Susceptibility of Cry1F-susceptible and -resistant fall armyworm to transgenic corn plants containing single or pyramided Bt genes

Three greenhouse trials were conducted to evaluate larval survival and plant injury of Cry1F-susceptible, -resistant, and -heterozygous populations of the fall armyworm (FAW), Spodoptera frugiperda, on non-Bt and Bt corn hybrids containing single or pyramided Bt genes. A total of 13 corn hybrids were evaluated in three greenhouse trials. These corn hybrids included five non-Bt, two single-gene Bt (Herculex^® I and YieldGard^® corn borer), and six pyramided Bt (Genuity^® VT Double Pro^TM, VT Triple Pro^TM, SmartStax^TM, and Agrisure^® Viptera^TM) corn hybrids. Leaf damage rating (Davis’ 1 to 9 scales) of the resistant population on Cry1F corn plants was 5.5-6.0 after 7 d and 6.8-8.4 after 12-15 d in the three trials, which was not significantly different compared to those observed on non-Bt corn plants. After 12-15 d, live larvae were recovered from 44-100% Cry1F corn plants infested with resistant neonates. In contrast, no live larvae with little or no leaf injury were observed on the Cry1F corn plants that were infested with susceptible or heterozygous populations, suggesting that the Cry1F-resistant population was highly resistant to the Cry1F corn and the resistance was recessive. There was no survival with little or no leaf injury by any of the FAW populations on pyramided Bt corn plants, suggesting the pyramided Bt corn products can overcome the Cry1F resistance and thus should provide a means for Cry1F resistance management in FAW.