Russian wheat aphids, Diuraphis noxia (Mordvilko), were first detected in the United States in 1986. By September 1988, they had been found in 15 states and were considered a major threat to wheat ( Triticum aestivum L.) and barley ( Hordeum vulgare L.) grown in the United States and Canada. The economic importance of Russian wheat aphids will depend in part on their ability to use plant species as alternative and oversummering hosts. We therefore studied the survival and reproduction of Russian wheat aphids on numerous cool- and warm-season grasses, legumes, and forbs. Russian wheat aphids survived on 47 of 48 cool-season grass species, 18 of 32 warm-season grass species, and none of the 27 legumes or 17 forbs. Jointed goatgrass ( T. cylindncum (Host) Ces.) was the most suitable host, followed by barley, European dunegrass ( Elymus arenarius L.), and little barley ( H. pusillum Nutt.). Russian wheat aphids survived equally well on several cool-season grass species as they did on wheat. Compared with wheat, warm-season grass species were poor hosts for Russian wheat aphids. Many cool-season grasses were as preferred as the most favored warm-season grass species. The importance of Russian wheat aphids in North America has increased because they can survive on a broad range of cool- and warm-season grasses that grow throughout areas that produce barley and wheat.