Age-Specific Mortality of Helicoverpa zea and Heliothis virescens (Lepidoptera: Noctuidae) Larvae on Flower Buds of Transgenic Cotton Expressing Vip3A and VipCot™ Insecticidal Proteins

Abstract

The age-specific mortality of bollworm, Helicoverpa zea (Boddie), and tobacco budworm, Heliothis virescens (F.), larvae was quantified on flower buds (squares) of transgenic Bacillus thuringiensis (Bt) cotton expressing Vip3A and VipCot™ (Vip3A + CrylAb) proteins. Cumulative mortality levels for both species and all larval ages (2 d, 4 d, 6 d, and 8-d-old) were significantly higher on squares of the Vip3A and VipCot cotton lines compared with that for the nonBt Coker 312 cotton. In general, H. zea and H. virescens larvae demonstrated significantly lower survival on VipCot squares compared with larvae that were offered Vip3A squares. The final cumulative mortality levels of H. zea larvae occurred more rapidly than that observed for H. virescens larvae on Vip3A squares. On Vip3A squares, the rates of peak mortality were similar among H. zea age-classes. Heliothis virescens in 4, 6 and 8-d-old age-classes survived longer than 2-d-old larvae on Vip3A squares. However, on VipCot squares, 8-d-old larvae of both species survived longer compared with other age-classes. Regardless of age-class, no larvae of either species were capable of completing pupation on squares from the VipCot cotton line. The combination of two insecticidal proteins expressed in the VipCot cotton line improved heliothine efficacy levels above that of the single protein in the Vip3A line and should exceed the requirements of the cotton industry for registration and regulation of transgenic Bt cottons. This level of VipCot toxicity to both target species supports continued development of the technology to provide another useful transgenic tool with considerable IPM and IRM value.