Managing Spodoptera Species (Lepidoptera: Noctuidae) Found in Brazilian Soybean Fields with Bt Soybean and Insecticides

Abstract

Genetically modified (GM) soybeans expressing Cry1A.105/Cry2Ab2/Cry1Ac (event MON 87701 × MON 89788 × MON 87751 × MON 87708) and Cry1Ac (event MON 87701 × MON 89788) from Bacillus thuringiensis Berliner (Bt) are valuable technologies for managing key lepidopteran pests of soybean in South America, but do not provide stand-alone protection against Spodoptera species. Here, we evaluated the use of these Bt soybeans and their integration with insecticides for managing Spodoptera species. Cry1A.105/Cry2Ab2/Cry1Ac soybean provided reasonable levels of protection against S. cosmioides, S. albula, and S. eridania. However, S. frugiperda had higher survival on this Bt soybean, and Cry1Ac soybean showed low lethality against all species evaluated. Spodoptera larvae that survived on Bt and non-Bt soybean showed comparable susceptibility to flubendiamide and thiodicarb in diet-overlay bioassays. Regardless of soybean plant type, the field doses of flubendiamide and thiodicarb were effective in controlling surviving Spodoptera larvae. We conclude that Cry1A.105/Cry2Ab2/Cry1Ac soybean is effective in controlling S. cosmioides and S. albula, and also has reasonable control of S. eridania, but not S. frugiperda. Cry1Ac soybean provided poor control of all Spodoptera species. Nonetheless, Spodoptera larvae surviving on both Bt and non-Bt soybean were controlled by flubendiamide and thiodicarb. Thus, integrated control tactics would provide effective management of Spodoptera species in Bt soybean fields in South America.

Global perspectives on field-evolved resistance to transgenic Bt crops: a special collection

“…1 and 2, ISAAA 2019). Some recent major plantings include 94% of the cotton in India in 2019 (12 million hectares of Bt cotton, ISAAA 2019), >73% of the soybean in Brazil in 2021–2022 (>30 million hectares of Bt soybean, Godoy et al 2022), and 84% of the corn in the United States in 2022 (30 million hectares of Bt corn; USDA ERS 2022, USDA NASS 2023). Many widely cultivated Bt plants each produce more than one Bt toxin to broaden the spectrum of pests targeted, kill single pests with 2 or more unrelated toxins to delay evolution of resistance, or both (Carrière et al 2016).…”