Regulation of worker activity in the primitively eusocial wasp Ropalidia cyathiformis

Abstract

Ropalidia marginata, traditionally regarded as a primitively eusocial wasp species appears to have acquired some features reminiscent of highly eusocial species. Queens are behaviorally passive individuals, yet maintain complete reproductive monopoly and probably use pheromones to achieve this. Regulation of worker foraging is achieved by the workers themselves in a decentralized, self-organized manner. If there are other species in the genus Ropalidia that do not show such relatively 'advanced' features, this genus can provide an attractive model system to investigate the evolutionary transition from the primitively eusocial to the highly eusocial state. Here, we therefore investigate the congeneric Ropalidia cyathiformis and demonstrate that in contrast to R. marginata, it appears to be a typical primitively eusocial species. As expected therefore, and in striking contrast with R. marginata, R. cyathiformis queens are the most, or among the most, dominant, active and interactive individuals and their behavior is consistent with the possibility that they suppress worker reproduction and regulate worker foraging in a relatively centralized manner. Upon removal of the queen, a potential queen with levels of aggression even higher than that of the queen, becomes apparent immediately. Such a potential queen appears to take over inhibition of worker reproduction and regulation of worker foraging by mechanisms similar to that used by the queen so that, there is no disruption in foraging and brood care. We suggest that comparative studies of R. marginata and R. cyathiformis provide a unique opportunity to investigate the evolutionary transition from the primitively eusocial to the highly eusocial state.