The biology of 3 known biotypes (A, B, and C) ofSchizaphis graminum(Rondani) was studied at various temperature gradients from 10.0° to 32.9°C In the laboratory. Host plants included greenbug-resistant and susceptible barleys and sorghums. The optimum temperature for reproduction as between 21.9 and 23.9°C. The minimum constant temperature at which reproduction occurred was 10.0°C; the maximum was 32.9°C. Resistance in sorghum increased as temperature increased. The fecundity of greenbugs was generally much lower on resistant than on susceptible plants. Biotype C was better adapted than A or B to either temperature extremes. At cycling temperatures the greenbugs were capable of recovering and reproducing at a much higher rate than at constant extreme temperatures.