Impacts of inter-colony distance, mite host choice, and colony polyandry on the host/parasite relationship between Apis melliferaand Varroa destructor
Nolan, Maxcy Pearle
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The parasitic mite Varroa destructor Anderson and Trueman has become the single greatest threat to the honey bee (Apis mellifera) since its shift from its native host Apis cerana. This dissertation explores the impacts of inter-colony distance, mite host choice, and colony polyandry on the host/parasite relationship between these two organisms. Findings here showed that inter-colony distance affects Varroa mite counts within honey bee colonies, in that apiaries in which colonies were spaced 100 m apart contained lower mite population averages than 0 m or 10 m spacings. These findings suggest that mite populations are resource-regulated at a landscape scale. The link between reproductive value and risk assessment was examined in pre- and post-partum mites. Given that theory assigns greater reproductive value (predicted future offspring) to younger individuals, I hypothesized that a mite’s reproductive value affects its propensity to disperse. In the study, both pre- and post-partum mites preferred newly emerged workers over pollen foragers; however, a bias for newly emerged bees was earlier and more strongly sustained among pre-partum mites. This suggests comparatively greater dispersal risk tolerance among post-partum mites. The condition of polyandry, or multiple matings, among honey bees increases intra-colony genetic diversity and may play a role in nestmate discrimination. Additionally, recent evidence suggests a positive relationship between genetic variance and colony fitness. My results found no significant difference in drift or heterocolonial worker acceptance between colony classes of 5- and 15-drone inseminated queens, which are within natural mating numbers. Based on the results, nestmate recognition is not affected by intra-colony genetic variance encompassing natural levels. Furthermore, I measured metrics of colony strength, parasite resistance, comb building, and forager recruitment as evidence of the benefits of genetic variance to colony fitness. No significant differences were detected in any of the categories except in forager recruitment, which found an increase in forager recruitment in colonies with lower genetic diversity. These results suggest variation in colony genetic diversity encompassing natural mating numbers does not affect colony fitness.