The effect of photoperiod, temperature, and humidity on oviposition and egg development was determined to optimize laboratory rearing ofNeodiprion fulvicepsCresson on cut branches of ponderosa pine (Pinus ponderosaDougl. ex Laws). The maximum number of eggs laid and eggs hatched occurred at 15°C. No oviposition occurred at 4°C. Egg development time was too slow to be practical at 10°C; no eggs hatched after 75 d. No differences in number of eggs laid occurred at 30, 40, and 50% RH; however, number of eggs laid was significantly lower at 60%. The maximum number of eggs hatched and the shortest egg development time occurred at 50% RH. Photoperiod had no effect except on the percentage of hatch, which was greatest under short-day conditions. Egg incubation times were slightly shorter on seedlings than on mature cuttings.