Relationships between natural enemy diversity and biological control.

Natural enemy diversity generally strengthens biological control, but individual studies have found everything from positive to negative effects. We discuss the factors that promote these different outcomes. We argue that a trait-based approach is helpful to improve our understanding of the relationship between enemy diversity and biological control, and suggest that enemy diversity is likely to be particularly important as an insurance against effects of climate change. Future research should increase the scale and ecological realism of enemy diversity studies, and consider both the strength and stability of biological control. Such research is likely to reveal even stronger evidence that conserving enemy biodiversity will improve biological pest control.