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Author ORCID Identifier


Campus-Only Access for Five (5) Years

Document Type


Degree Name

Doctor of Philosophy (PhD)

Degree Program

Organismic and Evolutionary Biology

Year Degree Awarded


Month Degree Awarded


First Advisor

Lynn S. Adler

Subject Categories

Ecology and Evolutionary Biology | Entomology | Environmental Microbiology and Microbial Ecology | Nutrition | Parasitology


Bees are critical pollinators, but some populations are in decline due to a variety of interacting stressors, such as pathogens and reduced floral diversity. In Chapter 1, we summarize current knowledge on bee pathogen defense mechanisms. This review highlights knowledge gaps in the field, such as the role of diet in disease resistance. Sunflower pollen reduces the gut pathogen Crithidia bombi in commercially reared bumble bees (Bombus impatiens). Commercial bumble bees have become popular research models, but few studies test whether results translate to other pollinators. In Chapter 2, we assessed the effect of sunflower pollen on infection in wild B. impatiens and three wild congeners. We also asked how pollen diet and infection affected performance in wild B. impatiens microcolonies. Compared to controls, sunflower pollen reduced Crithidia infection in commercial and wild B. impatiens, had weaker effects in B. bimaculatus and B. vagans, and had no effect in B. griseocollis. In microcolonies, 50% sunflower pollen reduced infections, but also reproduction, compared to wildflower pollen. This suggests that sunflower pollen could control Crithidia infections in B. impatiens and potentially close relatives, but may hinder reproduction if other resources are scarce. In Chapter 3, we tested whether sunflower’s medicinal effect is due to changes in bee immunity. We found that sunflower pollen did not significantly affect hemolymph phenoloxidase or antibacterial activity, suggesting other mechanisms are responsible. In Chapter 4, we investigated the effect of pollen diet diversity on the health of Bombus impatiens and the solitary alfalfa leafcutter bee, Megachile rotundata. We fed bees one-, two-, or three-species pollen diets and assessed gut bacterial communities (via 16s rRNA sequencing) in both species, and immunity (via melanization) in B. impatiens. Pollen diets included dandelion, staghorn sumac, and hawthorn alone, each pair-wise combination, or a mix of all three species. In B. impatiens, pollen diet composition, but not diversity, affected communities in older workers, but had no effect in newly emerged bees. Pollen diet diversity did not affect immunity in B. impatiens or the gut microbiome in M. rotundata. This dissertation improves our understanding of the effects of landscape simplification and pathogens on wild bee health.