Responses of Queenright and Queenless Workers of Apis Cerana to 9-keto-2(E)-decenoic Acid, a Pheromonal Constituent of the Mandibular Gland

Reproductive parasitism by worker honey bees suppressed by queens through regulation of worker mandibular secretions

Social cohesion in social insect colonies can be achieved through the use of chemical signals whose production is caste-specific and regulated by social contexts. In honey bees, queen mandibular gland pheromones (QMP) maintain reproductive dominance by inhibiting ovary activation and production of queen-like mandibular gland signals in workers. We investigated whether honey bee queens can control reproductively active workers of the intraspecific social parasite Apis mellifera capensis, parasitising A. m. scutellata host colonies. Our results show that the queen’s QMP suppresses ovarian activation and inhibits the production of QMP pheromone signals by the parasitic workers, achieved through differential expression of enzymes involved in the biosynthesis of these pheromones at two points in the biosynthetic pathway. This is the first report showing that honey bee queens can regulate reproduction in intraspecific social parasites and deepens our understanding of the molecular mechanisms involved in the regulation of worker reproduction in social insects.

Pheromones affecting ovary activation and ovariole loss in the Asian honey bee Apis cerana

The Asian hive bee Apis cerana has similar queen mandibular pheromones (QMP) to the Western honey bee Apismellifera. However the effects of individual QMP components have never been tested to determine their effects on the reproductive physiology of A. cerana workers. We fed one queen equivalent of each of the major components of A. cerana QMP to groups of c.a. 500 day-old, caged, workers twice a day until the workers were 10 days old. Half of the cages were also provided with 10% royal jelly in the food. Workers were sampled each day and dissected to determine the number of ovarioles and the degree of ovary activation (egg development). In cages treated with 9-carbon fatty acids ovary activation was minimal, whereas the 10-carbon acids suppressed ovary activation very little. Royal jelly enhanced ovary activation, especially in cages treated with 10-carbon acids. The number of ovarioles declined with bee age, but the rate of decline was slowed by the 9-carbon acids in particular. The results show conservation of the composition and function of QMP between A. cerana and A. mellifera and support the hypothesis that QMP is an honest signal of queen fecundity rather than a chemical castrator of workers.