Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 1999
Publication Date: N/A
Interpretive Summary: Fall armyworm larval feeding causes extensive damage to corn plants resulting in substantial yield losses. USDA-ARS scientists at Mississippi State University have developed and released corn germplasm with resistance to fall armyworm. Recently commercial seed companies have developed corn hybrids with genes from the baterium Bacillus thuringiensis (Bt). These hybrids also exhibit resistance to several lepidopterans. In this investigation four types of hybrids were evaluated for resistance to fall armyworm in field tests and laboratory bioassays. Hybrids that had both native genetic resistance and Bt genes sustained the least damage; hybrids with either native genetic resistance or genes from Bt, but not both types of resistance, showed a lower level of resistance; and standard commercially available hybrids showed the highest levels of damage. Larvae that fed on the standard commercial hybrids were more than ten times as large as those that fed on the Bt hybrids, and larval survival was more than ten times as great. Hybrids in which native genetic resistance and genes from Bt are combined offer promise for reducing losses from fall armyworm for corn producers.
Technical Abstract: Fall armyworm, Spodoptera frugiperda (J. E. Smith), is a serious pest of corn, Zea mays L., in the south. Larvae feed extensively on leaves and other parts of the plant. Germplasm exhibiting a moderate level of resistance to damage has been identified and released. This germplasm has been used in breeding programs for developing corn hybrids with resistance to fall armyworm and other Lepidoptera. In recent years, much effort has also been devoted to developing corn hybrids with genes from Bacillus thuringiensis (Bt) that encode insecticidal proteins. Some of these hybrids have exhibited moderate resistance to fall armyworm damage. In this investigation hybrids with both native genetic resistance and genes from Bt encoding insecticidal proteins were evaluated for resistance to fall armyworm in field tests and laboratory bioassays. Hybrids with both types of resistance sustained less fall armyworm damage than hybrids that had only native genetic resistance or genes from Bt encoding insecticidal proteins alone. Larvae that fed on hybrids with both types of resistance were significantly smaller after feeding on plants in the field or on lyophilized leaf tissue in a laboratory bioassay for 10 d than larvae fed on susceptible hybrids or hybrids with only one type of resistance. Both traditional host plant resistance and transformation of corn with genes from Bt provide hybrids with modreate levels of resistance, but when used together, they are complementary. Deployment of hybrids with both types of resistance should reduce losses to fall armyworm and also reduce the rate of buildups of resistance to Bt in fall armyworm populations.