Functional immune responses of bumble bees in response to parasitism and medicinal diet

Host diet can play a key role in shaping dynamics between pollinators and pathogens. Crithidia bombi is a prevalent trypanosomatid gut parasite that reduces bumble bee survival and reproduction. Sunflower pollen reduces gut infections of C. bombi in Bombus impatiens, the common eastern bumble bee, by approximately 80%. The mechanism(s) underlying this effect are not fully understood, but prior studies have ruled out effects of metabolites, fatty acids and diuretics. Instead, sunflower pollen’s echinate morphology may play a role in reducing infection. Bees consuming sunflower pollen have upregulated immune transcripts associated with detoxification and gut epithelial repair, suggesting direct interactions between sunflower pollen and the gut lining of bees. Sunflower pollen may abrade the gut lining, upregulating immune responses such as epithelial turnover and mucus production, thus altering parasite attachment and fecal composition. To test if sunflower pollen consumption alters feces, we compared evaporation times of fecal droplets from bees fed either sunflower or control (buckwheat) pollen. Preliminary findings show that regardless of infection, sunflower pollen consumption results in feces persisting 25% longer than the control. This suggests that sunflower pollen may alter fecal composition. We are performing a proteomic analysis investigating functional immune activity of B. impatiens in response to diet and pathogen infection. We predict that consumption of sunflower pollen will result in increased expression of immune related proteins in the guts of bees, regardless of infection. Increased expression of immune proteins would suggest that sunflower pollen protects bees from C. bombi infections by increasing host resistance.