Regulation of reproduction by dominant workers in bumblebee (Bombus terrestris) queenright colonies

The mechanisms of regulating worker reproduction in bumblebees were studied by direct behavioral observations and by measuring ovarian development and juvenile hormone (JH) biosynthesis rates in workers under different social conditions. Workers in the last stage of Bombus terrestris is colony devel opment (the competition phase) had the lowest ovarian development and JH bi osynthesis rates. Gallows introduced into colonies immediately after queen removal (dequeened colonies) demonstrated a significant increase in ovarian development before, bur not during, the competition phase. These findings differ from the higher ovarian development in colonies during the competiti on phase predicted by the prevailing hypothesis that worker reproduction st arts in response to a decrease in queen inhibition. Reproduction of callows housed with dominant workers in small queenless groups was inhibited as in queenright colonies. This suggests that the reduced ovarian development an d JH biosynthesis rates observed in dequeened and normally developing colon ies during the competition phase also reflect inhibition by dominant worker s. Thus, two distinct stages of inhibition of reproduction seem to exist: ( 1) before the competition phase, when the queen slows down worker ovarian d evelopment and prevents oviposition; (2) during the competition phase, when dominant workers inhibit ovarian development of other workers. Between the se stages there seems to be a temporal "window" of enhanced worker reproduc tive development. The queen's typical switch to haploid egg production was not associated with changes in worker ovarian development or JH biosynthesi s rates. These findings suggest that regulation of worker reproduction in B . terrestris is not determined by simple changes in the queen's inhibition capacity or by the sex of offspring and that the worker's role is more impo rtant than previously believed.