A FORTRAN-based simulation model quantifying the interaction ofColeomegilla maculata(DeGeer) (Coleoptera: Coccinellidae) with green peach aphid (GPA),Myzus persicae(Sulzer)(Homoptera: Aphididae), populations on potato plants was developed. The model consisted of a GPA population, which was assumed to grow exponentially with time (h). Feeding ofC. maculataadults and larvae was included. TheC. maculatapopulation was assumed to be composed of eggs, larvae, pupae, prereproductive and reproductive adults. Natural mortality ofC. maculataeggs, larvae, and pupae was included, andC. maculataadults were assumed to die of old age after 1975 h. Cannibalism ofC. maculataeggs, larvae, and pupae byC. maculatalarvae was also included, as was a minimum number of GPA required forC. maculatato oviposit. The model satisfactorily described the change in GPA, and larval and adultC. maculatapopulations with time when tested against a 1977 data set. Model simulations indicated that temperature can greatly affect the predator-prey population dynamics.