We compared the effectiveness of generalist predators in reducing populations of the Russian wheat aphid, Diuraphis noxia (Mordvilko), on range grasses that differ in leaf architecture. Crested wheatgrass, Agropyron desertorum, produces relatively broad leaves and, like wheat, provides aphids with rolled leaves as potential refuges from natural enemies; Indian ricegrass, Oryzopsis hymenoides, bears linear, involute leaves that are usually too narrow to permit aphid aggregations within leaf rolls. We established aphid populations on each host and then introduced either neonate larvae of the lacewing Chrysoperla plorabunda (Fitch) or adults of the ladybird beetle Propylea quatuordecimpunctata L. On seedlings, there was an interaction between the effects of predator species and host-plant species; beetles were less effective on crested wheatgrass than on Indian ricegrass, but lacewings eliminated or nearly eliminated aphid populations on both hosts. On whole plants in the field, both predators tended to be more effective on Indian ricegrass than on crested wheatgrass. In all experiments, lacewing larvae were superior to beetles in causing extinction of aphid populations. These results are consistent with behavioral observations of foraging predators, and suggest that the host-plant effects on the 3rd trophic level can depend on predator species as well as plant stage