A computer model of the interaction between the fungal pathogen Entomophaga maimaiga Humber, Shimazu & Soper and its host, the gypsy moth, Lymantria dispar (L.), had previously been developed to simulate infection by fungus resting spores (azygospores) that are present in soil and germinate in spring if moisture is adequate. This model is now expanded to include infection caused by conidia that are produced on dead, infected caterpillars when relative humidity is near 100%. As inputs, the model uses temperature, relative humidity, rainfall, abundance of resting spores in the soil, and gypsy moth population density. From plots in 1999, 2000, and 2001, data on weather conditions (the first year from daily weather station data and the last two from in-plot data loggers) were obtained, and gypsy moth density and resting spore abundance were determined. Also, collections of gypsy moth larvae were taken weekly to determine proportion of infection by the fungus. These data were used to find best-fitting parameters for the model. Using the same parameter values, model output was close to data for all years. When conidial dispersal was incorporated in the model, output and data were even closer. A validated model should be useful for evaluating and predicting gypsy moth-fungus interactions in forests.