Effects of Temperature and Photoperiod on Voltinism of Geographical Populations of the European Corn Borer, Pyrausta nubilalis1

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Abstract
A study was wade of the effects of temperature and photo period on the developmental patterns of European corn borer population samples from northern Wisconsin, southern Wisconsin, southern Minnesota, Iowa, southern Ontario, Massachusetts, Nebraska, northern Kansas, Pennsylvania, and southeastern Missouri. Under a series of standard laboratory conditions of temperature and photo period, the incidence of diapause and rate of larval growth differed significantly among the several populations. The incidence of diapause was positively correlated with the latitude of the population source. The characteristics of the temperature and photo periodic responses differed among the populations, indicating complex evolutionary trends. The populations differed not only in the effect of temperature and photo period on the incidence of diapause, but also in the effect of temperature on larval growth rates. The importance of these population differences in the voltinism manifested under field conditions is discussed. An empirical basis for predicting summer pupation of the borer in southern Wisconsin was developed, employing seasonal temperature accumulation up to a day length of 14.75 hours (July 25, at 43° N.).