Prey and predator biodiversity mediate aphid consumption by generalists

Abstract Greater arthropod diversity may promote biological control by bringing together predator species that occupy complementary feeding niches. Diverse prey communities could further accentuate such niche differences and decrease predator-predator antagonism. However, much evidence of these effects comes from simple experiments that do not reflect the ecological complexity of real agricultural fields. Here we used molecular gut-content analysis to examine how predator and prey biodiversity impacted consumption of aphids by two generalists, Nabis sp. and Geocoris sp., in potato (Solanum tuberosum) crops. We show that both predator species were more likely to have fed on aphids when they foraged in fields with greater overall predator richness, an apparent benefit of predator biodiversity for aphid biocontrol consistent with greater complementarity. However, Geocoris saw less-frequent aphid predation with increasing predator evenness, perhaps because they foraged less when dangerous intraguild predators were common. For both predator species, higher thrips (Frankliniella occidentalis) abundance also correlated with greater aphid predation, as did higher total arthropod richness for Nabis. Altogether, beneficial complementarity appeared to be enhanced by greater predator or prey richness, although, for Geocoris, this was opposed by a negative effect of predator evenness. Strong prey-species-identity effects generally enhanced, rather than disrupted, aphid predation. Overall, the full diversity of biodiversity-biocontrol relationships suggested by smaller-scale experiments also appeared to be impactful in complex, working agricultural fields.