The development time of different stages of Sesamia nonagrioides Léfèvbre was studied in the laboratory at constant temperatures in the range 10–36°C. The relationship between the developmental rate (1/d) and the temperature (°C) was determined using both linear and nonlinear (Logan type III) models. The fit of the linear regression in the temperature range 15–27.5°C and Logan type III equation was good (R² > 0.97). The lower developmental threshold, calculated using the linear model, was t_b = 12°C. The nonlinear model gave a higher threshold of T_max = 36°C, and an optimal developmental temperature of T_rmax = 30°C. The flights of S. nonagrioides were studied in Lleida, Spain, from 1984 to 1997, and the number of degree-days required for their occurrence was calculated. A relationship between the degree-days required for the first flight calculated by the averaging method and the degree-days required for estimated diapause termination was obtained (R² = 0.84). This relationship allowed the prediction of the first flight occurrence in the field. The degree-days required for the second and third generations were then calculated as 730 and 491, respectively.