Epidemic levels of the pine butterfly, Neophasia menapia (Felder and Felder) have been evident in ponderosa pine stands in the Bitter Root Valley since 1969. Evaluations of this infestation were initiated in 1970 to assess overwintering egg populations at 20 locations within the infestation (Ciesla et al. 1971). Defoliation was estimated following the feeding period in 1971 and a linear regression model was computed using defoliation as the dependent variable and egg density as the independent variable (Bousfield and Ciesla 1971). The purpose of this study was to provide a basis for predicting future population levels. The objective of this evaluation is to test the prediction model, forecast 1972 defoliation potential, and to obtain additional biological information on the infestation.