Biogenic amines as mediators of queen mandibular pheromone's control of worker reproduction in the honey bee, Apis mellifera

The occurrence of reproductive and non-reproductive castes is one of the major hallmarks of eusociality. Constraints on worker reproduction negate conflict over queen-worker reproduction, playing an integral role in the maintenance of colony harmony. The primary aim of this thesis was to improve our understanding of one of the major mechanisms maintaining colony cohesion in honey bees: the inhibition of worker reproduction by QMP. A body of circumstantial evidence already implicated biogenic amines as mediators of QMP’s command over the behaviour and ovarian physiology of workers. This thesis aimed to bring further clarity to the roles played by biogenic amines in regulating reproductive constraint, finding evidence that QMP’s ability to modulate dopamine and octopamine is likely a pathway through which sterility in workers is induced.

Considering the accumulation of evidence that QMP ‘chemically castrates’ workers by manipulating fundamental reproductive pathways, the question as to how queens evade the repressive effects of their own pheromone was also addressed. The hypothesis that discrepancies in QMP exposure levels between queens and workers maintains caste-specific differences in QMP’s inhibition of reproduction was empirically tested, and recommendations for further study are suggested.

Finally, the importance of QMP to colony function was considered within the context of an applied issue: pesticide-driven declines of honey bee populations. Despite QMP being central to honey bee biology, its interactive effects with commonly used pesticides has been under-researched. I identify a number of synergistic effects between QMP and the neonicotinoid pesticide imidacloprid on workers which may have negative effects for colony health and productivity. Given the demonstrated breadth of QMP’s effects on the neuroendocrine system, reproductive physiology, and behaviour of workers, a case is made for the inclusion of QMP in future assessments of pesticide lethal and sub-lethal effects on honey bees.