Oviposition and egg hatchability of once-mated, nondiapauseHypera postica(Gyllenhal) were studied for 35 weeks under constant temperatures (10, 23, and 30°C) and alternating temperatures (4.5 and 15.5°C each 12 hours). Maximum oviposition (1788 eggs per female) occurred at alternating temperatures (4.5–15.5°C). Oviposition at 10 and 23°C, though not significantly different from each other, was significantly less than oviposition at 4.5–15.5°C. A temperature of 30°C was unfavorable for oviposition.The maximum number (1022 eggs per female) and percent (90%) of viable eggs occurred at 23°C, indicating that an intermediate temperature was optimal for fertilization. Egg hatchability at 4.5–15.5°C was reduced to 36% because 4.5° apparently disrupted sperm activity and because sperm were depleted in late oviposition. Egg hatchability at 10°C also was reduced (32 % ). Egg hatchability at 30°C was reduced to 0 after 4 weeks. Females which had been at 30°C laid viable eggs when they were remated after 8 weeks and held at 23°C.