Sex Pheromones and Behavioral Biology of the Coniferophagous Choristoneura

Members of the coniferophagous Choristoneura genus can be found in all conifer-forested regions of North America. The distribution of its species is reasonably well established and most members of the group are taxonomically distinct. There has been one recorded case of natural hybridization between C. occidentalis and C. retiniana (68). In areas of sympatry among other species, the mechanisms of reproductive isolation are not well understood and little data is available to assume lack of hybridization. Pheromone differences may, in fact, be an important factor in species isolation (24). The two most economically important and widely distributed species, C. fumiferana, the spruce budworm, and C. occidentalis, the western spruce budworm, are believed to be geographically isolated and are the most in­ tensively studied of all the budworms. Spruce budworm, the most extensive in range of all the bud worms , exhibits population oscillations (35, 49 ) of very large amplitudes, with periods of extremely high densities when defoliation and tree mortality can occur (42) over extensive areas. Several reviews have summarized the biology (56) and the sex-pheromone chemistry (59, 60) of the coniferophagous Choristoneura. The pheromone­ mediated behavior of both C. fumiferana (3, 60) and C. occidentalis (2; J. Sweeney & J. McLean, unpublished data) has been studied in some detail, and this research may help decode the communication systems in the other