Antimicrobial properties of glands in solitary ground nesting bees may control brood cell microbial community

Almost all solitary bees practice mass provisioning, stockpiling resources for the entirety of their offspring's growth inside a sealed chamber. Along with the resources provided are a haphazard mix of microbes, often picked up from the environment while foraging and ranging from saprophytes, to putative commensals, to pathogens. Additionally, ground nesting bees also face a range of environmental microbes that may invade the brood cell through the soil. Bee provisions, however, rarely show the detrimental takeover of microbes and the death of larvae due to mold or pathogen growth is relatively rare. While other mass provisioning insects such as bee wolves have been shown to apply antimicrobial secretions to their brood cells to inhibit microbial growth, it is unknown if the same is true in solitary bees. We investigated if the glandular secretions of the dufour's gland, used by many ground nesting bees to line their brood cells, may contain antimicrobial chemicals that act to select on the microbial community and keep soil pathogens from infiltrating the brood cell. Using in vitro 96 well optical growth assays, we found that the dufour's gland of certain bees can inhibit and reduce the growth of tested environmental microbes.