Russian wheat aphid populations have been monitored for the development of biotypes since the pest first appeared in the United States. Recent studies have confirmed the presence of five unique Russian wheat aphid biotypes in Colorado (Haley et al. 2004, Weiland et al. 2008), two of which were found on noncultivated grass hosts. The objective of this study was to confirm that while the Russian wheat aphid has undergone many changes as a species, the important grass hosts have not changed and are consistent each season. Species of noncultivated grass hosts were inventoried at field sites in four Colorado counties, Baca County, Montezuma County, Washington County, and Weld County, and the presence of Russian wheat aphids on the identified hosts was documented. Field sites were sampled in spring and fall 2005–2006 and the number and species of grass hosts were recorded and compared to look at host consistency across different geographic locations. Twenty-three grass species were identified across all counties. In Baca County, six of 14 grass species hosted Russian wheat aphids. In Montezuma County, Russian wheat aphids were found on five of 13 grass species. In Washington County, Russian wheat aphids were found on six of 18 grass species, and in Weld County, the aphid was found on five of eight grass species. Russian wheat aphids were collected most consistently from crested wheatgrass, Agropyron cristatum (L.) Gaertn., downy brome, Bromus tectorum L., Canada wildrye, Elymus canadensis L., and intermediate wheatgrass, Thinopyrum intermedium (Host) Barkw. & D.W.