Submitted to: Journal of Agricultural and Urban Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2007
Publication Date: 4/1/2007
Citation: Williams, W.P., Buckley, P.M., Daves, C.A. 2007. Identifying resistance in corn to southwestern corn borer (Lepidoptera: Crambidae), fall armyworm (Lepidoptera: Noctuidae), and corn earworm (Lepidoptera: Noctuidae). Journal of Agricultural and Urban Entomology. 23:87-95. Interpretive Summary: Southwestern corn borer, fall armyworm, and corn earworm are major insect pests of corn in the southern United States. Corn germplasm lines with genetic resistance to leaf feeding by southwestern corm borer and fall armyworm have been developed and released by USDA-ARS scientists at Mississippi State University. Considerable effort has also been devoted to identifying germplasm with resistance to ear damage by these insects, but good sources of resistance have not yet been identified. The availability of transgenic corn hybrids transformed with genes from the bacterium Bacillus thuringiensis (Bt) provided a new approach to reducing losses from these insects. In this investigation, resistant hybrids from the Mississippi State breeding program were evaluated together with transgenic Bt commercial corn hybrids and non-transgenic hybrids for resistance to leaf feeding and ear damage caused by southwestern corn borer, fall armyworm, and corn earworm. Laboratory bioassays that used freeze dried leaf or husk tissue determined larval survival and growth for the three insect species. The assays using freeze dried leaf tissue should be useful in studying resistance to all three insects. The assays using husk tissue appear to be most promising for southwestern corn borer. Such assays should be useful in determining biochemical components of resistance.
Technical Abstract: Southwestern corn borer, Diatraea grandiosella Dyar; fall armyworm, Spodoptera frugiperda (J.E. Smith); and corn earworm, Helicoverpa zea Boddie, are major insect pests of corn, Zea mays L., in the southern United States. Corn germplasm with resistance to leaf feeding by southwestern corn borer and fall armyworm has been developed and released by USDA-ARS at Mississippi State, MS. Corn hybrids produced from this germplasm were evaluated together with Bt and non-Bt commercial hybrids in field tests and laboratory bioassays for resistance to leaf damage and ear damage by southwestern corn borer, fall armyworm, and corn earworm. The Bt hybrids, Mp496 × Mp716, and Mp704 × Mp716 exhibited resistance to leaf feeding damage by southwestern corn borer and fall armyworm. The Bt hybrids, Mp305 × Mp496, and Mp496 × Mp716 also exhibited resistance to southwestern corn borer ear damage. 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.