Landscape composition and food web complexity jointly shape on-farm biological control services

In agricultural landscape mosaics, non-crop habitat affects pest-natural enemy communities, their dynamic interactions and ultimate ecosystem service delivery (i.e., biological pest control). The complex food web interactions driving landscape effects on ecosystem service delivery remain poorly understood. Here, drawing upon a 3-year dataset of parasitoid - hyperparasitoid food webs from 25 different agro-landscapes in the North China Plain, we assess the concurrent effects of landscape composition and (field-level) food web structure on aphid pest control in cotton. We employ piecewise structural equation modeling (SEM) to analyze postulated causal pathways explaining pest suppression. Landscape factors shape richness of both parasitoids and hyperparasitoids, in turn affecting food-web connectance and parasitism rate. Non-crop habitat also directly affected overall parasitoid numbers and indirectly bolstered pest control without mediation through the food web. Our work underscores a need to account for food web complexity when assessing insect-mediated biological control within agro-landscapes.