Yeasts Harbored by Vespine Wasps in the Pacific Northwest.

The ecological role of social wasps has been extensively studied, but little is known about symbiotic relationships of these wasps with microbes. Recently, it was shown that vespid wasps in Europe carry yeasts, predominantly Saccharomyces cerevisiae, in their gastrointestinal (GI) tract. Interestingly, this niche allowed for sexual recombination of yeasts to occur and the formation of novel hybrid species. Our goals were 1) to survey the GI tract of eusocial wasps in the Pacific Northwest for the presence of yeasts and 2) to compare the diversity of such yeasts to that described for wasps in Europe. The GI tracts of 19 individual wasps from five species were plated, and 27 yeast-like colonies were identified to the species level. Yeasts in the genera Lachancea and Hanseniaspora each comprised ∼30% of the isolates; ∼25% were identified as Metschnikowia spp., with the remaining 10% belonging to Rhodotorula. Four bacterial isolates were identified as Escherichia coli, Enterococcus faecalis, and two isolates of Stenotrophomonas maltophilia. Yeasts were present at all life stages of the wasps except for two unfed gynes of Dolichovespula maculata (L.) that contained only bacteria. The presence of a particular yeast species was not correlated with any wasp species. Furthermore, S. cerevisiae was not found in any wasp species. This highlights an interesting difference in the life cycle of both S. cerevisiae and wasps in Europe and the Pacific Northwest, and prompts further studies on the interactions of these microbes with their host wasps.