Hormonal Regulation of Behavioral and Phenotypic Plasticity in Bumblebees

Bumblebee colonies transition through several social phases during their life cycle (encompassing a solitary phase, a cooperative phase, and a final phase of overt conflict), thus providing an excellent model for examining the mechanisms underpinning social behavior. Furthermore, as key pollinators of several agriculturally important crops, understanding how their social behavior and life cycles are regulated is essential to effectively manage and conserve bumblebees. Here we discuss the role of key hormones and pheromones in shaping queen and worker physiology and behavior, as mediators of both social cooperation and social conflict. Juvenile hormone, in conjunction with ecdysteroids, plays a central role in caste determination during larval development. In the adult bee, juvenile hormone acts as a gonadotropin, while brain biogenic amines and vitellogenin are involved in dominance hierarchy establishment. The pheromonal output of Dufour's gland is involved in signaling both sterility and worker task. The labial gland secretion is also caste specific, and the observed changes in the composition of the queen's secretion may signal the switch from production of sterile workers to production of future queens (gynes), and hence the eruption of queen-worker competition over reproduction. The recent sequencing of two bumblebee genomes provides the opportunity to greatly advance our understanding of the hormonal and pheromonal mechanisms underlying social evolution.