Greenhouse and field experiments were conducted to determine whether host-plant species affects the ability of a generalist predator to reduce populations of the Russian wheat aphid, Diuraphis noxia (Mordvilko). Aphid colonies were allowed to develop on six species of cool-season grasses for 10 days, after which half of the plants received five neonate larvae of the common green lacewing, Chrysoperla carnea (Stephens). Lacewing larvae substantially reduced aphid density on both grass seedlings (in the greenhouse) and mature plants (in the field). The level of control varied among grass species, however. Aphid populations were reduced to zero or near zero on two slender-leaved grasses (Indian ricegrass and bluebunch wheatgrass), but were maintained at moderate densities on a pubescent cultivar of intermediate wheatgrass. Mechanisms underlying this tri-trophic interaction are unknown, but plant morphology may play an important role because of the "leaf-galling" habit of D. noxia.