The level of cross-resistance between the Bacillus thuringiensis toxins Cry1Ac and Vip3A was determined using one susceptible and three Cry1Ac-resistant strains of tobacco budworm, Heliothis virescens. Concentration-mortality data confirmed that the three Cry1Ac-resistant tobacco budworm strains, YHD2, KCBhyb, and CXC, were at least 52- to 424-fold resistant to Cry1Ac compared to the susceptible strain, YDK. Concentration-mortality test results using Vip3A indicated that mortality was similar among all four tobacco budworm strains. Relative larval growth on Vip3A was highly variable at concentrations at or lower than 25 mg/ml but was more consistent on higher Vip3A concentrations. Relative larval growth on Cry1Ac reflected concentration-mortality test results, as YHD2 larval growth was unaffected by the tested concentrations of Cry1Ac. KCBhyb and CXC LC50s and growth ratios verified a more moderate level of Cry1Ac resistance compared to YHD2. Differences in larval growth were much more pronounced on Cry1Ac than on Vip3A. Results of these experiments demonstrate that cross-resistance is non-existent between Cry1Ac and Vip3A in tobacco budworm. Thus, the introduction of VipCot lines could delay Cry1Ac-resistance evolution in tobacco budworm, thus increasing the sustainability of current technologies.