Survival, growth, and behavior of Helicoverpa zea (Boddie) and Heliothis virescens (F.) (Lepidoptera: Noctuidae) on genetically engineered cotton expressing the Vip3A insecticidal protein

Abstract

Larval behavior, survivorship, and injury potential of Helicoverpa zea (Boddie), and tobacco budworm, Heliothis virescens (F.), was evaluated on cotton plants genetically engineered to express Bacillus thuringiensis (Bt) insecticidal proteins, Vip3A and Vip3A +Cry 1Ab (VipCot™). Larvae (2-d-old) of both species were infested on plant terminals of vegetative or flowering stage cotton plants. Regardless of species, more larvae migrated from the plant terminals of Vip3A and VipCot plants compared to larvae infested on a conventional non-Bt cotton line (Coker 312). Larval (2-d-old) survivorship on VipCot™ plant structures was generally lower than that on similar structures of the Vip3A cotton line. However, H. virescens survivorship was higher than that for H. zea on similar structures of Vip3A plant. Age-specific (2 d, 4 d, 6 d, and 8 d-old larvae) survivorship was further evaluated on flower buds (cotton squares) of Vip3A and VipCot™ plants. Cumulative survivorship levels for both species and all larval ages were significantly lower on Vip3A and VipCot™ squares compared to that for Coker 312. No larvae of either species successfully pupated on VipCot™ squares. A limited number of H. virescens larvae completed larval development on Vip3A cotton squares. Field trials quantified cotton fruiting form injury on these Bt lines from artificial and native infestations of H. zea or H. virescens. Larvae (L2 stage) of H. zea infested in white flowers injured an average of 8.6, 4.6, and 1.0 fruiting forms per larva on Coker 312, Vip3A, and VipCot™ plants, respectively. Similarly, H. virescens injured an average of 9.2, 5.9, and 0.9 fruiting forms/larva on Coker 312, Vip3A, and VipCot™ plants, respectively. Native infestations of both species during 2005-2007 injured fewer fruiting forms on the Bt lines compared to that on Coker 312 plants. Seasonal efficacy patterns showed the VipCot™ plants to be more durable with less fruiting form injury than that recorded on Coker 312 and Vip3A, especially during periods of peak insect infestations. The combination of two proteins in the VipCot™ line generally improved efficacy against these pests compared to that of the single protein in the Vip3A line.