Economic comparisons of insect pest management strategies were made for the heliothine pests, bollworm, Helicoverpa zea (Boddie), and tobacco budworm, Heliothis virescens (F.); under 18 different combinations of in-season rainfall, pest densities, insecticide use, insect resistant cotton, and densities of beneficials insects. Comparisons were made using a mechanistic simulation model of insect-plant interactions. The model, referred to as the Integrated Crop Ecosystem Management Model (ICEMM), combined modified versions of the insect model, TEXCIM 5.0, and the cotton plant model, GOSSYM. Economic returns were calculated for each management strategy under each combination of in-season rainfall condition and heliothine density. In-season rainfall conditions were categorized as dry, average, optimum, and wet. Tobacco budworm densities were none, low, medium, and high. Management strategies were: no insect management when heliothines were absent; no insect management when heliothines were present; no insect management when heliothines were present with a light or heavy density of beneficial insects; one insecticide application at a low or high rate when heliothines were present; one insecticide application at a low or high rate when heliothines were present with a light or heavy density of beneficials; transgenic cotton expressing a Cry1A gene encoding an insecticidal delta-endotoxin from Bacillus thuringiensis var. kurstaki, (Bt cotton), with no pest management; Bt cotton with a light or heavy density of beneficials; and Bt cotton with one application of insecticide at a low or high rate. The greatest net returns were obtained when heliothines were absent and insect management was not employed. When heliothines were present, the management strategy with doing nothing plus heavy beneficials resulted in the highest net returns. Optimum rain fall also improved net returns compared to other in-season rainfall rates.