A temperature driven model based on field conditions was developed for determining the growth rates of populations of the green peach aphid (GPA),Myzus persieae(Sulzer), at high temperatures. At peak mid-summer temperatures, 2 thresholds were determined: (1) a decelerated phase of population growth (39°–46°C) and (2) a negative phase of population growth (>46°C). In 2 other runs, temperatures never reached the threshold of the phase of negative growth; however, the population growth decelerated at a lower threshold (31.6°–42.3°C) than in the mid-summer test.