Developmental rate, mature weight, number of eyed embryos, and size of the largest embryo of apple aphids,Aphis pomi(De Geer), reared at constant temperatures, were nonlinear functions of temperature, with gradual decline phases above optima that occurred at relatively moderate temperatures. Rearing experiments using paired combinations of high, moderate, and low temperatures demonstrated departures from expected values for these bionomic parameters, calculated by extrapolating results of single temperature rearings. These results suggest unequal responses to temperature by different developmental stages, residual effects, or both, including delayed acclimation and apparent non-reversible injury. Development, weight, and ovarian parameters of fundatrices, oviparae, and males are compared with those of viviparous apterae.