Hormonal and Pheromonal Regulation of Reproduction in the Bumble Bee Bombus terrestris

Abstract

Bombus terrestris constitute important pollinators of greenhouse crops. In Israel the species utilized is, whose colonies are reared commercially. This is a primitively social species with a particular colony development. It encompasses two social phases: a eusocial phase in which the queen dominates reproduction, and a competition phase in which workers compete with the queen for the parentage of males. These workers are distinguished by accelerated ovarian development, high production of JH, and elevated levels of dopamine in the brain. Queen-worker conflict is also manifested in overt aggression among all members of the nest. High aggression is correlated with dominance status of the bees and is also correlated with octopamine levels in the brain. After verifying that JH III is the only JH produced by the bees and validating the assay for its measurements (RCA & RIA), we used JH as an indicator of worker reproduction. Queens taken from colonies both before and after the competition phase were equally effective in inhibiting worker reproduction. Moreover, there is only a narrow window, around the competition point, in which workers may have the opportunity to initiate reproduction. Before that point they are inhibited by the dominant queen, while after that point both the queen and those workers with accelerated ovarian development exert strong inhibition on worker nest mates. Thus, "queen dominance deterioration" is not the primary cause in eliciting the queen-worker conflict. Queens convey their presence by means of a chemical signal that is extractable in organic solvent and that is normally spread on the cuticle. Total body extract and body washes, applied on dead virgin queens, were able to inhibit the release of JHin vitro in queenless workers. However, none of the prominent exocrine gland investigated mimicked this function. It is possible that the source of the putative pheromone is an unknown gland, or that it emanates from an assembly of glands. Chemical analyses of the prominent glands revealed a plethora of compounds the function of which should be further investigated. Understanding the social behavior of B. terrestris paves the way to facilitate colony manipulation and to adjust the colonies for specific pollination requirements.