Lethal and sublethal effects of cotton expressing single and pyramided proteins of Bacillus thuringiensis (Bt) on Helicoverpa armigera (Lepidoptera: Noctuidae), Spodoptera litura (Lepidoptera: Noctuidae), and Spodoptera frugiperda (Lepidoptera: Noctuidae).

The susceptibility to proteins from Bacillus thuringiensis (Bt) can vary among lepidopteran pest species. While Bollgard 3 cotton (BG3) effectively controls the primary pest Helicoverpa armigera (Hübner) in Australia, its effectiveness against other pests, such as Spodoptera litura (Fabricius) and Spodoptera frugiperda (J. E. Smith), is unknown. This laboratory study assessed the survival and development of H. armigera, S. litura, and S. frugiperda larvae when fed foliage from a non-transgenic cotton variety (CC) and 3 transgenic cotton varieties: Bollgard (BG1) expressing Cry1Ac, Bollgard II (BG2) expressing Cry1Ac and Cry2Ab, and Bollgard 3 (BG3) expressing Cry1Ac, Cry2Ab, and Vip3A. Pyramided Bt cotton had greater negative effects on survival and development of all species compared with CC or BG1. The proportion of H. armigera that eclosed as adults was very low when larvae fed on BG2 or BG3 compared with BG1. Eclosion rates of S. litura and S. frugiperda on BG3 were much lower compared with BG2 and BG1. This study demonstrates that BG3 has greater efficacy against a wider lepidopteran pest complex compared with previous Bt cotton products. Despite efficacy in the laboratory, S. litura larvae are reported to be surviving in BG3 fields, suggesting other factors are influencing field efficacy. As BG3 production expands across tropical northern Australia, preserving the susceptibility of S. litura and S. frugiperda to BG3 proteins is crucial. This study identifies the need for further research on field survival and resistance management strategies for secondary pest species.