We have developed an individual-based model describing the interactions of thousands of individuals of 19 species in a food web of plants, lepidopterans, and parasitoids from the Alaka`i Swamp, Kaua`i, Hawai`i. We have incorporated the behavior of individual insects, modified by experience, in the food-web model, which is based on thousands of interaction data compiled over the course of a three-year field study. The parasitoids are all alien to Hawai`i, and two of the three were intentionally introduced biocontrol agents. The simulation demonstrates that indirect effects on native species from alien species not directly interacting with those species should not be ignored when evaluating potential or realized non-target effects of biological control agents.