Environmentally acquired gut-associated bacteria are not critical for growth and survival in a solitary bee, Megachile rotundata

Authors: BRAR, GAGANDEEP - North Dakota State University; FLODEN, MADISON - North Dakota State University; MCFREDERICK, QUINN - University Of California, Riverside; Rajamohan, Arun; Yocum, George; BOWSHER, JULIA - University Of North Dakota

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2024
Publication Date: 9/18/2024
Citation: Brar, G., Floden, M., Mcfrederick, Q., Rajamohan, A., Yocum, G.D., Bowsher, J. 2024. Microbiome dynamics influence larval nutrition, survival and endosymbiont abundance in the solitary bee, Megachile rotundata. BMC Microbiology. https://doi.org/10.1128/aem.02076-23.

Interpretive Summary: Solitary bees, such as the alfalfa leaf cutting bees, are among the most important native pollinators of both the wild and agriculturally important plants. It is well known that among the social bees, such as the honey bees, the bee’s health would be afflicted, if the symbiotic bacterial composition in their gut is altered due to antibiotics or other stress. However, such studies have not been conducted on solitary bees. In our study, we challenged the alfalfa leaf cutting bee, Megachile rotundata, with both natural and sterile pollen as well as antibiotics. Bees fed with sterile pollen showed significantly higher mortality than in the other treatments. When the bees were fed with just one type of bacteria that is a predominant gut symbiont, it caused an overpopulation of an endosymbiont that lives within the bees’ cells. This points to the importance of a diverse gut microflora and emphasizes the importance of the symbiotic gut microflora which play an extremely important role in the growth and survival of the solitary bees. These native bees are vital to both the natural ecosystem as well as agriculture and food safety.

Technical Abstract: Social bees have been extensively studied for their gut microbial functions, but the significance of non-symbiotic microbiota in solitary bees and their potential functions remain less explored. Megachile rotundata F. is an important field crop pollinator. The females provision their offspring with pollen from various plant species containing a diverse community of microbes that may contribute to their health and survival. Despite the apparent importance of the microbial community, evidence concerning the direct and indirect effects of provision microbes on biology and survival are lacking in M. rotundata. We hypothesized that the individuals reared on the pollen lacking microbes will show significant reduction in the growth rate, survival, and mass of larvae, prepupae. We investigated the role of the gut microbiota in M. rotundata by conducting fitness bioassays and analyzing gut microbial communities through 16s rRNA gene sequencing. Larvae were reared on pollen provisions with naturally collected microbial communities or sterile pollen that are devoid of microbial communities. We also assessed the impact of introducing Apilactobacillus micheneri, a prevalent bacterial species in M. rotundata, on bee nutrition by adding it to both types of pollen provisions. Antibiotics cocktail was used as a positive control.