Landscape-level crop diversity benefits biological pest control

1. Landscape-level crop diversification is a promising tool for ecological intensification, whereby biodiversity and ecosystem services are enhanced, and pesticide applications reduced. Yet evidence for the effects of crop diversity at multiple scales and in different landscape contexts is lacking. Here, we investigate the potential benefits and context dependencies of multiscale crop diversity on natural enemies and overall biological control in winter wheat. Simultaneously, we examine the mediating effects of bird predation on aphid regulation in this system. 2. Eighteen conventional winter wheat fields were selected along two independent gradients of crop diversity and semi-natural habitat cover (SNH). We assessed biological control using a natural enemy exclusion experiment (Open Treatment, Bird Exclosure, Full Exclosure). Biological control, predator and parasitoid densities within cages were analysed as functions of landscape (crop diversity x SNH), bird predation (yes/no) and temporal change (three surveys) on six spatial scales (100-3,000 m). 3. Crop diversity rather than SNH enhanced aphid regulation in our study system. Biological control in fields with high landscape-level crop diversity was 8%-33% higher than in low-diversity landscapes, with main effects observed on scales <500 m. 4. Predator and parasitoid densities increased with crop diversity on small (100-250 m) and large (2,000-3,000 m) spatial scales respectively. Nevertheless, our findings suggest that natural enemies other than birds, parasitoids and aerial arthropods facilitated biological control.