(2nd Place) The impact of pesticides, floral resources, and land use on wild bee microbiomes across an urban-rural divide

Increased anthropogenic activities are causing changes in the environment and climate that threaten bees and their microbiota. Characterizing the microbiome of wild bees from urban areas creates opportunities to understand how these important pollinators and their microbiota are adapting to increased land use development. Further, directly comparing these to the microbiome of neighboring rural populations offers the unique ability to consider how agriculture, which results in an array of different floral resources and the application of commercial pesticides, are affecting wild bee microbiota. Our study compares the microbiome and floral resources associated with wild bees located in urban and rural contexts in and around Toronto, Canada. We used metabarcoding of the 16S, ITS, and rbcL regions in order to characterize the bacteria, fungi, and plants found in the small carpenter bee Ceratina calcarata and their pollen provisions. We found that urban bees harbour different microbiota than their rural counterparts, being underrepresented in important beneficial bacteria such as Apilactobacillus, but also exhibiting higher pathogen loads. Pollen provisions of both rural and urban bees presented pesticides such as neonicotinoids and fungicides, which significantly influenced the microbial diversity within the provisions. This establishment of different microbial communities and plant-pollinator interactions suggests that the overall microbiome and its stability varies in different environments, highlighting populations in which microbial changes may threaten bee health.