Aspects of the interaction between reproductive morphology and social behaviour of a primitively eusocial sweat bee, Halictus ligatus Say (Hymenoptera: Halictidae)

In this thesis, I examine seasonal, behavioural and physiological mechanisms of reproductive conflict between queens and workers of the primitively eusocial sweat bee, Halictus ligatus. I tracked seasonal changes in ovarian condition of both castes to explain variation in reproductive output of bees where varying degrees of sociality characterise colony ontogeny. Based on ovarian development and oocyte size, results suggest reproductive competition between mated workers and queens (unmated workers had undeveloped ovaries throughout the colony cycle). However, mated workers do not lay as many eggs (indicated by reduced number of workers with chorionated eggs and increased frequency of oocyte resorption) as queens suggesting that the latter control oviposition throughout most of the colony cycle.; Laboratory-controlled social interactions using circle tubes were conducted to determine behaviours that rendered queens reproductively dominant over workers. The dominant bee exhibited push, lunge and back without reverse during the first 15–30 minutes of the encounters. In extended encounters, the most remarkable observation made was the switch from mild dominant behaviours to the highly aggressive mandibular hold on the neck. Three workers were killed by their own queen as a result of this escalated aggression.; Extreme aggression of queens toward workers underlies the intensity of reproductive competition between these two castes. Ovaries were examined after queens and workers interacted in circle tubes and after being subjected to simulated aggression. Results from both experiments showed significant reduction of worker ovarian development and increased oocyte resorption compared to controls while that of queens were unaffected. Thus, not only are queens more aggressive but their ovaries are more resilient to the effects of aggression than are those of workers. This suggests that differences in ovarian physiology as well as behaviour are important in determining reproductive fates of individuals in primitively eusocial insects.