Before the advent of synthetic organic insecticides, it was much more difficult to control the codling moth, Carpocapsa pomonella (L.), in arid, hot areas with a long growing season, as in the Pacific northwest, than in cooler areas such as Ontario, where there is more rainfall and usually a shorter growing season. As a rule, in all apple growing areas, the codling moth is most numerous during summers in which the temperatures are above normal, particularly if the prevailing temperatures are high at dusk, when the moth is ovipositing. Consequently, unsatisfactory control in hot, dry areas, such as the South Okanagan of British Columbia, was attributed largely to the direct and favorable influence of climate on codling moth development (Webster, 1936).