Seasonal abundance of Russian wheat aphid (Homoptera : aphididae) on noncultivated perennial grasses

In the northern part of the Russian wheat aphids (Diuraphis noxia [Mordvilk o]) (Homoptera: Aphididae) North American range (the High Plains east of th e Rocky Mountains), over summering of the aphid is likely during late summe r when cultivated small grains are not in production if volunteer small gra ins or noncultivated perennial hosts are present. Grasses of eight genera w ere sampled from a small plot in Laramie, WY. 1995-1997, to assess field pr esence of Russian wheat aphid on noncultivated grass hosts during summer wh en small grains are not in production. Significantly greater densities of R ussian wheat aphid were found on spring barley (Hordeum vulgare L.) than on six perennial grasses each summer. In 1995, when perennial plants were in their first year of growth, significant differences in aphid densities were found among noncultivated perennial grasses, with greater densities on cre sted wheatgrass (Agropyron cristatum [L.] Gaertner x A. desertorum [Fischer ex Link] Shultes) than on smooth brume (Bromus inermis Leyss.) and slender wheatgrass (Elymus trachycaulus [Link] Gould & Shinners). After plant vern alization during the winters of 1996 and 1997, densities of Russian wheat a phid were similar on all perennial hosts. Volunteer spring barley in partic ular appeared important in supporting Russian wheat aphid during late summe r, although the cool-season perennial hosts were also capable of hosting th e aphid. Until mid-September, aphids are likely to occur on spring barley a nd perennial grass hosts if abiotic conditions are favorable for plant grow th, providing a local source of aphids to move onto newly emerged winter gr ains.