Five Russian wheat aphid biotypes have been identified in Colorado, and sexual reproduction is the most likely source of this variation. It has been suggested that Russian wheat aphid has specific requirements for winter conditions that might induce holocycly. Such conditions might be found at elevations higher than those of the main Colorado wheat production areas. The objectives of this study were to (1) identify host plants that Russian wheat aphid utilizes at higher elevations; (2) identify the elevations from 1500 to 3,000 meters above sea level at which aphids are most abundant; and (3) find sexual forms of Russian wheat aphid or other evidence of holocycly.