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Nonconsumptive Predator Effects and their Implications for Biological Control
Recently, it has been demonstrated in several predator-prey interactions that predators influence prey population dynamics by inducing behavioral changes in prey as well as by feeding on prey. Accumulating evidence supports that prey change habit use patterns and activity levels in repose to predation risks. In the studies reported here, we examined the resource use patterns by adult whitefly, Bemisia argentifolii (Hemiptera: Aleyrodidae) in response to its natural enemies. The first study examined whether, in the context of a trap crop system, differential predation risks among plants influence host choice patterns of adult whiteflies. We investigated whether whiteflies avoid natural enemies inhabiting a cash crop (poinsettia) and whether this behavior can be used to increase the movement of whiteflies to a trap crop (cucumber). Three natural enemies were tested: two predators, Amblyseius swirskii and Delphastus catalinae and a parasitoid Encarsia formosa. The presence of D. catalinae on cash crop induced significantly more whiteflies to disperse to predator-free trap crop, compared with cash crop with no predator. A. swirskii and E. formosa did not result in a significant increase. The second study examined habitat choice patterns by adult whiteflies in response to D. catalinae at different spatial scales. When female whiteflies were confined in small leaf-disc arenas, whiteflies significantly delayed settling on leaf-discs with predators compared those with no predators. The presence of D. catalinae altered the vertical distribution of whiteflies on cucumber plants. Whiteflies moved upward faster over time within the plant canopy when predator were present at lower canopy compared with plants with no predator. However, D. catalinae did not result in elevated between-plant movement of whiteflies in the greenhouse, compared with that with no predator. Predator avoidance behavior by adult whiteflies should be considered in the development of biological control programs.
