Abstract
AbstractThe seasonal distributions of Choristoneura occidentalis Freeman and C. retiniana (Walsingham) males attracted to pheromone sources overlapped considerably at two sites in south-central Oregon. Bimodality in the seasonal distributions of trapped males of both species was associated with a period of cool weather. The daily periods of female calling, and attraction of males to female-baited traps and to chemically baited traps overlapped greatly between the two species. However, these three aspects of C. occidentalis mating behavior began 1–2 h before those of C. retiniana. Under laboratory conditions, there was also considerable overlap in the calling periods of the two species; but again, C. occidentalis females initiated calling slightly earlier than did female C. retiniana. Females of both species continued to call many hours past the cessation of male attraction to pheromones in the field. Male attraction to pheromones occurred earlier on cool evenings than on warm evenings. Laboratory studies indicated a similar effect of temperature on timing of female calling. Little intraspecific variation in calling periodicity was observed among field-collected populations of each species. However, a C. occidentalis laboratory colony appeared to have partially lost its circadian rhythm of calling.
Published Version
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