Landscape-level crop diversity benefits biological pest control.

Abstract

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. 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 × SNH), bird predation (yes/no) and temporal change (three surveys) on six spatial scales (100-3,000 m). 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. 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. Synthesis and applications. Our study shows that landscape-level crop diversification can improve biological control in agroecosystems. Therefore, increased crop diversity could lower dependence on insecticides while enhancing yield stability through ecological intensification of farming. We also highlight the need to assess biological control rather than natural enemy abundances to avoid bias due to sampling artefacts or species interactions. Finally, simple measures of crop diversity (e.g. "effective number of crop types") help in science communication and the development of farm management guidelines.

Key words

• agricultural land
• arthropod pests
• biodiversity
• biological control
• cages
• diversification
• ecology
• ecosystem services
• ecosystems
• effects
• farm management
• guidelines
• insect pests
• insecticides
• interactions
• landscape
• natural enemies
• parasites
• parasitoids
• pest control
• pesticides
• pests
• predation
• predators
• surveys
• temporal variation
• wheat
• yields