Cleaning Bees Wipe Out Mites

Genetically enhanced honey bees are cleaning up on Varroa mite infestations that have devastated hives across the U.S. and threatened the bee industry.

The parasitic Varroa mite attacks the honey bee, Apis mellifera L., by feeding on its hemolymph, which is the combination of blood and fluid inside a bee. Colonies can be weakened or killed, depending on the severity of the infestation. Most colonies eventually die from varroa infestation if left untreated.

Varroa-sensitive hygiene (VSH) is a genetic trait of the honey bee that allows it to remove mite-infested pupae from the capped brood–developing bees that are sealed inside cells of the comb with a protective layer of wax.

Honey bees are naturally hygienic, and they often remove diseased brood from their nests. VSH is a specific form of nest cleaning focused on removing varroa-infested pupae.
ARS researchers have developed honey bees that more aggressively deal with varroa mites, a parasite that is one of the major problems damaging honey bees today.
Varroa mites are a major threat to honey bee health and are becoming resistant to two compounds (coumaphos and fluvalinate) used to control them. Beekeepers now have a simple assay to determine whether mites are resistant and thus ensure use of appropriate control measures.

Photo by Stephen Ausmus.

Agricultural Research Service (ARS) scientists have developed bees with a high expression of the VSH genetic trait, allowing them to more easily find the mites and toss them out of the broodnest. These bees are quite aggressive in their pursuit of the mites. They gang up, chew and cut through the cap, lift out the infected brood and their mites, and discard them from the broodnest. See video.

The cleansing kills the frail mite offspring, which greatly reduces the lifetime reproductive output of the mother mite. The mother mite may survive the ordeal and try to reproduce in brood again, only to undergo similar treatment by the bees.

To test the varroa resistance of VSH bees, the Honey Bee Breeding, Genetics and Physiology Research Unit in Baton Rouge, Louisiana, conducted field trials using 40 colonies with varying levels of VSH. Mite population growth was significantly lower in VSH and hybrid colonies than in bee colonies without VSH. Hybrid colonies had half the VSH genes normally found in pure VSH bees, but they
still retained significant varroa resistance. Simpler ways for bee breeders to measure VSH behavior in colonies were also developed in this study.

Source: Source: Agricultural Research Service