Effects of organic farming at different spatial scales on natural enemies of crop pests and pest predation levels

Biological control of pests by their natural enemies is considered a key process to reduce pesticide use in modern agricultural systems. Diversity of natural enemies and pest control levels have been shown to be enhanced in organic farming systems and in landscapes with high amount of semi-natural habitats, but the role of organic farming at the landscape scale remains little explored, especially on pest control levels. We investigated the effects of organic farming at the field and landscape scales on the diversity of predatory arthropods and on pest predation levels in 20 pairs of cereal crops located in bocage landscapes with varying proportion of area covered by organic farming in western France. Our results confirmed a strong effect of farming system at the field scale on arthropod diversity but not on pest predation levels. Arthropod diversity and pest predation were little or not influenced by organic farming at the landscape scale, but in some cases, by land-use diversity, grassland area and hedgerow densities. Our results suggest that the promotion of biological control in bocage landscapes might rely on both the local adoption of organic practices and on the maintenance of hedgerow habitats