Indirect effects of predator diversity on a vector-borne plant pathogen

Predators may indirectly influence the occurrence of disease by directly altering the abundance and/or behavior of vectors that are responsible for pathogen transmission. We evaluated the impact of altered predator diversity on the bird cherry-oat aphid (Rhopalosiphum padi), a vector of barley yellow dwarf virus in cereal grains, to ultimately determine if predator diversity effects on aphid abundance, distribution, or feeding behavior cascade down to influence the prevalence of this pathogen in wheat. Overall, we found that predators had strong negative impacts on vector abundance and pathogen prevalence. When we focused on the effect of predator diversity, we found that a diverse group of predators reduced vector abundance to a greater extent than did single-species assemblages, however diverse treatments did not differ from single-species treatments in the spatial occurrence of vectors across the habitat, or in the proportion of wheat plants that were infected. When we evaluated vector feeding behavior we found that predators stimulated vector movement similarly across diversity treatments, resulting in more frequent interruptions to vector feeding sessions when predators were present. We therefore conclude that predators may indirectly influence pathogen prevalence in a host population by directly impacting vectors, and a key mechanism by which this influence may be exerted is via impacts to vector feeding behavior, which can further alter the efficiency of pathogen transmission from host to host.