Taylor's power law, Iwao's patchiness regression, and the negative binomial distribution with a common value ofkwere used to model variance/mean relationships of populations of four species of cereal aphids,Schizaphis graminum(Rondani),Macrosiphum avenae(F),Rhopalosiphum padi(L.), andRhopalosiphum maidis(Fitch), occurring in winter wheat and spring oat fields in South Dakota. Taylor's power law generally provided a better model of variance/mean relationships than did the other models. Intercepts of Taylor's power law regressions (loga) varied among populations of some cereal aphid species occurring on different host crops. Regression slopes (b) generally did not differ among populations inhabiting different crops; however,bdid differ among populations ofR. padisampled from spring oats and winter wheat. Power-law parameters were independent of field and year at which populations were sampled and time during the growing season at which samples were taken. These results suggest that marked changes in environment (e.g., different host crops) influenced spatial distributions of cereal aphid populations and, hence, the value of power-law parameters. However, for populations inhabiting either host crop, power-law parameters seemed to be independent of temporal and spatial variation.