The Russian wheat aphid, Diuraphis noxia (Mordvilko), is a severe pest of wheat, Triticum aestivum L; barley, Hordeum vulgare L; other small grains; and grasses. Although the Russian wheat aphid is a significant pest of small grains, its feeding effects on grain yield and vegetative biomass in large-scale wheat fields have not been well documented. Data were collected for 3 years in dryland and irrigated wheat fields in Texas and Oklahoma. The insect reduced grain yield 50.2 to 82.9% and biomass by 55.4 to 76.5%. These results suggested that winter wheat suffers significant economic loss from Russian wheat aphid.