Days to adult emergence of overwintering apple blotch leafminers,Phyllonorycter crataegella(Clemens), and one of its primary parasitoids,Sympiesis marylandensisGirault, are presented for a series of six constant temperatures between 4 and 30°C. Models for the distributed development based upon the means of individual development rates and their associated variances were constructed and validated with field data from Massachusetts. The difference in emergence between apple blotch leafminer adults and female parasitoid adults is depicted by computer mapping of a “biological window.”