A population model of the codling moth,Laspeyresia pomonella(L.), is presented which simulates population behavior over several years. Derivation of the theoretical and biological structure of this model is discussed on a state by state basis. Each transition equation is developed around a central framework which separates density-dependent and -independent effects. These equations are then fitted to observed data.The transition equations are assembled into a computer program, CODMOTH. Output from this program shows acceptable agreement with observed data from field and laboratory, indicating that the model can adequately simulate population behavior for at least 5 yr.Model sensitivity to equation parameters and program constants is examined to determine the allowable error for these values. Model output varies by only 10% if a parameter is changed by an avg of 45%.The significance of the density-dependence component of each equation is examined. Feedback processes are found to be most important in the fecundity and 1st-instar survival equations. Sex ratio and voltinism are least affected while larval survival within the apple and survival to cocooning sites are intermediately affected.