The HEAPS (HE.licoverpa d.rmigera and l!.imctigera Simulation) model embodies all of our current knowledge on the ecology of Helicoverpa within cotton cropping regions. It differs from other models of Helicoverpa population dynamics in two main ways. Firstly it operates over an explicitly defined spatial representation of the agricultural landscape within the region being simulated, and secondly it simulates multiple sub-populations of Helicoverpa, each of which have their own demography and resistance gene frequencies. By necessity the model is a simplification of the real world, and there are many underlying assumptions governing its predictions. The HEAPS model is still in the process of being validated on a regional scale, and therefore the accuracy and precision of its predictions remain to be proven. However the model has already been a useful research tool for studying a range of issues relating to the regional population ecology of Helicoverpa. It is in this regard that we outline the use of the model to simulate the demographic and genetic response of H. armigera populations to IRM strategies (see Tabashnik, 1990)