UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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2018 - 20192

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    Effect Of Nrf2 Inducers On Honey Bee Gene Expression And Pesticide-Related Mortality
    (2019) Brandt, Elizabeth A.; Hawthorne, David; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Honey bees are vitally important as pollinators to ecosystems and agricultural economy, yet they are threatened by the presence of pesticides and the wide array of xenobiotics they encounter while foraging. To better understand their metabolic detoxification of these compounds, it is important to elucidate the gene expression pathways involved in their response to toxin exposure. I investigated the potential detoxification role in honey bees of the Nrf2/Keap1 regulatory pathway, one of the most well-researched cellular toxin response mechanisms in vertebrates. I analyzed the effect of inducers on the toxicity of three different pesticides when exposed to bees, and the effects of Sulforaphane on select detoxification gene expression. Inducer consumption effects on pesticide toxicity ranged from synergistic to abrogative depending on the pesticide tested. PCR analysis of gene expression did not reveal significant effects of inducer consumption on expression of detoxification genes. This study and its results lay important groundwork for future research of this regulatory pathway in honey bees.
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    NOVEL ADAPTATIONS IN MORPHOLOGY, DEVELOPMENT, AND NUTRIENT AQUISITION FOR HOST EXPLOITATION IN THE MESOSTIGMATID HONEY BEE PARASITE VARROA DESTRUCTOR
    (2018) Ramsey, Samuel David; vanEngelsdorp, Dennis; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The parasitic mite Varroa destructor is the most significant single driver of the global honey bee health decline. Better understanding of the association of this parasite and its host is critical to developing sustainable management practices. This work shows that Varroa is not consuming hemolymph as has been the accepted view, but damages host bees by consuming fat body. Feeding wounds in adult bees were imaged for the first time showing that Varroa feed on the underside of the abdomen where fat body is the immediate underlying tissue. Fat body at the wound site showed evidence of external digestion. Hemolymph and fat body in honey bees were then marked with fluorescent biostains. Fluorescence associated with the fat body was consistently detected in the gut of mites fed on these bees while comparatively little fluorescence was detected from the hemolymph biostain. Mites were then fed a diet composed of one or both tissues. Mites fed fat body tissue survived longer and produced more eggs than those fed hemolymph. Mites fed hemolymph showed fitness metrics no different from the starved control group. Collectively, these findings show that Varroa are exploiting the fat body as their primary source of sustenance; a tissue integral to proper immune function, pesticide detoxification, overwinter survival and several other essential processes in healthy adult and immature bees. Additional study was undertaken to better understand how the Varroa accelerates its reproductive rate. Via gel electrophoresis and immunodetection, undigested honey bee vitellogenin was found in Varroa eggs. The presence and identity of these host proteins was confirmed via HPLC MS/MS. This particular cleavage of vitellogenin is found only in the fat body. These findings fundamentally alter our understanding of the etiology of varroosis and underscore a need to revisit our understanding of this parasite and its impacts, both direct and indirect, on honey bee health. Further study of Varroa adaptations focused on expanding knowledge of Varroa morphology with the aim of determining features that can distinguish between Varroa species. Using low temperature scanning electron microscopy, we were able to provide better resolution of key morphological features, detail variability within traits, and provide novel descriptions of certain characters.