Simplified methods of evaluating colonies for levels of Varroa Sensitive Hygiene (VSH).
José D. Villa, Robert G. Danka and Jeffrey W. Harris
Varroa sensitive hygiene (VSH) is a trait of honey bees, Apis mellifera, that supports resistance to varroa mites, Varroa destructor. Components of VSH were evaluated to identify simple methods for selection of the trait. Varroa mite population growth was measured in colonies with variable levels of VSH in two field trials using 24 and 16 colonies. Mite population growth was significantly lower in VSH and hybrid colonies than in control (i.e., unselected) colonies. In resident brood with mite infestations below 5%, the percentage of uncapped pupal cells did not differ significantly among VSH, hybrid and control colonies, but the percentage of recapped cells was highest in VSH colonies (P = 0.03). When brood from more highly infested colonies (9-49% of pupae infested) was introduced for 40 h, VSH colonies reduced infestation more than control colonies (P < 0.01) but final mite fertility was similar (P = 0.12). When infested brood was exposed in colonies for one week, VSH colonies reduced both mite fertility (P = 0.05) and mite infestation (P = 0.02). When highly infested brood was exposed to a subset of colonies for 2 h, control colonies uncapped no or few cells while uncapping in VSH colonies was variable but on average was much higher. Mite population growth in individual colonies was negatively correlated with reduced infestation after 40-h of brood exposure and with reduced mite fertility after one week. The simpler and shorter-term measures (relative to measuring mite population growth) of uncapping, recapping, and reductions in infestation and mite fertility may facilitate selection of VSH by more bee breeders.