Queen Mandibular Pheromone Prevents, but Does Not Reverse, Worker Reproduction in Apis Mellifera, Unlike in Drosophila Melanogaster.

The reproductive division of labour is the defining feature of eusociality, in which reproduction is monopolised by one, or a small subset, of individuals within a colony. In the Western Honeybee Apis mellifera, workers are reproductively constrained by a suite of mechanisms, but primarily by queen mandibular pheromone (QMP). The adult developmental limits of QMP's ability to repress worker reproduction and its ability to suppress reproduction once ovaries have begun to activate remain unresolved. Here, we investigated the limits of plasticity of QMP mediated reproductive repression and compared it to Drosophila melanogaster. By manipulating the timing of QMP exposure and withdrawal in caged honeybee workers, we show that QMP inhibits ovary activation across early adult development, even when exposure is delayed for several days post-eclosion, and that this inhibition is reversible upon removal of QMP. We also show that QMP alone is unable to bring about repression of honeybee worker ovaries once they have activated, indicating that there is an intrinsic limit to QMP-mediated reproductive plasticity in honeybee workers. This contrasts with D. melanogaster where QMP exposure significantly reduced oogenesis even in active ovaries. These findings indicate that there are species differences in reproductive plasticity; and that in honeybees, QMP acts primarily as an inhibitor of adult reproductive development rather than as a reversible regulator of adult reproduction, with reproductive repression likely requiring other additional colony cues.