The grooming behavior as a Varroa-tolerance mechanism in Apis mellifera colonies from Argentina

RUSSO, RM; MERKE, J; LANDI, L; PIETRONAVE, H; FAIN H; LIENDO, MC; LANZAVECCHIA, SB; PALACIO, MA; RODRÍGUEZ, G; CLADERA, JL; SCANNAPIECO, AC

Congreso; XVIII IUSSI International Congress; 2018

Varroa destructor is the greatest threat to honey bee health worldwide. This ectoparasite mite infestation is associated with high winter mortality of Apis mellifera commercial colonies in the Americas. One mechanism limiting Varroa population growth in colonies is the ability of some honey bees to groom mites from their bodies. Several stocks of honey bees have being selected in Argentina for their Varroa tolerance. In particular, so named M lines from a subtropical region have been obtained after several years of survival without acaricide treatment. They show high proportion of fallen mites. In order to explore the contribution of grooming behavior to Varroa-tolerance, we compared two M lines (M1 and M2) and a control line (C) from the same climatic region, but not tolerant to varroosis. Ten colonies from each line were monthly evaluated. We registered population sizes, hygienic behavior, % phoretic, % fallen and % damaged mites, and % infestation in brood cells. The number of colonies that survived the winter season was higher in M than in C lines. The dynamics of Varroa infestation were similar in M and C stocks, but M lines appeared to maintain the mite loads at lower level, particularly in the beginning of the autumn season. The proportion of fallen mites appeared to be maximal in spring. M showed a higher proportion of fallen mites than C lines through the season. A high proportion of damaged mites was observed in M colonies, while C colonies showed almost absence of them. Our results show that an intense grooming behavior explain the difference in Varroa-tolerance between M and C stocks, by regulating the mite loads prior to the exponential mite population grown. The level of the mite damage appears to be a good predictor of grooming. Moreover, this trait could be used as a selection target of programs breeding for Varroa tolerant honey bees.