The pine butterfly, Neophasia menapia Feld., has been at epidemic levels in the Bitterroot and Missoula valleys for the past 2 years (Ciesla et al. 1971) (Bousfield and Meyer 1972). Several reports of conspicuous pine butterfly flights on the Flathead Indian Reservation prompted an evaluation of the potential for pine butterfly defoliation in this area in 1973.