrome.” While Varroa mites can be found in all honey bee hives, colonies can withstand a low level of mites. Varroa reproduce at a relatively steady rate, unlike some other honey bee pests. Small hive beetles, for instance, reproduce in massive bursts to rapidly overwhelm a bee colony.
All attempts at controlling Varroa mites should begin with seeking lines of honey bees that have a natural resistance to mites. A heritable behavior trait of resistant honey bees is described as “Varroa Sensitive Hygiene.” Bees with this trait can detect reproducing Varroa mites and remove them along with the infected bee brood. Resistant bees also preen mites from the bodies of adult bees. These mites fall through the screens of bee hives equipped with screened bottom boards, preventing reinfestation of the hive. Beekeepers can dust the bees with powdered sugar to encourage preening. If Varroa mite levels in the hive are too high, “soft” treatments using essential oils or organic acids can be used to reduce the mite levels. Each of these measures can be used together as part of an Integrated Pest Management program. While parasitic mites have killed most feral honey bee colonies, some exist, like these bees clustered for winter in a hollow tree.