Temperature-dependent developmental rate curves for larvae and pupae ofCotesia melanoscela(Ratzeberg), a parasitoid of the gypsy moth,Lymantria dispar(L,), were developed using linear and nonlinear models. There were small but statistically significant differences among developmental rates of parasitoids reared in first, second, and third host instars when the hosts fed on oak foliage. Differences in developmental rate between parasitoid larvae developing in first-instar hosts feeding on foliage versus artificial diet and between male versus female parasitoid pupae were more substantial. Although ther2values for the linear model were high, the deviations from regression were significant. Two nonlinear models fit well (highr2) for all treatments of parasitoid larvae and pupae, and the deviations from regression were not significant. Cumulative Weibull functions were fit to the data from all treatments to model the distribution of developmental time. Applications of these models are discussed.