Biogeochemical interactions between an invasive scarab (Japanese beetle Popillia japonica Newman) and its subterranean environment

The goal of this study is to gain a better understanding of the interactions between invasive Japanese beetle (JB) larvae and their subterranean environment. Specific objectives include (1) quantifying the impact of JB larvae on soil microbial activity and functional diversity and (2) characterizing the microbiota associated with the JB larval gut and identifying linkages between soil and gut microbes. CO₂ flux and fluorescein diacetate (FDA) hydrolysis were measured in field and microcosm studies to provide surrogate measurements of the impact of JB larvae on microbial activity. Coarse changes in the functional diversity of soil microbes were also examined using phospholipid fatty acid analysis (PLFA). Preliminary findings support the idea that JB larvae do indeed cause significant and lasting changes to soil microbial diversity and activity by weakening soil rhizobial populations, shifting remaining microbial populations in favor of bacteria, and accelerating CO₂ liberation from the soil. Characterization of larval gut microbiota is ongoing, but it is apparent that JB larvae alter soil microbiota and are amenable to further study. Overall results so far suggest that invasive soil insects like JB may liberate large amounts of soil carbon, possibly reducing soil organic matter and increasing soil CO₂ emissions. Results also imply that interactions between JB larvae and the soil are, in part, microbially-mediated, which could have implications for pest management.