No evidence of queen thelytoky following interspecific crosses of the honey bees Apis cerana and Apis mellifera

The human-mediated dispersal of species over geographical boundaries can bring previously isolated sister taxa into contact. Interspecific mating between closely related species may then occur, with various outcomes ranging from hybridization to reproductive interference. In the case of the Eastern honey bee Apis cerana and the Western honey bee Apis mellifera, an additional possible reproductive outcome has been posited: interspecific sperm triggers queens to produce daughters from unfertilized eggs via thelytokous parthenogenesis. Such an outcome would go unnoticed in natural population mergers, as queens, which are polyandrous, are likely to mate with both conspecific and interspecific males. We performed reciprocal crosses between A. mellifera and A. cerana via artificial insemination, plus control inseminations of saline (five queens per species per treatment), and genetically assessed the sex and origin of any resulting offspring. Neither A. cerana nor A. mellifera queens produced viable female brood after receiving interspecific semen, indicating a high cost of interspecific mating for both species. In two A. cerana colonies headed by cross-inseminated queens, workers responded by activating ovaries and laying eggs that were mainly male but occasionally female (i.e. thelytokous, 2% of brood), despite the queen’s continued presence in the nest. We conclude that thelytoky is not a consistent response to interspecific mating by queens of A. mellifera or A. cerana. Rather, at least in A. cerana, when colonies are faced with “mis-mated” queens, it may be up to the workers to secure the reproductive future of the colony.