Mountain pine beetle activity has increased from about 350 infested trees in 1972 to over 1,200 infested trees in 1974 on the Bitterroot National Forest. The majority of infestation occurs in second-growth, overstocked, ponderosa pine stands in the West Fork Bitterroot drainage. An increase in number of trees killed is expected in 1975. Commercial thinning is encouraged to remove infested trees and improve stand vigor to reduce the infestation to endemic levels.