A conceptual model is formulated which describes overwinter developmental rate for Heliothis zea (Boddie) pupae. An analytic function for prediction of spring emergence as a function of temperature is developed through the technique of matched asymptotic expansions. The resultant model is fit to observed post-diapause developmental rates measured at various constant temperature regimes. From these data, parameters were estimated for 10, 50, and 90 percentile emergence. A field spring emergence model is presented which includes the temporal variation in post-diapause morphogenetic development, the spatial distribution of overwintering pupae in the soil, and the spatial/temporal distribution of soil temperature. Model results are compared to an observed field emergence.