Eclosion of overwintering eggs of pine needle scale,Chionaspis pinifoliae(Fitch), was modeled from growth chamber fluctuating temperature rearings. A computer model, DEGDAY, was used to determine daily and accumulated degree-day accumulations to hatch. This model and simple regression techniques were used to identify the developmental threshold. Percentage of survivorship ranged from 0 at 9°C to 98 at 18.5°C. At 18.5°C, 136 degree-days accumulated to hatch, and time to 50% hatch was 17.25d. The developmental threshold lies between 10.8 and 11. 8°C.