PROC. ENTOMOL. SOC. WASH. 86(2), 1984. pp. 439-442 THE DISTRIBUTION OF THE WESTERN BUDWORM, CHORISTONEURA OCCIDENTALIS FREEMAN (LEPIDOPTERA: TORTRICIDAE), IN WYOMING' Michael G. Pogue and Robert J. Lavigne (MGP) Department of Entomology, Fisheries, and Wildlife, 2 1 9 Hodson Hall, University of Minnesota, St. Paul, Minnesota 55108; (RJL) Entomology Section, Plant Science Division, University of Wyoming, P.O. Box 3354, University Sta-tion, Laramie, Wyoming 82071. Abstract. — Choristoneura occidentalis Freeman distribution in Wyoming, based largely on ultraviolet light trap data, is presented. Additionally, larval and pupal collections were made on the major host, Douglas fir, Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco. Choristoneura occidentalis Freeman is a widely distributed western polychro-matic species, difficult to distinguish other than by genital dissection. Until 1967, C. occidentalis was considered to be a western form of the spruce budworm, Choristoneura fumiferana (Clemens) (Freeman, 1967). Consequently, it is sur-prising that, although the species is recorded from southern British Columbia to northern New Mexico, no published records exist for Wyoming (Freeman, 1967; Stehr, 1967; Powell, 1980). The purpose of this paper is to fill in this distribution gap. Additionally, by establishing a long series in the University of Wyoming insect collection, taxonomists will have access to material should the necessity arise for the naming of additional species based on subsequent physiological and genetic studies. Like the spruce budworm, C. occidentalis exhibits periodic population explo-sions, which are detrimental to both lumber and recreation industries. Unpub-lished records for Wyoming suggest that these outbreaks are infrequent, although once initiated they may be widespread and extend over several years. McKnight (1967) mentions an outbreak that terminated in 1936 in Cody Canyon, Shoshone National Forest, Park County. Other population explosions occurred in the Front Range forests of Colorado in 1958 and 1959. These outbreaks were widespread in susceptible stands in Colorado and had extended into northcentral Wyoming in the Big Horn and Shoshone National Forests by 1962 (McKnight, 1967). The Missoula Forest Insect Laboratory reported an infestation in Yellowstone National Park in 1952 which, when discovered, extended over 2000 acres. By 1956, the infestation had spread to 142,500 acres of Douglas fir (Johnson, 1957). ' Published with the approval of the Director, Wyoming Agricultural Experiment Station, as Journal Article No. JA-11 08.