Susceptibility of a Field‐Derived Population of Spodoptera frugiperda to Different Pyramided Bt Traits Expressed in Cotton

Spodoptera frugiperda (fall armyworm) is one of the most destructive lepidopteran pests affecting cotton, maize, and soybean crops across tropical and subtropical regions. The use of transgenic crops expressing Bacillus thuringiensis (Bt) proteins has become a key strategy for its management; however, resistance evolution poses a serious threat to the sustainability of these technologies. This study aimed to evaluate the susceptibility of a field‐derived population of S. frugiperda to different pyramided Bt traits expressed in cotton cultivars against third‐instar larvae. Larvae were fed leaf tissues from five cultivars, including four Bt cultivars expressing Cry1, Cry2, and Vip3A proteins in different combinations and one non‐Bt control. Survival curves, cumulative mortality, and median survival time (ST 50 ) were evaluated over a 7‐day period. Results revealed that the pyramided traits Cry1Ac + Cry2Ab2 + Vip3A (≈60% mortality), Cry1Ac + Cry2Ab2 (≈57%), and Cry1Ab + Cry2Ae + Vip3A (≈55%) caused significantly higher mortality than the non‐Bt control and the Cry1F + Cry1Ac + Vip3A combination, which exhibited reduced efficacy (≈25% mortality). The Cry1Ac + Cry2Ab2 + Vip3A pyramid produced the most rapid decline in larval survival, reaching 50% mortality earlier than the other Bt treatments. Differences in larvicidal activity among Bt pyramids indicate that the efficacy of cotton events against S. frugiperda depends on the specific combination of insecticidal proteins expressed. The reduced performance of the Cry1F‐containing pyramid may reflect differences in susceptibility within the tested population and highlights the importance of continued monitoring of field populations exposed to Bt technologies. These findings provide comparative information on the susceptibility of a field‐derived population of S. frugiperda to currently available Bt cotton traits and may support future studies on resistance monitoring and insect resistance‐management programs.