a1 Forest Research Laboratory, Department of Fisheries and Forestry, Fredericton, New Brunswick
The heat requirements for diapause termination in pupae of Hyphantria cunea are subject to a high degree of generic control. Offspring–parent regression analysis based on a positively assortative mating pattern, which is the normal pattern in field populations of this species, provides a slope of 0.60. Positive skewness in the distribution of heat requirements can be reduced by conversion to logarithms. The inheritance of heat requirements is sex-linked, with the female being the heterogametic sex. Fitness characters that are significantly correlated with heat requirements affect larval and pupal survival rates and the weight of both male and female pupae. When the effects of these correlated survival rates are removed mathematically, the slope of the offspring–parent regression is increased to 0.80.Changes in the heat requirements of natural populations, in relation to the amount of heat available each year, influence their survival rates. The comparison of actual and calculated changes, based on models for heritability and selection pressures, will be the subject of a later paper in this series on H. cunea.
(Received September 26 1969)