THE EFFECTS OF PHOTOPERIOD AND EFFECTIVE TEMPERATURES ON THE SEASONAL PHENOLOGY OF THE CODLING MOTH (LEPIDOPTERA: TORTRICIDAE)

Abstract

The photoperiodic reaction in North American codling moth populations displayed clinal-type variation similar to populations in Europe. A latitudinal shift of 10° to the north corresponded to an increase of 1.25 h in the critical photoperiod. Intrapopulation variance in diapause response appeared to be similar in populations of different origin. The critical photoperiod was not constant for a geographic population but varied between years probably due to the modifying effect of prediapause temperatures. In Michigan and other areas in the northeastern United States with similar climate the codling moth is essentially bivoltine with considerable yearly variability in second generation emergence. A graphic model is presented which gives an estimate of voltinism and the proportion of diapausing first-generation larvae based on the seasonal heat unit total at the time of diapause initiation. From an analysis of original data and historical phenological records an algorithm was developed which describes the relationship between effective temperatures and the variance of second generation emergence and which can predict population curves for climatically different years. Use of this predictive method in conjunction with monitoring information provided by a pheromone trap is discussed.