Selecting honeybees for worker brood that reduces the reproduction of Varroa destructor

Abstract

We investigated an effect of Apis mellifera worker brood on the reproduction of Varroa destructor as a resistance trait by conducting seven generations of bidirectional selection. Initial tests showed twofold differences in mite fecundity (progeny per foundress mites) between colonies of different origins. In the first two generations of selection, low and high lines differed significantly in mite fecundity (2.6 vs. 2.9 and 2.3 vs. 2.8), but in five subsequent generations the average values of the low fecundity lines (ranges of 2.7 to 3.3) became indistinguishable from high lines (2.9 to 3.1). Similarly, the relationship between mite fecundity in 117 offspring colonies and in their 26 queen and 22 drone parent colonies was partly significant in the first three generations but not in subsequent generations. These findings suggest that adaptation of mites to host cues, loss of resistance alleles in a small breeding population, or environmental effects present challenges to breeding for this trait.