Non-consumptive effects of the predatory beetle Delphastus catalinae (Coleoptera: Coccinellidae) on habitat use patterns of adult whitefly Bemisia argentifolii (Hemiptera: Aleyrodidae)

Abstract

This study examined habitat use patterns by adult whiteflies, Bemisia argentifolii Bellows and Perring, in response to predators, Delphastus catalinae (Horn), at different spatial scales. When female whiteflies were confined to small arenas with leaf discs from which they could not escape, whiteflies significantly delayed settling on leaf discs when predators were present compared to when no predators were introduced. The presence of D. catalinae altered the vertical distribution of adult whiteflies (sex ratio = 1:1) on cucumber plants; adult whiteflies moved upward faster over time within the plant canopy when predators were present mainly on the lower leaves of the plants compared to whiteflies on plants without predators. Most D. catalinae remained in the lower parts of the plants during the experiment. Therefore, we inferred that female whiteflies more quickly moved to the upper plant strata to reduce the risk of predation of their progeny; this would induce subsequent movement of males seeking mates. Introduction of D. catalinae onto a cucumber plant with high whitefly density did not cause increased dispersal of adult whiteflies (sex ratio = 1:1) into neighboring uninfested plants. The results indicate that predator-avoidance behaviors by adult B. argentifolii differed at different spatial scales. The predator-avoidance behavior may have a negative impact at the within-plant scale by inducing more whiteflies to move into upper plant strata. However, the effect of predators on the among-plant dispersal of whiteflies was not significant.