Socially transmitted gut microbiota protect bumble bees against an intestinal parasite

TLDR

Populations of pollinators such as bumble bees and honey bees are declining worldwide, likely in part due to parasites, and a distinct resident bacterial community unique to these social bees has been identified. Exposure to nest‑mate feces after pupal eclosion is required for the establishment of the microbiota and its protective effect. The presence of the microbiota protects bumble bees from the parasite Crithidia bombi, as shown experimentally and in field data, indicating that social transmission of gut bacteria confers an extended immune phenotype that benefits bee health.

Abstract

Populations of important pollinators, such as bumble bees and honey bees, are declining at alarming rates worldwide. Parasites are likely contributing to this phenomenon. A distinct resident community of bacteria has recently been identified in bumble bees and honey bees that is not shared with related solitary bee species. We now show that the presence of these microbiota protects bee hosts against a widespread and highly virulent natural parasite ( Crithidia bombi ) in an experimental setting. We add further support to this antagonistic relationship from patterns found in field data. For the successful establishment of these microbiota and a protective effect, exposure to feces from nest mates was needed after pupal eclosion. Transmission of beneficial gut bacteria could therefore represent an important benefit of sociality. Our results stress the importance of considering the host microbiota as an “extended immune phenotype” in addition to the host immune system itself and provide a unique perspective to understanding bees in health and disease.