Environmentally acquired gut-associated bacteria are not critical for growth and survival in a solitary bee, Megachile rotundata.

Abstract

Social bees have been extensively studied for their gut microbial functions, but the significance of the gut microbiota in solitary bees remains less explored. Solitary bee, Megachile rotundata 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 Apilactobacillus in abundance would enhance larval and prepupal development, weight, and survival, while the absence of intact microbial communities was expected to have a negative impact on bee fitness. 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, and sterile pollen. Larval development was significantly delayed in groups fed with sterile pollen. 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 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 nonhost-specific environmental bacteria may not impact fitness of M. rotundata.IMPORTANCEThis study investigates the impact of environmentally acquired gut microbes of solitary bee fitness with insights into the microbial ecology of bee and their health. While the symbiotic microbiome is well-studied in social bees, the role of environmental acquired microbiota in solitary bees remains unclear. Assessing this relationship in a solitary pollinator, the leaf-cutting bee, Megachile rotundata, we discovered that this bee species does not depend on the diverse environmental bacteria found in pollen for either its larval growth or survival. Surprisingly, high concentrations of the most abundant pollen bacteria, Apilactobacillus micheneri did not consistently benefit bee fitness, but caused larval mortality. Our findings also suggest an interaction between Apilactobacillus and the Sodalis and perhaps their role in bee nutrition. Hence, this study provides significant insights that contribute to understanding the fitness, conservation, and pollination ecology of other solitary bee species in the future.