Reevaluation of the Role of Mandibular Glands in Regulation of Reproduction in Bumblebee Colonies

Possible pheromonal control of worker reproduction was tested in Bombus terrestris. The mode of assay included exposure of callow workers to extracts originating from different queen parts and measuring the effect on the in vitro biosynthesis of juvenile hormone (JH), the apparent gonadotropin in this species. Both queen total body extracts applied to dummies consisting of oven-dried or Soxhlet-washed virgin queen bodies and cuticular washes applied to living virgin queens effectively inhibited the biosynthesis of JH in callow workers. None of the five exocrine glands (mandibular, hypopharyngeal, salivary, Dufour's, and tarsal) demonstrated inhibitory activity. Likewise, the use of synthetic 3-hydroxy acids, found in queen mandibular glands, were ineffective in blocking JH biosynthesis in queenless workers. The results suggest that the queen may use a primer pheromone spread on the epicuticle as a means to inhibit worker reproduction. However, our results are not consistent with the prevailing hypothesis that in B. terrestris the main source of the pheromone that inhibits worker reproduction is in the queen's mandibular glands.