A series of field trials from 2005 to 2007 evaluated the performance of transgenic cotton lines expressing the Vip3A protein against native and artificial infestations of bollworm, Helicoverpa zea (Boddie), and tobacco budworm, Heliothis virescens (F.). Two Bacillus thuringiensis Berliner (Bt) cotton lines expressing either a single protein (Vip3A) or a combination of proteins (Vip3A + Cry1Ab [VipCot™]) were sampled throughout the production seasons and scored for fruiting form injury and larval survivorship. A conventional non-Bt cotton cultivar, Coker 312, was included as a negative control. Species composition and native infestation levels varied both within and across years, but Bt cotton lines had significantly fewer damaged fruiting forms and surviving larvae compared to control plants. VipCotplants had fewer damaged fruiting forms and fruiting forms infested with larvae compared to that on Vip3A plants. Seasonal patterns of efficacy generally showed VipCotplants were more durable with fewer injured fruiting forms than that recorded on Coker 312 and Vip3A, especially during peak periods of heliothine infestations. Coker 312, Vip3A, and VipCot plants artificially infested with either H. zea or H. virescens larvae were visually inspected 3 d after infestation and every 2 d thereafter until larvae were no longer detected. Fewer damaged fruiting forms and larval survivors (both species) were recorded on Vip3A and VipCot plants than on Coker 312 plants. A single H. zea larva injured an average of 8.6, 4.6, and 1.0 fruiting forms on Coker 312, Vip3A, and VipCotplants,respectively. A single H. virescens larva injured an average of 9.2, 5.9, and 0.9 fruiting forms on Coker 312, Vip3A, and VipCotplants, respectively. The combination of two insecticidal proteins expressed in the VipCotcotton line demonstrated greater efficacy against a complex of heliothines than the single protein in the Vip3A line.