Graduate Thesis Or Dissertation

 

Colony Level Infection of Honey Bee Gut Pathogen, Nosema ceranae and Role of Pollen Nutrition in Nosema ceranae Infection and Bee Survival Public Deposited

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  • Honey bees are important pollinators for many agricultural systems throughout the world. However, recent honey bee declines have caused great alarm, drawing attention to the vulnerability of worldwide agriculture to pollinator loss. These declines are often attributed to a combination of pests, pathogens, viruses, chemicals, and a lack of proper nutrition. One of the main factors implicated in bee declines is the fungal pathogen Nosema ceranae. There has been significant research conducted to understand the effect of Nosema ceranae infection in individual bees, but currently there is a gap in knowledge regarding Nosema ceranae infection at the colony level. Also, little is known regarding the effects of bee nutrition on Nosema ceranae infection and longevity of infected bees. Here I investigated the dynamics of colony level infection of Nosema ceranae and determined the effects of pollen nutrition on Nosema ceranae infection and survival of bees. To understand the dynamics of Nosema ceranae infection at the colony level, I examined the prevalence (proportion of infected bees) and intensity (number of spores per bee) in two different field experiments with whole colonies. In the first experiment, I compared Nosema infection information from bees of known ages to the traditional method of colony infection diagnosis. In the second experiment, I analyzed each individual bee from eight experimental nucleus colonies inoculated with Nosema ceranae to determine the infection prevalence and intensity. I found that the prevalence and intensity of Nosema ceranae infection was significantly influenced by honey bee age. Both experiments showed that foraging-aged bees had a higher prevalence of Nosema infection than younger bees. However, I found that nurse bees may have spore intensities comparable to or greater than those of forager bees. These results emphasize the limitations of the traditional Nosema sampling methods in assessing the colony infection status. My findings are expected to assist in development of reliable Nosema sampling protocols that could help beekeepers realistically assess the need for colony treatment. Nutrition has a profound effect on host-parasite relationships; hence it is imperitive to understand how honey bee nutrition affects Nosema ceranae prevalence and intensity. In this study, I examined effects of different concentrations of pollen on the prevalence and intensity of Nosema ceranae as well as the longevity and nutritional physiology of infected bees. Significantly higher spore intensities were observed in treatments that received higher pollen concentrations when compared to treatments that received relatively lower pollen concentrations. Interestingly, the bees in higher pollen concentration treatments also had significantly higher survival despite higher intensities of Nosema ceranae. I found that hypopharyngeal gland protein content was significantly different between bees infected with Nosema ceranae and bees that were not infected, but did not find any significant differences in total midgut enzyme activity between infected and non-infected bees. My results demonstrate that optimal pollen nutrition increases Nosema ceranae intensity, but also enhances the survival or longevity of honey bees. The information from this study could be potentially used by beekeepers to formulate appropriate protein feeding regimens for their colonies to mitigate Nosema ceranae problems.
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