The developmental times, survival rates and reproduction of the cotton aphid, Aphis gossypii Glover and the green peach aphid, Myzus persicae (Sulzer) were separately evaluated on detached pepper leaves at eight constant temperatures (15.0, 175, 20.0, 22.5, 25.0, 275, 30.0, and 32.5 degrees C) in temperature cabinets. Immature stages of A. gossypii developed significantly faster than those of M. persicae at temperatures of 20.0 and 22.5 degrees C, and 27.5 and 30.0 degrees C. The green peach aphid had a significantly shorter developmental period than the cotton aphid at 15.0 degrees C. Constant 32.5 degrees C was lethal to immature stages of M. persicae. The intrinsic rates of increase of A. gossypii were statistically higher than those of M. persicae at temperatures of 175 degrees C and above. It was evident that M. persicae performed better at cooler temperatures, having the capability to colonize pepper plants in greenhouses during winter and spring. As soon as average daily temperatures exceed 20.0 degrees C, the cotton aphid will outperform the green peach aphid and has a higher likelihood to colonize pepper plants quickly.