Pheromonal predisposition to social parasitism in the honeybee Apis mellifera capensis

In honeybees, worker reproduction is mainly regulated by pheromones produced by the brood and the queen. The source of one of the queen pheromones influencing worker reproduction has been located in the mandibular glands. In nonlaying workers, this gland's profile is dominated by fatty acids that are incorporated into the food given to the brood and to nest mates. After queen loss and onset of reproductive activity, workers are able to synthesize different fatty acids, which are normally only produced by queens and that contribute to their reproductive success. Apis mellifera capensis workers have the ability to rapidly produce queen-like mandibular profiles that could represent an important factor in their ability to behave as facultative intraspecific social parasites. Indeed, A. m. capensis workers can take over reproduction from the host queens in colonies of other subspecies. Here, we show that in the presence of their own queen, the mandibular gland profile of A. m. capensis workers is dominated by the precursor of the major compound of the queen pheromone. This is a unique trait among honeybee workers and suggests that A. m. capensis workers are primed for reproduction and that this phenomenon represents a pheromonal predisposition to social parasitism. We identified geographical variation in the ratio of queen- to worker-specific compounds in the mandibular gland profile of A. m. capensis workers, which corresponds with the introgression with the neighboring subspecies A. m. scutellata. Copyright 2010, Oxford University Press.

Worker reproduction in mixed-species colonies of honey bees

To explore reasons for the unusually high rates of worker ovary activation in Apis cerana, we investigated the reproductive physiology of workers in conspecific and mixed-species colonies of A. cerana and its sibling species Apis mellifera under queenright and queenless conditions. In both queenless and queenright conspecific colonies, the proportion of A. cerana workers with activated ovaries was significantly greater than the proportion of A. mellifera workers with activated ovaries. Apis cerana workers showed significantly greater ovary activation in queenright mixed-species colonies than in conspecific queenright colonies. Moreover, there was significantly greater ovary activation in A. cerana workers in mixed-species colonies headed by A. mellifera queens than A. mellifera workers in mixed-species colonies headed by A. cerana queens. Apis mellifera workers in conspecific queenless colonies showed significantly greater ovary activation than those in mixed-species queenless colonies. Quantification of the chemical components of mandibular gland pheromones of queens of the 2 species showed that they are similar. Combined, our results show that queen signals have been preserved between the 2 species and that workers respond to the heterospecific signals from queens. However, despite the similarity in the queen mandibular gland fatty acid secretions between the 2 species, workers respond differentially toward hetero- and conspecific queens. Copyright 2009, Oxford University Press.