Neonicotinoid Seed Treatments Influence Soil Nematode Taxonomic Composition and the Soil Microbial Co-occurrence Networks

Neonicotinoid insecticides are widely used to control early-season and foliar-feeding pests. Some studies have revealed their non-target impacts on pollinators and other invertebrates, but few investigated their effects on soil microbiota. Given the crucial role of soil prokaryotic and eukaryotic microbial communities in agroecosystem regulation and their contribution to soil fertility, it is critical to understand their structure and changes in response to disturbances such as pesticide application. Among these communities, free-living nematodes have the potential to indicate the ecological changes in soil caused by environmental stress and have a key role in forming and modulating soil microbial composition and function by feeding on other soil microorganisms or interacting with them. Here, we used 18S rRNA gene amplicon sequencing to characterize the effects of neonicotinoids on soil nematode communities in a three-year soybean/corn crop rotation in Quebec, Canada. We also quantified the changes in nematode-bacteria co-occurrence networks in soil exposed to neonicotinoids. We found that neonicotinoid seed treatment significantly explained variation in nematode community composition and affected the relative abundance of some nematode families, such as a decrease in the omnivorous family Dorylaimidae in neonicotinoid-treated samples. Moreover, neonicotinoids altered the patterns of nematode-bacteria co-occurrence, including the structure and taxonomic composition of the networks. However, it is unclear whether neonicotinoids affected bacterial co-occurrence networks directly or indirectly by affecting nematodes that feed on bacteria. Further research is needed to understand how neonicotinoids affect nematodes and the role of nematodes in microbial network variation in soil exposed to neonicotinoids.