Towards defining the molecular mechanism of hygienic behaviour in honey bees (Apis mellifera)

Honey bees (Apis mellifera) are integral components of the agricultural industry, but diseases and parasites like the Varroa destructor mite threaten their health and longevity. Some honey bee colonies harbor natural disease-resistance traits, and proteomics has been a fruitful tool to investigate mechanisms of disease resistance; however, Varroa proteomics is a budding field. One troubling trend is that both honey bee and Varroa proteomics samples consistently result in lower peptide identifications compared to conventional model species, which is hindering research on not only social disease-resistance mechanisms and honey bee-mite interactions, but countless other biological topics. We begin by conducting a proteogenomics interrogation to suggest improvements for both the Varroa and the honey bee genome annotations, and to help alleviate the limitations of proteomics technology. The resulting protein databases and web-based protein atlas will serve as resources for future Varroa and honey bee proteomics experiments. Next, we investigate the chemical ecological aspects underpinning hygienic behaviour in honey bees (one form of social immunity against parasites like Varroa). We use gas chromatography-mass spectrometry to analyze abundances of volatile and non-volatile odorants in freeze-killed and age-matched healthy brood, as well as Varroa-infested and non-infested brood. We identified 10 differentially emitted compounds, 2 of which (β-ocimene and oleic acid) are intriguing candidates as hygienic behaviour-inducers based on their previously known functions in honey bees and other social insects. Next, we investigate these two compounds’ abilities to induce hygienic behaviour using a series of behavioural assays. We found that, depending on the context, both odorants can induce hygienic behavior, and they may be acting synergistically. Finally, we begin to investigate physical and biochemical interactions between these odorants and two odorant binding proteins – OBP16 and OBP18 – which are thought to aid in disease odorant detection. We find that β-ocimene is a ligand of OBP16 and oleic acid is a ligand of both OBPs. We conclude by beginning to develop RNAi and transgenic methods for investigating the roles of these proteins in vivo. Overall, these studies are starting to reveal the simple molecular mechanisms underlying a complex social immunity trait in honey bees.Science, Faculty ofGraduat