Do alternative prey disrupt or enhance pest consumption? A case study with a flexibly-foraging, sit-and-wait predator

Generalist predators can contribute significantly to pest suppression in agricultural systems.  However, the complexity of functional roles of predators in trophic webs can also compromise their usefulness in biological control.  For example, in the presence of high-quality, non-pest prey, generalist predators may consume fewer pest prey.  However, few studies have investigated the impacts of alternative prey on pest consumption from a behavioral perspective, and the role of predator foraging tactics in mediating predator-pest interactions is currently unclear.  In this study, two behavioral trials were performed to examine the behavior of a flexibly-foraging generalist predator (a web-building spider) in response to pest and non-pest prey.  In laboratory two-choice trials, spiders utilized different foraging tactics to capture pest and non-pest prey: webs were frequently constructed to capture non-pest Collembola, but active-foraging tactics were more frequently used to capture aphid pests.  In laboratory no-choice trials, aphid pests and Collembola alternative prey were provided in a factorial design.  Spider micro-site selection varied by treatment: when aphids were present, spiders occasionally utilized the stems of aphid host plants for web attachments, but did not utilize plant stems when aphids were not present.  This suggests that spiders were optimizing web placement to capture aphids.  Predation rates on pest and non-pest prey in no-choice tests were validated using PCR gut-content analyses, demonstrating the compatibility of aphid consumption with web-based foraging tactics and suggesting that alternative prey may not disrupt pest suppression by this species.