We examined the development and reproduction of individual Russian wheat aphids, Diuraphis noxia, that developed either in solitude on their own wheat plant, or in a group of ten conspecifics. We examined two different biotypes of D. noxia feeding on three different wheat cultivars at two constant temperatures. Survival to maturity was higher among grouped aphids than among solitary aphids, especially on cultivars susceptible to a particular biotype. Individuals in groups developed faster than solitary individuals on cultivars susceptible to a particular biotype, but not on those expressing resistance to it. There was a significant temperature-biotype interaction; the developmental benefits for group-feeding in biotype 2 aphids appeared greater at the higher temperature (24° C) than at the lower (20° C). Similar results were obtained in an experiment assessing reproductive performance. Advantages for group-feeding aphids (enhanced reproductive rates) were most pronounced when they fed on cultivars susceptible to that particular biotype, and more pronounced for biotype 2 at 24° C than at 20° C. The results indicate that D. noxia individuals develop and reproduce faster as colonies grow, effects that appear to be a function of physiological changes in the host plant that are induced more effectively by groups of aphids than by solitary individuals. These group-feeding effects, mediated by the host plant, interacted with both temperature and cultivar in a biotype-specific manner. Implications are discussed for life tables that assume fixed rates of aphid development and reproduction extrapolated from measurements of solitary individuals.