Browsing by Subject "bees"
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Item Evaluating Landscape and Local Drivers of Pollination in Melittophilous Tallgrass Prairie Forbs: Effects of Surrounding Land-use on Pollen Limitation of Chamaecrista fasciculata & Prescribed Burning on Flowering and Pollination of Dalea purpurea(2020-01) Ritchie, AlanTallgrass prairies are one of the most endangered ecosystems in North America. Habitat loss and degradation of remaining prairies threaten both the biodiversity and functioning of these ecosystems. At the landscape scale, loss and fragmentation of existing prairie may limit regional pools of species and abundance of individuals, hampering movement of plants and animals between suitable habitats. At the local scale, degradation of prairies has been exacerbated by loss of native grazers and suppression of fire, the major ecological forces that historically shaped prairie species and communities. While the impacts of these factors on biodiversity in prairies is well-established, little is known about the role of these factors on plant-pollinator interactions, an important ecological process for many prairie forbs. As restoration of prairie habitats is one of the chief means of protecting prairie habitats and biodiversity, evaluating the roles of these factors in mediating ecological processes such as pollination will be critical to their reconstruction. Within this thesis, I explore how two important aspects of habitat restoration management, landscape context and prescribed burning, influence pollination in two common, widespread prairie forbs reliant on insects, namely bees, for pollination. The findings of these studies serve as initial assessments of two under-explored topics with relevance to tallgrass prairie conservation: how placement of a restoration effects recruitment of pollinators and the pollination they provision a habitat, and how animal-mediated pollination influences prescribed burning’s effects on plant reproduction.Item Integrating science and policy: examining effects of neonicotinoid insecticides on honey bee (Apis mellifera L.) and bumble bee (Bombus impatiens Cresson) queens, worker bees, and colony development(2015-09) Wu-Smart, JudyExposure to neonicotinoid insecticides has been highly debated as a major contributor to the decline of bee health. In response to concerns over the potential effects of neonicotinoids on bees, the United States Environmental Protection Agency (US EPA) has made improvements to the regulatory risk assessments process for systemic insecticides. These improvements refine toxicity testing procedures to better establish appropriate uses (acceptable targets) and inform labeling (application rates and timing) to minimize non-target, or unintended, effects on bees. The main objective of these improvements is to increase field realism to obtain more accurate assessments on risks to bees in a natural setting. Each of the following chapters of this dissertation addresses a different aspect of the new risk assessment approach and provides data or suggestions to improve the procedure to better assess non-target effects of systemic neonicotinoid insecticides on bee pollinators. In the first chapter, experiments are described whereby honey bees (Apis mellifera L.) and bumble bees (Bombus impatiens Cresson) were fed imidacloprid syrup in acute toxicity tests at different concentrations, either at the standard quantity (10µl) or at a more field-realistic quantity (50µl) that resembled the amount of nectar foraging bees may hold in their crop to bring back to the hive, or nectar carrying capacity. Results indicated that bumble bees were more sensitive to imidacloprid than honey bees. Bumble bees were particularly more susceptible to becoming unresponsive after exposure rendering them nonfunctional and thus “ecologically dead.” In addition, the “lethal” concentration was considerably lower when measured endpoints included bees that were either physiologically dead or ecologically dead, suggesting higher toxicity to bees when toxicological consequences were considered in an ecological context. In chapter two, honey bee (A. mellifera) colonies consisting of various worker-population sizes (1500, 3000, and 7000 bees) were exposed chronically to imidacloprid syrup (0, 10, 20, 50, and 100ppb) for three weeks to assess the potential effects on queen bee fecundity and colony development. My results are the first to show dose-dependent effects of imidacloprid exposure on queen egg laying and locomotor activity, as well as on worker bee behavior, brood production, and pollen stores in all treated colonies. In addition, such negative effects lessened as colony size increased, suggesting that population size may act as a buffer to pesticide exposure through foraging efforts and increased nestmate interactions that might dilute exposure levels. In chapter three, I fed individual bumble bee (B. impatiens) queens imidacloprid chronically for 18-days. Imidacloprid was administered in syrup (1, 5, 10, 25 ppb) and pollen (0.3, 1.7, 3.3, 8.3ppb) in cage studies. Bumble bee queens exhibited reduced survival at all doses, even as low as 1 ppb. All treated queens that survived their initial exposure exhibited a significant dose-dependent delay in nest initiation or egg-laying, which led to the delayed emergence of worker brood. However, treated queens eventually commenced nest initiation after exposure, suggesting some recovery potential. The final chapter reviews the existing literature on effects of neonicotinoids on bees and organizes the findings using the Adverse Outcome Pathway approach to create a conceptual framework from which to better understand causal linkages among adverse effects across studies. In doing so I created a mechanistic explanation or pathway relating the mode of action of neonicotinoids to the specified adverse outcome: inhibition of colony development in honey bees and bumble bees by neonicotinoid exposure.Item Pollination of a bee dependent forb in restored prairie: No evidence of pollen limitation in landscapes dominated by row crop agriculture(2020-03-02) Ritchie, Alan D; Lane, Ian G; Cariveau, Daniel P; ritch173@umn.edu; Ritchie, Alan; University of Minnesota Bee LabThis data set was generated by an experiment wherein we examined how the amount of agriculture surrounding restored tallgrass prairies affects pollination within restorations by deploying sentinel arrays of a native bee-pollinated forb to 8 sites occurring along an agricultural land-use gradient in western Minnesota, USA. We conducted a pollen limitation experiment on our arrays to measure the effect of the landscape surrounding a restoration on pollination, hypothesizing that sites surrounded by more corn and soy, the dominant driver of habitat loss and fragmentation in this system, would experience decreased pollination. We also hand net bees at these sites to test whether agriculture limits bee abundance in these restorations. Very few studies examine both pollen limitation and pollinator abundance in restorations at a landscape scale. Our data set consists of seed set data for individual plants used in our arrays, restoration site information and the proportion agriculture surrounding each restoration, and bee abundance data for each site.