Holley, J.-a. C.; Martin, A. N.; Pham, A. T.; Schlauch, J.; Moran, N. A.

Honey-feeding social bees, including honey bees and bumble bees, possess distinctive gut microbiomes that provide benefits to hosts, such as defense against pathogens and parasites. Microbiome members are transmitted through social interactions within colonies. The Mexican honey wasp (Brachygastra mellifica) represents an independent origin of honey-storing within a group of social Hymenoptera. Honey wasps feed on and store honey, but they prey on other insects as a protein source, and do not consume pollen as do bees. We surveyed the gut microbiomes of Mexican honey wasps across sites within Texas using 16S rRNA community profiling, and we estimated microbiome size using qPCR. For comparison, we also surveyed non-honey feeding wasps from six families, collected in the same region. We found that honey wasps have large microbiomes dominated by characteristic bacterial species, in contrast to other wasps, which had smaller, more variable microbiomes dominated by environmental bacteria. All honey wasps contained strains of Bifidobacterium and Bombilactobacillus that were closely related to symbionts of bumble bees and other bees, suggesting their acquisition via host-switching. Some individuals also harbored a close relative of Candidatus Schmidhempelia bombi (Orbaceae), an uncultured bumble bee symbiont, again suggesting host-switching. The most prevalent species was an uncultured Lactobacillus, related to L. acetotolerans, and potentially representing an independent acquisition of environmental Lactobacillus. The switch to honey feeding, combined with a highly social life history, appears to have facilitated the establishment of a microbiome resembling those of honey bee and bumble bees.