Sharing the (fungal) load: Identifying areas of fungal community overlap between bees and flowers in cranberry agroecosystems

Social bees have received significant attention in the study of gut microbial activity, microbial filtering in nests components, and the transmission of microbes in highly trafficked areas, such as flowers.  However, the question of how these bee-microbe ecological interactions actualize in bee-dependent agricultural systems remains.  In cranberry agroecosystems, the blossom period is thought to be a vulnerable time for fungal pathogen infections, and the floral-fungal community may have implications for cranberry and bee health. This study aims to identify connections between the fungal associates of bees and blossoms in cranberry systems in Central Wisconsin.  We hypothesize that 1) cranberry blossoms, bees, and proximate wildflowers share many fungal associates, and that 2) flowers exposed to bees have greater fungal diversity and abundance compared to flowers sheltered from bees.  Cultures of cranberry blossoms, bees, and wildflowers, and bees produced 186 unique fungal morphotypes, representing 15 identified fungal genera. In culture, filamentous fungi, but not yeasts, had a higher frequency of association with cranberry blossoms visited by bees compared to blossoms in which bee visitation was prevented.  Additionally, Allantophomopsis, a genus represented in the cranberry fruit rot disease complex, was identified in cranberry blossoms and bees, but not nearby wildflowers.  Illumina sequencing data reveals unique fungal communities associated with cranberry flowers and visiting pollinators, including honey bees, bumble bee groups, and syrphid flies. This work indicates that the bees and flowers do share many fungal associates in cranberry systems, and pollinator visitation influences the fungal communities on cranberry blossoms.