Date of Graduation

8-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Entomology (PhD)

Degree Level

Graduate

Department

Entomology and Plant Pathology

Advisor/Mentor

Joshi, Neelendra K.

Committee Member

Adamczyk, John J.

Second Committee Member

Szalanski, Allen L.

Third Committee Member

Rojas, Alejandro

Keywords

Bee health; Bee toxicology; Mason bees; Osmia

Abstract

Several mason bees (Osmia spp.), such as Osmia lignaria and Osmia cornifrons, are efficient and valuable pollinators in orchards. They can be used to supplement honey bee (Apis mellifera) pollination, to improve yields and reduce costs compared to A. mellifera alone. Osmia spp. encounter many stressors in their environment, which can negatively impact their health and pollination ability. These stressors include pesticide use and habitat loss due to agricultural expansion. Apis mellifera are often used as surrogates for pesticide risk assessment, but different bee species can vary widely in their response to stressors. Therefore, research into the impact of stressors on solitary bees is needed to create mitigation strategies and better protect the health of bee communities. This study assessed the lethal and sublethal impacts of pesticides on Osmia spp. health, physiology, and ability, and the effects of floral diversity on bee activity and fecundity. As pest insects become more resistant to commonly applied pesticides, new active ingredients and formulations are produced to provide effective pest control. Two recently released systemic insecticides, flupyradifurone and sulfoxaflor, can be used to combat neonicotinoid-resistant pests, but may pose a risk to Osmia spp. We exposed four bee species, A. mellifera, O. lignaria, O. cornifrons, and Osmia californica, to both insecticides and measured toxicity, as LD50 values, and survival over 96 hours. Apis mellifera was the least sensitive to both insecticides, followed by O. cornifrons. Osmia lignaria and O. californica were the most sensitive. Female Osmia bees were more sensitive than males of the same species. The sublethal impacts of flupyradifurone and sulfoxaflor on Osmia spp. health were measured, using their detoxification enzyme expression, feeding preferences, flight and foraging ability, and gut microbial communities after exposure. Additionally, O. cornifrons were exposed to the commonly used garden pesticides, glyphosate, chlorothalonil, and spinosad, and their gut bacterial communities were compared. Flupyradifurone, but not sulfoxaflor, increased the expression of P450 enzymes in O. lignaria females. Flupyradifurone also caused impaired mobility and foraging activity of O. lignaria females at 24 hours following exposure. Osmia lignaria females showed some avoidance of food contaminated with higher concentrations of flupyradifurone, but overall O. lignaria did not avoid sulfoxaflor or flupyradifurone. The effects of the tested pesticides on O. cornifrons gut bacterial community composition and diversity were minimal. Finally, we raised O. lignaria in field cages planted with either a wildflower mix or a buckwheat monoculture and measured the effects on bee activity, fecundity, and soil health. The different planting types had little impact on soil nutrient content and the soil microbiome. Osmia lignaria, however, were more active and were successfully able to reproduce in the wildflower mix groups, whereas bees in the buckwheat groups had lower activity and produced no offspring. This work demonstrates the risk of insecticides to Osmia spp. health and pollination ability and the importance of an adequate and varied diet for bee fecundity.

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