A phenological model of gypsy moth egg development is proposed that distinguishes three phases of egg development, prediapause, diapause and postdiapause. A technique of measuring respiration rates of individual eggs was developed and respiration rate was used as a physiological variable to distinguish the phases. The pattern of respiration rate provided strong evidence in support of three distinct developmental phases. Respiration rate developed embryos declined sharply as prediapause was entered and rose sharply when diapause was completed. When the effect of age on respiration rate was removed, temperature had a uniform effect on respiration rate throughout the egg stage. A 10°C decrease in temperature caused an approximate 0.4 fold decrease in respiration rate, indicating that eggs in diapause are as equally responsive to temperature as egg in a nondiapause phase. Developmental rate in prediapause was strongly temperature-dependent, and the relationship was described by a non-linear function. Prediapause duration was approximately 13 days at 31°C. The depletion of stored triglycerides was strongly linked to the completion of prediapause. Developmental rate in postdiapause was found to be temperature- and age-dependent. Developmental response to temperature was relatively weak and linear at the onset of postdiapause. As postdiapause advanced, the response became stronger and non-linear. The temperature- and age-dependent developmental response was fully described by the temperature-dependent developmental response at the onset of postdiapause, and by a temperature-dependent rate change parameter. / Ph. D.