Potential Effects of Biotic and Abiotic Stressors on the Reproductive Health of Honey Bees

Abstract

Apis mellifera Linnaeus honey bees are the most economically important pollinator species in the United States, yet colonies consistently experience high losses as a result of interacting biotic and abiotic stressors. My three-year monitoring effort, performed in collaboration with the Bee Informed Partnership to document and better understand national honey bee colony losses, revealed that high losses continue and vary according to region, season, and year. It also revealed that losses are tightly associated to beekeeping operation size, most likely because of differences in management philosophy concerning the ubiquitous mite Varroa destructor Anderson and Trueman, which deprives parasitized bees from essential nutrients and challenges their immune systems. As an important abiotic stressor, neonicotinoid insecticides can elicit significant negative effects on honey bees; however, the nature of these effects during simultaneous pressure alongside V. destructor is not well known. My experiments suggest that V. destructor and neonicotinoids can act synergistically to reduce worker and drone survival, but not affect other features such as hypopharyngeal gland size in workers and sperm quality in drones. To investigate possible practical mitigation actions by beekeepers against neonicotinoids, I found that artificially increased colony genetic diversity through inter-colony brood mixing had a positive effect on worker survival, but no effect on worker hypopharyngeal gland size Overall, my dissertation provides novel evidence for interactions between two common honey bee stressors, highlights the need for in-depth studies to understand how individual-level effects translate to the colony-level, and demonstrates that honey bee colonies in the United States continue to experience high losses.