Performance of the Russian Wheat Aphid (Homoptera: Aphididae) on Perennial Range Grasses: Effects of Previous Defoliation

Abstract

We determined whether early-season defoliation of range grasses affected the subsequent suitability of these plants for the Russian wheat aphid, Diuraphis noxia (Mordvilko). Grazing was simulated by clipping six grass species in northern Utah in April 1992. Aphid population growth was higher on clipped plants than on control plants, especially during the oversummering period when aphids may rely on range grasses as alternate hosts. Aphids suffered complete mortality on 28% of control plants during this period but failed to establish themselves on only 2% of clipped plants. Defoliation increased plant nitrogen and water content, and differences in total nitrogen between clipped and control plants were positively correlated with differences in aphid density. Spring grazing may generally increase the susceptibility of grasses to D. noxia ; an exception to this pattern was Indian ricegrass, which responds to defoliation by greater reproduction instead of rapid vegetative growth.