Sensitivities of Fall Armyworm (Spodoptera frugiperda) Populations in Different Regions of China to Four Bt Proteins

Fall armyworm (FAW), Spodoptera frugiperda, invaded the south of China in December 2018 and has since posed a huge threat to crop production in China. However, transgenic Bacillus thuringiensis (Bt) corn can efficiently control the damage caused by FAWs. In fact, the Chinese government has issued biosafety certificates for several Bt corn hybrids expressing any one of four Bt proteins, Vip3A, Cry1F, Cry1Ab, and Cry2Ab, or combinations thereof, to control FAWs. These Bt corn events are soon to be commercialized in China. Therefore, it is necessary to monitor and evaluate whether the FAW has developed resistance to any of the Bt corn hybrids planted in fields in China. To address this issue, we collected 11 geographical populations of FAWs and determined the sensitivity of each to the aforementioned four purified Bt proteins as assessed by diet surface overlay bioassays. The ranges for the 50% lethal concentration (LC50) of the four Bt proteins to all FAW populations were as follows: 11.42-88.33 ng/cm(2) (for Vip3A), 111.21-517.33 (Cry1F), 135.76-1108.47 (Cry1Ab), and 994.42-5492.50 (Cry2Ab). The corresponding ranges for the 50% growth inhibition concentrations (GIC(50)) were 1.43-14.86, 2.35-138.97, 1.58-464.86, and 25.01-1266.07 ng/cm(2). The lethal effects and growth inhibition effects of the four Bt proteins on FAW were in the same order of Vip3A > Cry1F > Cry1Ab > Cry2Ab. A comparison with published LC50 values of Bt proteins towards sensitive FAW populations revealed that all 11 FAW populations in this study were sensitive to Vip3A, Cry1F, and Cry1Ab. This study provides foundational data for monitoring and controlling the resistance of Bt corn to FAW in China.