Plant diversity increases potato leafhopper (Empoasca fabae) movement and vulnerability to predation

Understanding how changes in plant diversity affect agroecosystem functioning remains a key challenge. We examined how intercropping alfalfa, Medicago sativa, with forage grasses affects the potato leafhopper, Empoasca faba, its host plant (alfalfa), and the efficiency of a leafhopper predator, Nabis americoferus. In an open-field experiment, grasses reduced leafhopper abundance and damage to alfalfa. In a mesocosm experiment, Nabis was more effective at reducing leafhopper abundance, and protecting alfalfa from leafhopper damage, in an alfalfa-grass mixture than in a monoculture of alfalfa. In a series of laboratory experiments, we investigated mechanisms by which intercropping could enhance the efficiency of Nabis. Intercropping resulted in changes in plant architecture and the spatial distribution of leafhoppers, but there was little evidence that these factors influenced the efficiency of Nabis. Instead, (nonhost) grasses increased leafhopper movement, and Nabis captured leafhoppers more efficiently when the herbivores were more mobile. These results indicate that intercropping with nonhost plants increases leafhopper movement and vulnerability to predation, and reveal a novel mechanism by which plant diversity can reduce herbivory.