The larch casebearer, Coleophora laricella (Hubner) was first reported attacking western larch, Larix occidentalis, in Idaho in 1957 (Denton, 1958), 71 years after its introduction into Massachusetts from Europe. The apparent successful regulation of this insect in the eastern U.S. by introduced parasites prompted biological control attempts in the West. Introduction of Agathis pumila (Ratzeburg), considered one of the most significant parasites in the East, was emphasized following a period of laboratory and field evaluations. Between 1966 and 1969, Forest Insect & Disease Management released A. pumila at 378 locations in Washington, Idaho, and Montana. Most releases consisted of attaching parasitized casebearer-infested branches to lower branches of three infested trees at each release location. Evaluations made between 1967 and 1972 verified the presence of A. pumila on 127 plots out of 270 examined and percent parasitism ranged from 0.1 to 90 percent.