Increasing amount and quality of green infrastructures at different scales promotes biological control in agricultural landscapes

Green infrastructures are key elements for the delivery of ecosystem services in agricultural landscapes. However, how to combine quality and quantity of green infrastructures at multiple spatial scales to optimize the delivery of ecosystem services remains largely unknown. In this study, we investigated how hedgerow amount in the landscape modulated the local effect of grassland quality (plant species richness) on the spillover of biological pest control services in adjacent sunflower fields. We quantified biological pest control and predator communities in 23 adjacent sunflower-grassland field couples selected along two uncorrelated gradients: a gradient of plant species richness in grassland and a gradient of hedge length in the landscape. Our study shows that increasing the amount or the quality of green infrastructures can enhance biological pest control in adjacent crops but that the effects depend on the pest considered. We found that weed seed predation depends only on hedge length in the large scale landscape, while aphid predation depends on plant species richness in the adjacent grassland and on the hedge length in the immediate landscape. Also, the abundance of spiders affects aphid predation suggesting a key role of this functional group for controlling aphids in sunflower fields. This study suggests that management options based on increasing local plant species richness should be prioritized in landscapes with low amount of hedgerows, and confirms the fact that increasing hedgerow networks should promote pest control services.