Microbiome Dynamics Influence Larval Nutrition, Survival and Endosymbiont Abundance in the Solitary Bee, Megachile rotundata

Social bees have been extensively studied for their gut microbial functions, but the significance of the gut microbiota in solitary bees remain less explored. Solitary bee, Megachile rotundata F. females provision their offspring with pollen from various plant species, harboring a diverse microbial community that colonizes larvae guts. The Apilactobacillus is the most abundant microbe, but evidence concerning the effects of Apilactobacillus and other provision microbes on growth and survival are lacking. We hypothesized that the presence of the gut microbiome, and Apilactobacullus in particular, would enhance larval and prepupal development, weight, and survival. We reared larvae on pollen provisions with naturally collected microbial communities (Natural pollen) or devoid of microbial communities (Sterile pollen). We also assessed the impact of introducing Apilactobacillus micheneri by adding it to both types of pollen provisions. Feeding larvae with sterile pollen + A. micheneri led to the highest mortality rate, followed by natural pollen + A. micheneri, sterile pollen. Larval development was significantly delayed in groups fed sterile pollen and sterile pollen + A. micheneri compared to the control. Interestingly, larval and prepupal weights did not significantly differ across treatments compared to natural pollen-fed larvae. 16S rRNA gene sequencing found a dominance of endosymbiont Sodalis when A. micheneri was introduced to natural pollen. The presence of Sodalis with abundant A. micheneri suggests potential crosstalk between both, shaping bee nutrition and health. Hence, this study highlights that the reliance on non-host specific environmental bacteria may not impact fitness of M. rotundata. Keywords: Megachile rotundata, Apilactobacillus micheneri, Sodalis, solitary bee, bee health and nutrition, bee microbiome, growth, survival