Varroa sensitive hygiene (VSH) is a behavioral trait of honey bees (Apis mellifera) in which bees detect and remove bee pupae that are infested by the parasitic mite Varroa destructor. V. destructor is considered to be the most dangerous pest problem for honey bees worldwide. VSH activity results in significant resistance to the mites.
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Development
Bees with the trait were initially bred by the USDA Honey Bee Breeding, Genetics and Physiology Laboratory in Baton Rouge, LA from colonies in which mite populations grew only slowly.
The factor causing slow mite population growth was found to be heritable. The rate of mite population growth was found to be correlated with the reproductive rates of mites, resulting in naming the factor “suppressed mite reproduction” (SMR). It was subsequently discovered that the factor is founded on hygienic activity of adult bees, so SMR was renamed VSH.
VSH activity results in (1) an abnormally low proportion of mites that produce offspring within the population that remains in capped brood and (2) reduction of the brood infestation rate by greater than 70%. The specifics of how hygienic bees detect mite infested brood currently are unknown.
Cross-breeding
Bees bred to have high levels of VSH tend to keep mite populations below thresholds recommended for treatment with pesticides. Queens from such VSH breeding sources can be allowed to mate freely with non-VSH drones, and the resulting hybrid colonies from these outcrosses will retain lower and variable but generally still useful resistance to V. destructor while retaining desirable beekeeping traits such as honey production.
VSH outcrossed to commercial Italian bees recently have been shown to perform well in migratory crop pollination.
VSH thus is a trait that can be used by breeders to mix with any type of desirable honey bee and is expanding resistance to V. destructor among diverse bee strains. VSH breeding material has been available through commercial sources since 2001.