The causes of soil microbiome mediated insect pest suppression in organic agroecosystems

Microbial communities play a crucial role in regulating insect populations in natural and agricultural systems. Metabarcoding has enabled characterization of microbial communities across ecosystems, yet unraveling the variables that drive microbial diversity and ecosystem function remains challenging. Microbial communities in agroecosystems are further shaped by social, economic, demographic, and farming system characteristics (e.g., farm size). Specifically, farmer environmental perceptions can influence ecosystem services through variable adoption of farming practices (e.g., no-tillage). Here we use a survey of 85 organic farmers, soil microbiome metabarcoding, structural equation modeling, and pest suppression experiments to (1) examine farming practices mediating soil microbial communities; (2) determine relationships between insect pest suppression and the soil microbiome; and (3) construct a socio-ecological model for microbiome mediated insect pest management on farms. We show the dimensions of microbial diversity (e.g., alpha and beta diversity) were driven by different farming practices with divergent responses for fungi and bacteria. These microbiome responses were often phylogenetically structured, with several dimensions of microbial diversity connected to plant defenses and insect pest suppression. Underlying these ecological variables, our structural equation models indicated that farmer perceptions of the soil microbiome had indirect effects on insect pests by mediating the adoption of farming practices. Taken together, our findings show that suites of practices foster the soil microbiome and ecosystem services in farms. However, we show socio-ecological models may be key to promoting the soil microbiome and insect pest management across agroecosystems, because they account for the ecological, economic, and social variables shaping farming practice adoption.