To determine whether ecdysteroids are associated with reproductive division of labor in Bombus terrestris, we measured their levels in hemolymph and ovaries of queens and workers. Queens heading colonies had large active ovaries with high ecdysteroid content, whereas virgin gynes and mated queens before and after diapause had undeveloped ovaries with low ecdysteroid content. The hemolymph ecdysteroid titer was rather variable, but in a pooled analysis of mated queens before and after diapause versus colony-heading queens, ecdysteroid titers were higher in the latter group. In workers, agonistic behavior, ovarian activity, ovarian ecdysteroid content, and hemolymph ecdysteroid titers were positively correlated, and were lowest when a queen was present. In queenless workers, ecdysteroid levels were elevated in dominant workers, and were also influenced by the presence of brood and by group demography; hormone levels were higher in bees kept in larger groups. These findings are consistent with the premise that in B. terrestris the ovary is the primary site of ecdysteroid synthesis, and they show that ecdysteroids levels vary with the social environment.
Bibliographical noteFunding Information:
We thank Ada Eban for help with observations, Ram Tamir, Avital Dov, Ada Eban, and Hadas Sarid, for help with the bees, Mira Cohen for general technical assistance in the lab, Polyam Pollination Services, Yad-Mordechai for technical help and hospitality, and two anonymous reviewers for helpful comments on a previous version of this manuscript. Financial support was provided by the Israel Science Foundation (ISF, Grant no. 606/02, to GB), and the US–Israel Bi-national Science Foundation (BSF, Grant no. 2001-022-2, to GB).
- Bumble bees