Carpenter bee microbiomes are distinctive and related to microbiomes of honey bees and bumble bees

Many eusocial corbiculate bees, including bumble bees and honey bees possess a stable gut microbiome that is transmitted socially between nest mates and that has been shown to support food digestion and protection from pathogens. Solitary bees, however, typically have more variable microbiomes dominated by bacteria associated with pollen and nectar. Carpenter bees of the genus Xylocopa live in solitary or shared nesting-sites, so interactions with other bees are less frequent. We characterized the gut microbiomes for Xylocopa micans, X. mexicanorum, X. tabaniformis parkinsoniae, and X. virginica at several sites in central Texas. Each carpenter bee species had conserved microbiomes that were dominated by bacteria from lineages associated with guts of social bees or other insects. Microbiomes were similar across three Xylocopa species and included lineages in the families Bifidobacteriaceae, Orbaceae, and Lactobacillaceae. In contrast, X. virginica had a distinct microbiome dominated by the genus Bombilactobacillus, a genus abundant in the guts of honey bees and bumble bees. Phylogenetic analyses support a past transfer of bacterial lineages into Xylocopa from bumble bees or honey bees. Recently published work supports these findings; six additional species of Xylocopa from California, Japan and China all harbor conserved microbiomes, and two species of Lactobacillacae isolated from two species of Xylocopa in Japan have been placed in a novel genus, Xylocopilactobacillus. Whether the characteristic microbiomes provide benefits to Xylocopa hosts, as shown for eusocial bees, is unknown and awaits further research.