Ecdysteroid titer, ovary status, and dominance in adult worker and queen bumble bees (Bombus terrestris)

The role of ecdysteroids in the regulation of dominance and reproduction in social Hymenoptera is little explored. In the current study we compared ec dysteroid titers in hemolymph of individual queen and worker bumble bees (B ombus terrestris) that differ in their behavior, reproductive status and so cial environment. Egg-laying queens that head colonies and have ovaries exh ibiting all stages of follicle development, had a higher ecdysteroid titer than virgin queens whose ovaries contained only follicles at initial stages . In workers, the relationship between ecdysteroid titers and follicle deve lopment appears to be more complex and to be influenced by the bee's social status and social environment. Shortly after emergence, young workers had only follicles at the initial stages of oogenesis and they exhibited a low ecdysteroid titer. No significant, correlation was detected between ovary s tatus and ecdysteroid titer in workers, with some workers showing activated ovaries but low ecdysteroid titers. However, at six days of age, a trend t owards higher ecdysteroid titer was observed for workers in queenless group s, a condition characterized by rapid follicle development relative to quee nright conditions. In these queenless groups, high social status was associ ated with high ecdysteroid titers. By contrast, in queenright workers ecdys teroid titers were low, even for bees with presumably high social status th at had activated ovaries and were observed performing oviposition behavior. This study suggests that ecdysteroids are involved in regulation of reprod uction in B. terrestris. (C) 2000 Elsevier Science Ltd. All rights reserved .