Host Plant Alters the Shape of the Functional Response of an Aphid Predator (Coleoptera: Coccinellidae)

The response of the lady beetle Propylea quatuordecimpunctata (L.) to the density of the Russian wheat aphid, Diuraphis noxia (Mordvilko), was measured in petri dish arenas as well as on plants with divergent leaf architectures. Logistic regression was used to distinguish the shape of the functional response (type II or III), and nonlinear least-squares regression was used to estimate attack coefficients ( a ) and handling times ( T h ). In dishes, the behavior of both beetle larvae and adults closely conformed to a type II response. Estimates of a and T h on whole plants were considerably different from those obtained from dishes, and they also depended on plant species. Beetle adults consumed more aphids on the slender-leaved Indian ricegrass, Oryzopsis hymenoides (Roemer & Schultes) Ricker, than on the broad-leaved crested wheatgrass, Agropyron desertorum (Fisher ex Link) Schultes, at each aphid density. Moreover, logistic regression suggested a type II response on Indian ricegrass versus a type III (sigmoidal) response on crested wheatgrass. The complex response on crested wheatgrass may have been caused by density-dependent changes in the proportion of aphids in refuges (such as rolled leaves). By modifying the shapes and parameters of functional responses, plant traits can influence the stability of predator-prey dynamics and the success of biological control.