Embryogenesis, embryo survival, and hatching were studied in eggs of the red turnip beetle, Entomoscelis americana Brown, incubated at 9 constant temperatures (5–35 °C) for 5–50 days before cold storage at −5 °C for 200 days during winter. Embryogenesis occurred at all temperatures tested, but the threshold and upper limit for embryogenesis were near 5 and 35 °C, respectively, and the optimum-temperature range was about 12.5–20 °C. Embryo survival was about 12–65% lower in eggs incubated at 5 °C for 50 days and at 7.5 and 10 °C for 30–50 days than in those incubated at these temperatures for shorter times, indicating that prolonged exposure to temperatures near the threshold during embryogenesis adversely affects the embryos. Embryo survival declined to low levels in eggs incubated at 25 and 30 °C for more than 30 and 5 days, respectively, and only a small number of embryos survived in those incubated at 35 °C for 5 days. The times to 50% hatch in eggs that contained late-stage embryos before cold storage and had been incubated at 25, 30, and 35 °C were 1.6, 2.6, and 6.5 times longer, respectively, than in those at 12.5–20 °C. These results indicate that embryos incubated at 25–35 °C during embryogenesis before diapause require a recovery period before initiating the normal postdiapause events, and that these events can be adversely affected by unfavorably high temperatures before diapause. The physiological and ecological significance of the data is discussed.