The relationship of temperature, moisture, and photoperiod was studied under laboratory conditions relative to termination of diapause inPectinophora gossypiella(Saunders). Field conditions occurring at Mesa, Arizona, for the midmonth periods of March, April, and May were simulated in environmental chambers, and diapausing larvae were subjected to these temperature conditions in both wet (contact moisture) and dry (ca. 50% RH) environments. Diapausing larvae were also subjected in constant-temperature cabinets to mean temperatures of the 3 monthly periods. Both studies indicated that conditions occurring during mid-April were most favorable for pupation and survival.Constant-temperature studies indicated that 13.9°C is below the threshold of development under both wet and dry conditions and that only under wet conditions is the 15.6°C temperature favorable. Temperatures of 17.8°C and 20.0°C were less favorable than 22.2°C under dry conditions for pupation and adult emergence, but little difference was noted between 20.0°C and 22.2°C under wet conditions, except for delayed pupation at the lower temperature.A limited study of photoperiod effects comparing a 14-h with a 10-h day indicated that a slightly higher rate of pupation occurs in the day-long regime. This was more evident under constant-temperature conditions than under fluctuating conditions.