ALTERNATE HOSTS OF THE RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE) IN NORTHEASTERN COLORADO

A 2-yr survey of 25 grass species in northeastern Colorado showed that crested wheatgrass, Agropyron cristatum (L.) Gaertn., and Canada wildrye, Elymus canadensis (L.), were dominant hosts of the Russian wheat aphid, Diuraphis noxia (Mordvilko). These two grasses served as hosts between the time winter wheat was harvested and planted. Russian wheat aphids showed greater life stage diversity when collected from Canada wildrye compared with any other grass species. Several additional perennial and annual grasses were able to support Russian wheat aphids but less consistently and in lower numbers. Russian wheat aphids were found on a wide range of grass species early in the summer. Thereafter, numbers of Russian wheat aphid hosts decreased as the summer progressed. Total numbers of Russian wheat aphids collected from all grass hosts for 1989 were seven times greater than for 1988. The 1989 survey indicated a more suitable year for Russian wheat aphid migratory flight, host seeking, and survival. Russian wheat aphid suction trap captures corresponded with grass survey data and further verified the differences between the two survey years.