Lethal and sublethal effects of DBN9936 and Ruifeng 125 Bt corn events on <i>Spodoptera frugiperda</i> (Lepidoptera: Noctuidae) under laboratory conditions

The DBN9936 event (expressing Cry1Ab) and the Ruifeng 125 event (expressing Cry1Ab/Cry2Aj) are the first genetically modified maize varieties granted biosafety certificates in China, primarily targeting Ostrinia furnacalis (Guenée). However, their lethal and sublethal effects on Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), an invasive pest first detected in China in 2018, remain insufficiently understood. This study evaluated the life table parameters of first- to third- instar S. frugiperda larvae fed on V6-V8 stage leaves of DBN9936 and Ruifeng 125 maize under controlled laboratory conditions. Corrected mortality after 7 d was 90.46%, 56.13%, and 6.52% for first to third instars on DBN9936 and 51.85%, 15.79%, and 12.45% on Ruifeng 125, respectively. Both Bt events significantly reduced pupation rate, pupal weight, and fecundity compared to non-transgenic controls. Additionally, larval development was prolonged by 10 to 16 d. Life table analyses revealed reductions in net reproductive rate (R0), intrinsic rate of increase (r), finite rate of increase (λ), and population growth trend index (I) for larvae fed on either Bt maize. Simulated migration scenarios further indicated that brief access to non-Bt maize before transitioning to Bt maize could allow larvae survival, potentially undermining Bt efficacy. These findings demonstrate that both DBN9936 and Ruifeng 125 exert significant lethal and sublethal effects on S. frugiperda, yet intermittent feeding and larval mobility between Bt and non-Bt plants may accelerate resistance evolution.