The bacterial community associated with the solitary resin bee <i>Megachile tosticauda</i> throughout its life cycle

Unlike in eusocial bees where the identity, acquisition, and function of symbiotic microbes are well understood, little is known about the relationships formed between solitary bees and bacteria. Assessing the potential role of microbes in solitary bee health is important, especially in the face of global bee declines. Early evidence suggests solitary bee microbiomes differ between bee species and development stages, but the reported bacteria are often indistinguishable from environmental taxa. Here, we use metabarcoding of the 16S rRNA gene to characterize the bacterial communities associated with solitary resin bee Megachile tosticauda. We describe the microbiome at different life cycle stages, and within pollen provisions, and investigate indirect inheritance from nesting substrate upon eclosion. The microbiome of adult M. tosticauda was consistent between samples, and the bacterial composition of larval pollen supplies changed with progressing larval development. In wild adults and pollen provisions, the genus Acinetobacter-a common nectar associate-dominated the communities. In prepupae and frass, Tyzzerella dominated, a genus that has been found in a number of other immature bee systems. Intriguingly, while wild adults did not harbour Tyzzerella, all bees that had newly emerged from the nest did. The combined observations show that M. tosticauda acquire their bacterial community from the environment, and Tyzzerella may represent a beneficial symbiont for mature brood.