Plant-pollinator interactions influence pathogenic disease transmission in bumble bees

Plant-pollinator interactions have the potential to shape dynamics of pathogenic disease transmission between pollinators, and flowers may function as hotspots of transmission. Plant species have flowers with different morphology and floral architecture, but how does this variation shape disease transmission in pollinators? Answering this question requires us to identify plant traits associated with high pollinator visitation, fecal deposition, pathogen survival and acquisition. Using the common eastern bumblebee, Bombus impatiens, a trypanosomatid gut pathogen, Crithidia bombi, and 7 morphologically different floral species commonly featured in pollinator seed mixes, we observed locations of infected bumblebee defecation on floral species, pathogen survival over time on different plant tissues, and potential for uninfected bumblebees to acquire disease at locations of defecation. Further, we also used a manipulative experiment to assess visitation and fecal deposition patterns on two floral architecture types, stacked and carpeted, in two morphologically similar legume species (Securigera varia and Lotus corniculatus). We found a significantly high fecal deposition on leaves. However, defecation was not significantly different between plant species. In the experimental manipulation, the interaction between floral architecture and location of deposition was significant, indicating that floral architecture also influences fecal deposition patterns. In terms of pathogen survival at locations of defecation, time was the only significant predictor. We conclude that pollinators show differences in defecation patterns on different plant parts and floral architecture, and time is an important factor in determining whether susceptible hosts contact live pathogens in feces, which is necessary for transmission to occur.