Identifying resistance in corn to southwestern corn borer (Lepidoptera: Crambidae), fall armyworm (Lepidoptera: Noctuidae), and corn earworm (Lepidoptera: Noctuidae)

Southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae); fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae); and corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae), are major insect pests of corn, Zea mays L., in the southern United States. Corn hybrids produced from resistant germplasm were evaluated together with Bt and nonBt commercial hybrids in field tests and laboratory bioassays for resistance to leaf and ear damage by southwestern corn borer, fall armyworm, and corn earworm. The Bt hybrids, Mp496 x Mp716 and Mp704 x Mp716, exhibited resistance to leaf feeding damage by southwestern corn borer and fall armyworm. The Bt hybrids sustained significantly less southwestern corn borer ear damage than their nonBt versions. Those genotypes expressing resistance to leaf feeding also showed resistance, as indicated by reduced larval growth or survival in laboratory bioassays based on lyophilized leaf tissue, to southwestern corn borer, fall armyworm, and corn earworm. Only the Bt hybrids expressed resistance when larval growth was evaluated in bioassays based on lyophilized husk tissues. Using both field tests and laboratory bioassays to assess resistance to these insects will enhance efforts to identify useful germplasm and determine factors contributing to resistance.