When low (day mean, 27.0°C; range, 6.8–42.0°C), medium (day mean, 28.0°C; range, 7.2–42.4°C), and high (day mean, 32.3°C, range, 7.3–46.4°C) temperatures were produced in field cages by covering the cages 0, 80, or 98%, respectively, with clear plastic sheets placed over the Saran cloth, the population growth rates of green peach aphids (GPA),Myzus persicae(Sulzer), decreased with increasing temperatures whereas accumulated degree-hours above 0°C increased with temperature. Thus, heat units accumulated at high temperatures are not strictly equivalent to those accumulated at lower temperatures when one is calculating population growth rates. Accordingly, a model was constructed to calculate the effective growth units that contribute to population growth of the GPA. The calculations are based on a second-order curve whereby rates of increase of the green peach aphid were compared with temperature by using data taken at intervals of 5°C. The distribution provided a weighting function that specifies the relative contributions of growth units to population growth at different temperatures.