Soil Environments Influence Gut Prokaryotic Communities in the Larvae of the Invasive Japanese Beetle Popillia japonica Newman

Abstract

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 importance of the larval gut microbial community in driving the behavior, physiology, and nutritional ecology of this invasive insect, the role of soil biological and physicochemical characteristics in shaping this community are relatively unknown. Our objectives were to (1) characterize the degree to which larval gut microbial communities are environmentally acquired, (2) examine the combined effects of the gut region (i.e., midgut, hindgut) and local soil environments on gut microbial communities, and (3) search for soil physicochemical correlates that could be useful in future studies aimed at characterizing gut microbial community variation in soil-dwelling scarabs. Gut communities from neonates that were never in contact with the soil were different from gut communities of third instar larvae collected from the field, with neonate gut communities being significantly less rich and diverse. The influence of compartment (soil, midgut, or hindgut) on prokaryotic α- and β-diversity varied with location, suggesting that JB larval gut communities are at least partially shaped by the local environment even though the influence of compartment was more pronounced. Midgut microbiota contained transient communities that varied with the surrounding soil environment whereas hindgut microbiota was more conserved. Prokaryotic communities in the hindgut clustered separately from those of soil and midgut, which displayed greater interspersion in ordination space. Soil cation exchange capacity, organic matter, water holding capacity, and texture were moderately correlated (≥29%) with gut prokaryotic microbial composition, especially within the midgut. Findings suggest that microbial communities associated with the JB gut are partially a function of adaptation to local soil environments. However, conditions within each gut compartment appear to shape those communities in transit through the alimentary canal.

Larvae of an invasive scarab increase greenhouse gas emissions from soils and recruit gut mycobiota involved in C and N transformations

“…At another location (Throckmorton-Purdue Agricultural Center, TPAC), infestations were created artificially on agricultural soil subjected to 30+ years of rotational corn and soybean. These infestations were created by caging JB adults on the soil and allowing them to oviposit as described elsewhere ( Avila-Arias et al, 2022 ). A set of uninfested plots were included in the design.…”

“…To characterize the variation in the gut fungal community of third instar JB larval and infested soil, samples (three biological replicates for each sample category) were collected from seven locations across Indiana and Wisconsin, United States ( Table 1 ). Third instar larvae and soil samples were collected as described elsewhere ( Avila-Arias et al, 2022 ). Briefly, third instar larvae were collected from the soil at naturally infested locations using a soil coring device.…”

“…Third instar larval gut dissection was performed as described elsewhere ( Avila-Arias et al, 2022 ). Briefly, third instar larvae were identified to species based on the conformation of the raster pattern using Richmond (2022) as a guide, cleaned and surface disinfected using 70% ethanol.…”

“…Resultingly, JB larvae accelerate root inputs to soil and stimulate the decomposition of existing soil organic matter ( Gan et al, 2018 ). The presence of robust, soil-derived prokaryotic communities in the JB gut include heterotrophic, ammonia-oxidizing, and methanogenic prokaryotic microbes ( Chouaia et al, 2019 ; Avila-Arias et al, 2022 ), potentially capable of promoting GHG emissions. To date, little research has explored the community of eukaryotic microbes associated with the JB larval gut.…”

“…Further, we characterized gut fungal communities associated with soil-dwelling JB larvae and examined how local soil environments influence variation in the composition of these communities within different compartments of the JB gut. Due to the highly invasive nature of JB and the intense larval activity below-ground, we hypothesize that JB infestation increases GHG emission from soil, and that mycobiota associated with the JB alimentary canal is a function of adaptation to local soil environments, as seen for prokaryotic communities ( Avila-Arias et al, 2022 ).…”