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Résumé :
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In the northern part of the Russian wheat aphids (Diuraphis noxia [Mordvilko]) (Homoptera: Aphididae) North American range (the High Plains east of the Rocky Mountains), over summering of the aphid is likely during late summer when cultivated small grains are not in production if volunteer small grains or noncultivated perennial hosts are present. Grasses of eight genera were sampled from a small plot in Laramie, WY. 1995-1997, to assess field presence of Russian wheat aphid on noncultivated grass hosts during summer when small grains are not in production. Significantly greater densities of Russian 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 crested 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 vernalization during the winters of 1996 and 1997, densities of Russian wheat aphid were similar on all perennial hosts. Volunteer spring barley in particular appeared important in supporting Russian wheat aphid during late summer, although the cool-season perennial hosts were also capable of hosting the aphid. Until mid-September, aphids are likely to occur on spring barley and perennial grass hosts if abiotic conditions are favorable for plant growth, providing a local source of aphids to move onto newly emerged winter grains.
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