Ecological genetics is the study of genetic changes and how these are influenced by the biological parameters of a species. One genetic change of importance to the cotton Industry Is the evolution of Insecticide resistance in Heliothls armigera. Biological parameters which are thought to determine the rate of evolution of resistance and its spread throughout the cropping areas Include population size, migration, the species' ability to overwinter in cropping areas, the frequency of egg-lays and the abundance of non-cotton hosts. The results of these studies are of more than just theoretical interest; they have led to a number of recommendations about pest control. This paper will summarise a number of studies relevant to the ecological genetics of H. armigera and H. punctigera.