Geographic soil environments influence larval gut microbial communities in the invasive Japanese beetle Popillia japonica Newman (Coleoptera: Scarabaeidae)

Invasive scarab beetles, like the Japanese beetle Popillia japonica Newman (JB), spend most of their lives as larvae feeding in the soil matrix. Despite the potential role of gut microbial communities on the behavior, physiology, and nutritional ecology of these insects, relatively little is known about its composition or the role of environmental factors. With this study, we aimed to understand the role of soil biological and geochemical characteristics in shaping the gut microbial communities of JB larvae. We collected third instar JB larvae and their associated soil from seven locations across Indiana and Wisconsin, extracted metagenomic DNA, and amplified and sequenced the V4 region of the 16S ribosomal RNA. The physical and geochemical characteristics of the soil were also quantified. The influence of compartment (soil, midgut or hindgut) on prokaryotic α- and β-diversity varied with location, inferring that JB larval gut communities are shaped by environmental sourcing. Soil physical and geochemical characteristics were significant predictors of prokaryotic α-diversity. At the order level, core microbiomes from soil and midgut shared 17 taxa, while those of the midgut and hindgut shared 4. Core microbiomes of the soil and hindgut did not share any taxa exclusively, but Betaproteobacteriales was present in the core microbiome of all three compartments. Prokaryotic communities in the hindgut clustered separately from the other two compartments, which displayed greater interspersion in the ordination space. Our findings suggest that the microbial communities associated with each compartment appear to be a function of adaptation to the local soil environment.