A computer simulation model of interactions between cotton plant fruiting, boll weevil densities and the parasitoid catolaccus grandis (Burks) was developed to simulate the effects of different release rates. The model predicted that sequential releases at weekly intervals are more effective in reducing boll weevil damage than single releases of similar magnitude. The model also predicted that weekly releases of C. grandis will be effective against boll weevil immigration rates of 1-10 adults per acre per day during the first 30-90 days. Another important prediction of the model is that increase of parasitoid emigration rates from the field has a significant effect on its ability to control boll weevils immigrating at rates of 50 adults/acre/day or greater. Releasing parasitoids twice a week in comparable numbers reduces the effect of parasitoid emigration.