Abstract
Annual changes in genetic quality were measured in natural populations of Hyphantria cunea Drury for 12 years in New Brunswick and Nova Scotia. Models for heritability and natural selection pressure, derived independently from experimental data, are used to simulate the changes in quality over the same period. In seven of eight areas, observed and simulated trends are significantly correlated. Regressions between observed and calculated values, examined with respect to both means and slopes, suggest how these preliminary models may be refined. The influence of genetic changes on the natural regulation of population density is discussed briefly, but analysis is deferred to a later paper in this series on H. cunea.