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Theses and Dissertations

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Browsing Theses and Dissertations by Subject "agriculture"

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    ItemOpen Access
    Bee diversity and abundance under a grazed cover cropping management system in eastern Colorado and southwestern Nebraska and evaluating the role of beekeeping education and management on honey bee hive overwintering success in Colorado
    (Colorado State University. Libraries, 2021) O'Brien, Colton, author; Kondratieff, Boris, advisor; Seshadri, Arathi, advisor; Jones, Kurt, committee member
    Bee pollination is essential to the production of many valuable crops in addition to facilitating the reproduction of non-crop flowering plants in the environment. Managed and wild populations of bees face unique and overlapping challenges. Wild bees have been negatively impacted by habitat and forage loss as a result of agricultural intensification. There has been headway in finding solutions that offset the environmental impact of agriculture that benefit wild bees without being a financial burden to the producer. Solutions often include the introduction or retainment of forage and habitat within the agricultural landscape. One example of this is the inclusion of bee-friendly cover crops into a crop rotation. Cover crops can promote agroecosystem services such as, nitrogen fixation, reduce erosion etc., and also provide nesting habitat and forage for pollinators. Chapter one explores bee diversity and abundance under a grazed cover cropping management system in eastern Colorado and southwestern Nebraska. Blue vane traps were used to conduct monthly collections of bees within three cover-cropped fields to evaluate diversity and abundance of bees under varying grazing conditions. There was higher diversity of bee genera in fields where grazing intensity was low but bee abundance was higher in grazed fields with the highest representation being from the ground-nesting genus, Lasioglossum. Setting aside some cover-cropped areas to remain ungrazed, allowing plants to come into bloom will provide nutrition and nesting resources for bees in this region. Pathogens and pests are another set of challenges that pollinators face in the environment. Managed bees can be a source of inoculum for wild bees if hives are not kept healthy. Managed bees often visit the same forage sites as wild bees. These communal areas where wild and managed bees interact present opportunities for pathogens to spill over from the managed populations to the wild populations. Pathogen development and spread within managed populations can often be prevented by good beekeeper practices that keep hives healthy. Chapter two explores the role that beekeeping education plays in honey bee hive health and survival among hobby beekeepers across Colorado. While most commercial pollination services are provided by professional beekeepers with 500 or more hives, the majority of beekeepers in the United States are backyard beekeepers with typical operations of fewer than 50 hives. Despite increased interest in backyard beekeeping, average hive loss in the United States is still 35%-40%. Hive survival depends on beekeeper intervention, but many backyard beekeepers lack training and are unfamiliar with the hive management techniques necessary for maintaining healthy hives. Beekeeping education could help improve overwintering survival among back yard beekeepers. To evaluate the role of education in successful beekeeping, in Summer 2018 and Summer 2019, backyard beekeepers across the state of Colorado were contacted to participate in a honey bee health survey that included a questionnaire and a hive inspection. Using hive management, beekeeper education, mite load, and experience as predictors of hive survival, this study found that hive survival may be positively related to hive management.
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    ItemEmbargo
    The need for new inhibitors of photosynthesis in agricultural settings, and the novel herbicidal compound AS9057
    (Colorado State University. Libraries, 2024) Twitty, Alyssa, author; Dayan, Franck, advisor; Abdel-Ghany, Salah, committee member; Phillip, Yael, committee member
    Due to increased food demand, the need for use of herbicides is both necessary and on the rise. Several herbicide classes target photosynthetic electron transport: HRAC Groups 5, 6, and 22. These herbicides are used in large amounts in many different cropping systems to control several species of broadleaf and grass weeds. The first chapter provides a comprehensive review of what these photosynthesis inhibitors are, how they are used and their mode of action. Presently, commercial herbicides only inhibit electron flow at two different sites (PSII and PSI). Those which inhibit electron flow at PSII block the movement of electrons down the electron transport chain, while those which inhibit at PSI accept electrons. Necrosis developing on the leaves of plants treated with PSII and PSI inhibitors is due to the accumulation of reactive oxygen species. Evolution of resistance, toxicity concerns, and other limitations of these herbicides call for the exploration of new chemistries that can be used to target this pathway. One of these new chemistries has been identified as AS9057. AS9057 is a natural product identified as a novel herbicide with a potentially new mode of action using AI4AI, an AI platform for herbicide discovery developed by Agrematch. Greenhouse trials demonstrated that the herbicidal activity of AS9057 was light-dependent. The rapid burndown symptoms-developing on treated plants, combined with its chemical structure, suggested that AS9057 may target photosystem II. Measurements of photosynthetic electron transport rates in treated plants alongside data from oxygen evolution assays did not support this hypothesis. Further experiments suggested the AS9057 may instead act as an electron diverter. Oxygen consumption assays in isolated thylakoid membranes using a variety of electron transport inhibitors revealed that AS9057 likely acts on photosystem I in a similar manner to paraquat, but at a potentially new step between P700 and NADP+. This is consistent with other reports that AS9057 can act as an electron acceptor for flavoproteins. Ferredoxin-NAPD+ reductase is a flavoprotein with a redox potential similar to that of AS9057. Thus, it is currently hypothesized that AS9057 acts as an electron acceptor at or near the ferredoxin to form a radical and generate reactive oxygen species which causes the light-dependent herbicidal effect which is observed in treated plants from greenhouse trials.