Graduate Thesis Or Dissertation
 

Improving Honey Bee Health: Evaluating Efficacy and Safety of Oxalic Acid Vaporization Tactic for Varroa destructor Control and Understanding Factors Triggering European Foulbrood Disease

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cv43p510n

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  • Honey bees are vital for our food production and ecosystem due to their critical pollination services. The beekeepers in the United States and worldwide have reported significant colony losses for over fifteen years. Several stressors are implicated in these colony declines, including parasites, diseases, poor nutrition, and pesticide exposure. There is abundant research geared towards understanding the factors impacting honey bee health and formulating best management practices. However, there still needs to be more knowledge on these stressors and management practices. This thesis attempts to fill gaps in knowledge about a critical Varroa control option and the incidence of European foulbrood (EFB) disease in Oregon by (1) evaluating the efficacy and safety of oxalic acid vaporization method to control Varroa destructor and (2) understanding factors contributing to EFB in honey bee colonies pollinating blueberries. Varroa destructor, known as Varroa mite, represents a significant threat to honey bee colonies worldwide. This leads to bee population declines and risks to global agricultural crop yield due to inadequate pollination. Varroa is an external parasite infesting both adult bees and developing broods, inducing physiological stress, transmitting harmful viruses, and ultimately jeopardising the survival of bee colonies. The ability of this mite to reproduce within capped brood cells and its rapid spread within colonies exacerbate the severity of infestations. The beekeepers have limited options to mitigate Varroa infestation. Oxalic acid vaporization is a relatively new option for beekeepers to control Varroa mites. Hence, there still needs to be more knowledge regarding the efficacy and safety of this method/product. In Chapter 3, I delineate a two-year field experiment where I evaluated the effects of different doses of oxalic acid on Varroa and honey bee larval development. The oxalic acid vapor was applied weekly for three weeks. In 2021, oxalic acid was administered as vapor in doses of 1g, 2g, and 4g, whereas in 2022, the doses were limited to 3g and 4g. Additionally, in 2022, we assessed the impact of oxalic acid vapor on larval mortality. At the same time, lower doses (1g and 2g) of oxalic acid showed no significant difference in Varroa levels from the control group. However, the 4g dose significantly decreased Varroa numbers and adversely affected honey bee larval development. The 3g dose of oxalic acid vapor appeared to be an optimal treatment, showing effectiveness in Varroa control without significant negative impacts on honey bee larval mortality. With careful dosage considerations, oxalic acid is an environmentally conscious control measure for Varroa mite infestations, contributing to the global resilience and sustainability of honey bee colonies. European foulbrood (EFB) is a detrimental honey bee brood disease that causes a considerable economic impact on the beekeeping industry. Despite being a relatively well-explored disease, the factors influencing its incidence and spread need to be better understood. Notably, for the past few years, commercial beekeepers in the Pacific Northwest, particularly in Oregon and Washington, have reported increased occurrences of EFB in colonies engaged in blueberry pollination. In Chapter 4, I describe an observational study examining potential factors contributing to the higher incidence of EFB in honey bee colonies employed for blueberry pollination by measuring several relevant parameters. In this study, we collaborated with five Oregon-based beekeepers. We used 152 honey bee colonies placed in blueberry and non-blueberry fields: the non-blueberry fields comprised meadowfoam, canola, turnip, and a holding yard. Our investigation spanned two sampling periods. In all experimental colonies, we assessed bee populations, and documented EFB-infected larvae. We analyzed the head protein and abdominal lipid content of nurse bees collected from colonies at the beginning and termination of the study. We also collected pollen by installing pollen traps on four colonies in each field to estimate the amount and diversity of incoming pollen. While slightly higher EFB incidence was observed in colonies engaged in blueberry pollination compared to other crops or holding yards, we did not observe any significant differences in other measured parameters. We could not find any correlations between the measured parameters and EFB incidence. Our findings indicate that EFB is a complex disease, and it is difficult to tease apart factors contributing to its incidence in honey bee colonies. A more comprehensive and large-scale longitudinal study is needed to resolve the factors that cause EFB outbreaks.
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