Beekeepers are detecting large populations of parasitic Varroa mites in their hives this fall. The Varroa mite is the most serious pest of honey bees in America. Though the mite weakens honey bees by sucking their blood, called hemolymph, they cause the most hive damage by spreading disease through the bee colony. Varroa mites reproduce inside the capped bee hive cells containing the pupa stage of developing bee brood. The parasitic mites pierce the exoskeleton of honey bees with their mouth parts to suck nutrients. The perforations caused by the mites allow entry of bacterial, fungal, and viral infections. At least 15 honey bee viruses are spread by Varroa mites. The combined effect of these honey bee diseases is known as Parasitic Mite Syndrome. Hives experiencing PMS often show reduced populations of bees as they decline and eventually collapse. One easily recognizable symptom of PMS is the existence of young bees in the hive with diminished, curled wings as the result of Deformed Wing Virus. Varroa mite populations increase steadily in bee hives anytime that bees are reproducing. Mite populations large enough to collapse colonies typically occur in the late summer and early fall. Beekeepers should measure mite populations and, if necessary, treat the hives with “soft” treatments of organic acids or essential oils.
Parasitic Mite Syndrome produces brood patterns with numerous empty cells as opposed to continuous patterns of capped cells. Some of the empty cells result from workers removing honey bee pupae that they detect having mites reproducing and developing with the bee pupae. This genetically heritable honey bee activity, known as “hygienic behavior,” is the basis for Varroa resistant honey bee stock. In today’s photo we see a brood frame from a hive showing signs of Parasitic Mite Syndrome. The brood pattern is “spotty;” a number of capped cells have been opened, and the bees are chewing out the pupae. Other hive conditions, such as American foulbrood and chilled brood, may have a similar appearance.