Larval Survival and Plant Injury of Cry1A.105-Selected Fall Armyworm on Transgenic Corn Containing Single or Pyramided Bt Genes

Two whole-plant greenhouse trials and one leaf-tissue laboratory bioassay were conducted to evaluate larval survival and plant injury of one Bt-susceptible, two Cry1A.105-selected, and two heterozygous populations of the fall armyworm (FAW), Spodoptera frugiperda, on non-Bt and Bt corn plants containing single or pyramided Bt genes.11 corn hybrids/lines were evaluated in the study, which included four non-Bt, four single-gene Bt (Cry1F, Cry1Ab, Cry1A.105 and Cry2Ab2), and three pyramided Bt corn products. In the whole-plant greenhouse trials, live larvae were recovered from 51.4-58.3% Cry1A.105 corn plants infested with two Cry1A.105-selected populations, which were similar to those (35.4-81.9%) recorded from the non-Bt corn plants. In contrast, significantly lower survivorship (0-29.2%) were observed on the Cry1A.105 corn plants that were infested with the susceptible or heterozygous populations, suggesting that Cry1A.105-selected populations were resistant to the Cry1A.105 corn line and the resistance was semi-dominant. The Cry1A.105-selected populations also survived well on the Cry1F and Cry1Ab corn hybrids, while they exhibited low survivorship (0-6.3%) on the Cry2Ab2 and pyramided Bt corn. Data observed in the leaf-tissue bioassay were consistent with the greenhouse trials. The results demonstrated that these pyramided Bt corn products were effective for controlling the Cry1A.105-selected FAW populations.