Microbiome community structure and succession in the nests of two megachilid bee genera. Megachilid Microbiomes

Studies on honeybees have revealed bacterial taxa that are assumed to adopt key functions in the hive, in terms of nutrient uptake and immune responses. Despite the fact that solitary bees provide invaluable ecological services, the contribution of microbial communities to larval health, development and final fitness of adults is mainly unknown. To address this gap, we conducted a 16S meta-barcoding study including larvae and stored pollen in nest chambers from two different megachilid solitary bee genera. We tested how host taxonomy, environmental context and temporal stage during larval development determined the richness and composition of microbial communities. A total of 198 specimens of larvae as well as their pollen provisions from Osmia bicornis, Osmia caerulescens, Megachile rotundata and Megachile versicolor nests from different landscapes were investigated. Solitary bee microbiota in the nesting environment were much more diverse compared to eusocial bees and microbial communities were species-bound, rather than landscape dependent. We identified bacterial taxonomic units that showed consistent occurrence in the larvae and the pollen provisions within the same bee species and we unveiled others showing an abundance shift in line with progressing development and with that a dynamic change in overall bacterial community composition from egg-laying to hatching.