Floral and foliar source affect the bee nest microbial community

Authors: ROTHMAN, JASON - University Of California; ANDRIKOPOULOS, COREY - Utah State University; Cox-Foster, Diana; MCFREDERICK, QUINN - University Of California

Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2018
Publication Date: 12/14/2018
Citation: Rothman, J.A., Andrikopoulos, C., Cox-Foster, D.L., McFrederick, Q.S. 2018. Floral and foliar source affect the bee nest microbial community. Microbial Ecology. 78(2):506-516. https://doi.org/10.1007/s00248-018-1300-3.
DOI: https://doi.org/10.1007/s00248-018-1300-3

Interpretive Summary: Managed pollinators such as the alfalfa leafcutting bee, Megachile rotundata, are essential to the production of a wide variety of agricultural crops. These pollinators encounter a diverse array of microbes when foraging for food and nest-building materials on various plants. To test the hypothesis that the source of food and nest-building affects the composition of the bee-nest microbiome, we exposed M. rotundata adults to treatments that varied both floral and foliar sources (alfalfa and blue tansy as pollen sources; buckwheat and nasturtium leaves for nest building). We used molecular methods and DNA sequencing to determine the bacterial and fungal diversity of the bee nests. We found that nest microbial communities were significantly different for the different pollen and leaf sources, indicating that bees inoculate their nests with environmentally-derived microbes. We did not find evidence of interactions between the fungi and bacteria within our samples. Furthermore, both the bacterial and fungal communities were quite diverse and contained numerous species of known plant and bee pathogens that differed among the pollen and leaf sources. Our research indicates that bees deposit plant-associated microbes into their nests, including multiple plant pathogens such as smut fungi and bacteria that cause blight and wilt. The presence of plant pathogens in pollen provisions for bee larvae highlights the potential for bee nests to act as disease reservoirs across seasons. We suggest that future research should investigate the ability of bees to transmit pathogens from nest to host plant.

Technical Abstract: Managed pollinators such as the alfalfa leafcutting bee, Megachile rotundata, are essential to the production of a wide variety of agricultural crops. These pollinators encounter a diverse array of microbes when foraging for food and nest-building materials on various plants. To test the hypothesis that food and nest-building source affects the composition of the bee-nest microbiome, we exposed M. rotundata adults to treatments that varied both floral and foliar source in a 2 x 2 factorial design. We used 16S rRNA gene and Internally Transcribed Spacer (ITS) sequencing to capture the bacterial and fungal diversity of the bee nests. We found that nest microbial communities were significantly different between treatments, indicating that bees inoculate their nests with environmentally-derived microbes. We did not find evidence of interactions between the fungi and bacteria within our samples. Furthermore, both the bacterial and fungal communities were quite diverse and contained numerous Exact Sequence Variants (ESVs) of known plant and bee pathogens that differed based on treatment. Our research indicates that bees deposit plant-associated microbes into their nests, including multiple plant pathogens such as smut fungi and bacteria that cause blight and wilt. The presence of plant pathogens in larval pollen provisions highlights the potential for bee nests to act as disease reservoirs across seasons. We therefore suggest that future research should investigate the ability of bees to transmit pathogens from nest to host plant.