Frequency of alleles conferring resistance to Cry2Ab2 corn in field populations of Spodoptera frugiperda (Lepidoptera: Noctuidae) in the south region of the United States

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a target species of transgenic corn expressing pyramided Bacillus thuringiensis (Bt) proteins in both North and South America. In 2013, a total of 150 F₂ two-parent families of S. frugiperda were established using single-pair matings of feral individuals collected from six locations in Texas, Louisiana, Georgia, and Florida. The objective of this study was to determine the frequency of resistance alleles in these populations of S. frugiperda to Cry2Ab2, a commonly expressed Bt protein in most pyramided Bt corn products. For each F₂ family, 128 F₂ neonates were screened on leaf tissue of Cry2Ab2 corn plants in the laboratory. Results of the F₂ screen suggested that resistance allele frequency in field populations of S. frugiperda to Cry2Ab2 was not high in the region. Out of the 150 families, only one family from Texas and three families from Louisiana were identified as potentially positive families that might possess Cry2Ab2 resistance alleles. Thus, the estimated frequency for Cry2Ab2 resistance alleles in S. frugiperda in the south region of the U.S. was ≤ 0.005. Additional study is being conducted to confirm the resistance in the three potentially positive families.