Over the last several decades declines in pollinator populations, especially those of wild bees and other insects, have raised awareness of the economic impact pollination services have for crop production. This awareness and concern was heightened by an ongoing loss of millions of managed honey bee colonies since the early 1950s. Colonies are used predominantly for pollination services in fruit and vegetable crops. During 2007, an unusually large overwintering loss in colonies that was not characterized by the presence of dead bees was termed colony collapse disorder (CCD), a syndrome in which hives lacked sufficient worker caste bees to maintain the queen and brood. Potential factors hypothesized to be associated with CCD include parasite infestations (e.g., Varroa mite) and pathogen infections (Nosema spp. fungus and viruses), insecticide exposure (especially to the neonicotinoid class), and poor nutrition owing to a reduction in landscape areas containing high quality floral resources. Although no one stressor has been definitively associated with CCD, possible interactions among them have only recently been studied. Of particular interest are possible interactions of Nosema spp. with neonicotinoid insecticide exposure. The main objective of this dissertation was an examination of these potential interactions using a combination of literature analysis, empirical study of Nosema infection prevalence in adult bees, and simulation modeling of the combined effects of several stressors on worker population abundance. After the introduction, the dissertation is divided into four chapters addressing the following objectives: (1) Comparison of regulatory procedures for risk assessment of insecticides potentially impacting honey bees in the United States and in the European Union; (2) Analysis of published literature that document potential interactions between bee pathogens, parasites, and neonicotinoid insecticide residues; (3) Analysis of field-collected apiary bees for prevalence of Nosema spores in association with land uses and the presence of neonicotinoid residues; (4) Use of the honey bee colony model BEEHAVE to predict colony collapse in the presence of pathogens and insecticide-induced mortality. Results of the various analyses suggest a need for modifying risk assessment procedures to include the interaction of pesticide residues with parasite/pathogen stressors.
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