Predator biodiversity strengthens aphid suppression across single- and multiple-species prey communities

A positive relationship between predator biodiversity and improved pest suppression might be most clearly realized when several prey species are present, if a diversified prey base allows complementarity among predators to be realized. In two field experiments we manipulated diversity both within a guild of predatory insects (one versus four predator species) and among their herbivore prey (one versus two aphid species present). The strength of aphid suppression always increased with greater predator biodiversity, but this effect was independent of prey species diversity or identity, and no niche differentiation by aphid species was apparent among the predator species. This suggests that either niche partitioning among predators occurred but was not based on prey species identity or that the benefits of predator diversity for biological control were mediated by interactions within the predator community, such that a diverse resource base was not necessary to yield a positive relationship between predator biodiversity and effective herbivore suppression.