VARIATION IN SPRING EMERGENCE PATTERNS AMONG WESTERN CHORISTONEURA SPP. (LEPIDOPTERA: TORTRICIDAE) POPULATIONS IN SOUTHERN OREGON

Abstract

AbstractAn analysis of the times to emergence in three sparse populations of Choristoneura spp. in western North America indicates that there was considerable variation in the calculated threshold of development among populations. Also, the number of heat units required to effect the emergence of any specified proportion of the population varied considerably among populations. The pattern of intra-population variation in times to emergence is such that the within-family variation was much larger than the among-family variation in the two populations from areas in which white fir is the only host. In the other population, from an area with a mixed stand of Douglas-fir and white fir, the pattern is reversed. This pattern remains even after an accounting is made for the parental host and larval color morph. It is hypothesized that the pattern of variation in the times to emergence may be due to the presence, in the latter population, of physiological morphs which cannot be recognized either by their appearance or their host of origin. These results have clear implications for pest management procedures which attempt to schedule activities related to the emergence of these insects in the spring.