The inherent complexity of soil and foliar predators for greenhouse biological control

Abstract

In greenhouse systems it is commonplace to release a suite of predators or parasitoids to combat pest populations that grow in both the vegetative portion of plants and soil. For instance, to control thrips and fly pests, a combination of Neoseiulus cucumeris (Oudemans 1930), a foliar predatory mite, Stratiolaelaps miles (Berlese 1892), a soil dwelling mite and Dalotia coriaria (Kraatz 1856), a soil dwelling beetle, show efficacy for controlling all life-stages. However, when introduced biological control agents overlap in their distributions and diet, there is the potential for competition or intraguild predation. Frequently studies of intraguild interactions involve isolation of one pest or prey and a host of predators, here we conducted an initially open greenhouse experiment in a marigold system and allowed communities to assemble. We measured the community responses in the soil and foliar habitat strata to a fully replicated factorial design of all combinations of three common greenhouse predators, N. cucumeris, S. miles and D. coriaria. Over 288,158 arthropods were recovered from this six-week experiment resulting in unique soil and foliar communities of introduced predators, greenhouse arthropods, and pest life-stages. In the foliar habitat strata, spider mite populations rapidly overwhelmed the initial focus on thrips, indicating the importance of pest interactions for determining the efficacy of biological control. Overlap of predator populations occurred in the soil strata, which led to complex intraguild interactions. Results provide further evidence that separation of introduced predators and availability of alternative prey in greenhouse systems is important for managing potential agonistic interactions.