Evaluation of yieldgard transgenic resistance for control of fall armywormand corn earworm (Lepidoptera : Noctuidae) on corn

Fall armyworm, Spodoptera frugiperda (J. E. Smith), and corn earworm, Helic overpa tea Boddie, perennially cause leaf and ear damage to corn in the sou theastern USA. Development of transgenic hybrids expressing insecticidal en dotoxin from Bacillus thuringiensis (Bt) offers a new approach to managing these insects in field corn. Transgenic Pt hybrids with either the Bt11 or MON810 event, collectively known as YieldGard Technology, were evaluated fo r control fall armyworm and corn earworm in southern Georgia during 1998, w hich coincided with a severe outbreak of fall armyworm. YieldGard Pt resist ance consistently reduced whorl infestation and damage to low levels and al so reduced ear infestations and larval numbers per ear. However, larval est ablishment did occur on many ears of resistant plants, but once established in ears, larvae of both species developed more slowly and caused much less kernel damage on resistant than susceptible plants. We found no relationsh ip between YieldGard Bt resistance and corn grain aflatoxin concentrations. Yield responses were variable with the prevention of yield loss being prop ortional to the severity of insect damage. These results indicate that Yiel dGard resistance is effective in preventing significant losses to field cor n by fall armyworm and corn earworm. Further, evaluation under a variety of growing conditions and insect infestation levels is needed to clearly asse ss the value of YieldGard technology to corn growers in the Southeast.