Evidence of autogrooming as a mechanism of honey bee resistance to tracheal mite infestation

Infestations of tracheal mites (Acarapis woodi) were measured in honey bees (Apis mellifera) whose autogrooming ability was compromised by having legs or segments of legs amputated. Bees of two stocks, one more resistant (Buck-fast) and one more susceptible to tracheal mite infestation, were tested by performing amputations on uninfested, young (0-24 h) adult bees, exposing the treated bees to mites in infested colonies,then retrieving and dissecting the bees to measure parasitism. In both stocks, bees that had mesothoracic legs amputated had greatly increased mite abundances. However,the relative increase in infestation was greater in resistant bees. Mite infestation increased as more (0 vs. 1 vs. 2) mesothoracic legs were removed. in bees with only one leg removed, mite infestations were greater on the treated side, in subsequent tests with resistant stock bees only, removing the mesotarsi resulted in infestations equalling those found when entire mesothoracic legs were removed, but amputating the four distal mesotarsomeres or the metatarsi resulted in less significant increases. Restraining rather than removing mesothoracic legs also resulted in increased infestation. Young (0-24 h) bees were more affected than older (3-4 day) bees by leg removal, indicating that a factor other than autogrooming accounts for the low susceptibility of older bees to tracheal mites. Together these results are evidence that autogrooming is an important mechanism of protection against tracheal mites, especially in bees known to have genetically-based resistance to the parasite.