Studies were carried out to show the effect of rearing regimes combined with three different temperatures on the rate of development of Agrotis ipsilon. Data obtained from these experiments revealed that the degree days required for the immature stages differed according to temperature or type of food, which were 208.4, 228.5, 229.1 and 267.5 at 22°C, 27°C, 30°C and 35°C when larvae were fed on castor oil bean leaves and it was 176.3, 226.05, 226.5 and 272.7 at the previ­ous temperatures when larvae were fed on clover (berseem) leaves. Also, the median developmental rate was between 0.019 to 0.03 at the same temperatures, but results showed that the rate of development at the lower temperature when fed on berseem leaves was higher com­pared with those fed on castor oil bean leaves according to the differ­ent contents of the two regimes.