The apple aphid was reared on 1-year-old trees in a controlled environment cabinet with simulated mid-June through October 1968 daylengths and temperatures. Maximum rates of increase (ca. 2.7-fold per week) were observed during the first 5 weeks of the experiment and maximum populations were obtained in 7 weeks at the time the trees stopped growth when the diel photoperiod was 14.8 hr, and light/dark temperature was 20.5°/15.5 °C. The ratio of nymphs to adults increased from 5:1 to 10:1 from week 2 to week 8, followed by a rapid decline. At week 12 there were more adults than nymphs and the nymph:adult ratio remained 1:3 through the remainder of the experiment. Alate aphids appeared 2 weeks following infestation, increased very rapidly, ca. 6-fold per week, and maximum abundance was noted at the end of 6 weeks. Their numbers declined nearly as rapidly at ca. 0.35-fold per week and they were not seen after week 11. As the numbers of alate aphids decreased, apterous adults increased to week 12, remained constant to week 15, and slowly decreased in an environment of shorter daylengths and lower temperatures. The rate of apterous adult aphid increase was similar to the rate of accumulated degree days during the first 8 weeks and again in the 10- to 15-week period.Aphids were concentrated on the tree tops during the first 6 weeks of the experiment. A gradual migration followed and the aphids became dispersed over the trees with minor concentrations near the centers of the trees.