A synthetic pheromone of the western pine shoot borer, Eucosma sonomana Kearfott, has been used successfully as a 'mating disrupter in northern Idaho and western Montana since 1984. Infestation levels in treated ponderosa pine plantations declined from an average of 28 percent infested in 1983 to 5.5 percent by 1986. At the same time, infestation levels in the untreated check areas increased from an average of 24 percent to 30 percent from 1983 to 1986.