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.

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    PESTICIDE RESIDUES IN BEESWAX PREDICT THE OCCURRENCE OF VARROA WITH ALLELES THAT CONFER AMITRAZ RESISTANCE.
    (2024) Hartel, Eric; vanEngelsdorp, Dennis; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Honey bees are important pollinators and are essential to modern industrial agriculture. One of the largest threats to honey bee health is the parasitic varroa mite Varroa destructor. A common method beekeepers use to control varroa is the application of synthetic varroacides. Following years of treatment, varroa have developed resistance to multiple varroacides leading to treatment failures. This project set out to examine the relationship between pesticide residues within beeswax and resistance alleles in varroa. I expected that the presence of varroacides would be positively related to the occurrence of known mutated alleles that confer varroacide resistance to varroa. We looked for 3 different known varroacide resistance alleles, and only found 2, (N87S and Y215H). Both N87s and Y215H confer resistance to amitraz and her metabolite DMPF. Only one mutation, the Y215H mutation, was widespread, occurring in 68% of the 195 mites we examined. We found that the mutation occurred more frequently in mites that were collected from apiaries that had higher DMPF levels. Surprisingly, the presence of other unrelated pesticides (e.g. not having the same mode of action as amitraz) were also positively correlated with the proportion of mutated alleles found. Both the total number of pesticides found in an apiary, and increasing concentrations of fungicides, insecticides, and varroacides (including and excluding DMPF data), predicted higher odds of finding the Y215H mutation. It is unclear if this relationship is a result of a correlation between pesticide levels, if the mutation help benefits the mites resist pesticide more generally, or if the gene has become fixed in the population. It is important to monitor resistance conferring mutations in the varroa mite population in order to help beekeepers make proper varroa management decisions.
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    POLLEN NUTRITION, PESTICIDES, AND PATHOGENS: INTERACTIVE EFFECTS ON HONEY BEE HEALTH
    (2017) Garavito, Andrew; vanEngelsdorp, Dennis; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    While a variety of stressors influence honey bee (Apis mellifera) health, it is the additive and interactive effects of these factors on bee health that have been driving modern research. We devised a set of two experiments to test the effects of multiple stressors on honey bee health. First, we grew sunflowers to test the effects of drought stress and seed treatment on sunflower pollen. We fed the pollen collected from these sunflowers to cohorts of bees that were either infected or uninfected with the microsporidian pathogen Nosema ceranae to find that drought stressed pollen leads to increased mortality in infected bees. Next, we fed 37 experimental pollen diets of different floral varieties and pesticide loads to honey bees infected with N. ceranae, but we were unable to find a connection between diet variety and pesticide exposure on bee health.
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    An analysis of regulatory decisions on food-use pesticides under the Food Quality and Protection Act
    (2012) Newcomb, Elisabeth Jo; Cropper, Maureen L; Agricultural and Resource Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    To ensure the safety of older pesticides used in the United States, the EPA required the reregistration of pesticide uses which were first introduced before 1984. Using a dataset of reregistration outcomes for 2722 pesticide uses applied to food crops, I analyze the extent to which these decisions were determined by chronic health risks, pesticide expenditures, and other factors. I find that the dietary health risks associated with pesticides are had greater influence on actions to reduce dietary and occupational exposures than on pesticide cancellations. High population dietary risks are associated with higher rates of pesticide cancellations, though these results are insignificant. There is evidence that the EPA was more responsive to child and infant dietary risks: values above the EPA's threshold of concern were more than 10% more likely to be cancelled than those that were not (significant at the 10% level). The effects of cancer risks on EPA actions are more ambiguous, though this may be due to data limitations. The less safe pesticides are for handlers, the more often they are cancelled, but pesticide safety has a more significant correlation with reentry intervals. A one percent decrease in the safety of a pesticide to handlers predicts a reduction in reentry interval of 1.6 days (significant at the 5% level). Expenditures on individual pesticides have a strong relationship with pesticide reregistration, with an additional half million dollars in expenditures predicting a 2% increase in the probability of reregistration (significant at the 1% level). Expenditures are not so correlated with reentry intervals or changes in pesticide tolerances. After accounting for dietary risk and pesticide expenditures, Monsanto and Dow were most likely to have uses reregistered. Though there was some concern that small crops with low pesticide expenditures would suffer extra cancellations, small crop uses were no more likely to be cancelled than large crop uses. Mentions of individual pesticides in the media had no apparent relationship with the outcome of reregistration decisions.
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    Ground-dwelling beetles as bioindicators in transgenic corn
    (2009) Lepping, Miles; Shrewsbury, Paula M; Dively, Galen P; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Ecological risk assessment for transgenic crops requires identification of appropriate biological indicator organisms for use in laboratory and field biomonitoring studies. Ground-dwelling predatory beetles in the families Carabidae and Staphylinidae comprise a diverse and abundant group of nontarget organisms in field corn systems where rootworm-resistant transgenic varieties are deployed. First, the utility of two sampling methods (pitfall trapping and suction-based litter extraction) was assessed for estimating ground beetle (Coleoptera: Carabidae) population parameters in Maryland cornfields. Sampling bias was established for pitfall trapping, confirming the limitations of this semi-quantitative method for capturing a representative portion of the epigeal community. Litter extraction data conformed to predictions for abundance in relation to trophic identity, body size and biomass. Litter extraction identified smaller bodied carabid omnivores and carnivores as numerically dominant over larger bodied species that have received focus in risk assessment studies. A small-bodied carabid, Elaphropus xanthopus (Dejean), was identified as the dominant carnivore, and therefore selected for nontarget exposure and toxicity studies. Second, in choice and no-choice experiments, corn pollen was identified as a realistic, direct exposure pathway to transgenic proteins for E. xanthopus. Third, organism-level exposure to Cry34Ab1 rootworm-resistant protein was demonstrated for E. xanthopus in the laboratory and field during corn pollen shed. Field studies also revealed contamination across transgenic and non-transgenic test plots, indicating experimental design must account for the movement of study organisms and/or transgenic plant tissues. Finally, a toxicity study examined the effects of dietary exposure to rootworm-resistant Cry34/35Ab1 corn pollen for two beetle species, a carabid, E. xanthopus, and a staphylinid, Strigota ambigua (Erichson). Transgenic pollen exposure did not affect longevity or sub-lethal behaviors for either species. Small-bodied, predatory ground beetles are recommended as candidate bioindicator organisms in risk assessment studies designed to optimize field monitoring, exposure detection, and bioassay for transgenic pesticides.
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    Contaminants in the atmosphere of the Delmarva Peninsula: impact of local activities and atmospheric transport
    (2007-04-10) Goel, Anubha; Torrents, Alba; McConnell, Laura L; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Anubha Goel, Doctor of Philosophy, 2007 Upper Delmarva Peninsula (within the Chesapeake Bay watershed), where the land use is predominantly agricultural, may be a significant source of pesticides (contributors in the declining water quality and bio-diversity of associated wetlands of the Chesapeake Bay) to the region. Although the Peninsula is predicted to be receiving significant inputs of herbicides through atmospheric deposition, the extent of local or regional atmospheric transport and deposition of pesticides to this area is poorly understood. The goal of this research was to determine the atmospheric levels and estimate deposition flux of pesticides in the Upper Delmarva Peninsula. This was accomplished by collecting weekly air samples (n=271) and event based rain samples (n=489) from three locations in the region (Dover and Lewes, DE; Cambridge, MD) for the period 2000-2003. The samples were analyzed for the presence of 34 pesticides (19 current use (CUPs), 15 historical (HUPs)) and 4 congeners of penta-BDE (PBDEs) using gas chromatograph-mass spectrometry (GC-MS). Statistically analyzed data was used to evaluate factors impacting phase distribution and the contribution of wet deposition to the levels in Chesapeake Bay. The more persistent insecticides and fungicides occur ubiquitously while application on corn influences herbicide occurrence and levels. Atmospheric CUP levels are driven by regional agricultural activity. CUPs do not exist in equilibrium and local meteorological conditions (like high relative humidity) influence phase distribution. The wet deposition flux of insecticide and fungicide is dependent on the total rainfall amount during the sampling period while timing and frequency relative to application on corn impacts herbicide flux. Levels in rainwater of some pesticides (endosulfans, chlorothalonil, diazinon etc.) were high enough to be of concern for the biota associated with the region's water bodies and associated wetlands and reveals that atmospheric deposition arising out of short range atmospheric transport can result in significant pesticide input to non-target areas. HUP atmospheric levels are lower than in the Great Lakes and are decreasing at a faster rate. This study reveals that spray irrigation of treated wastewater is an unknown source of toxic PBDEs to the atmosphere and can result in elevated levels at locations downwind of the irrigation field