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ARS Home » Southeast Area » Tifton, Georgia » Crop Protection and Management Research » Research » Publications at this Location » Publication #93108
Title: EVALUATION OF BT TRANSGENIC SWEET CORN HYBRIDS FOR RESISTANCE TO CORN EARWORM AND FALL ARMYWORM (LEPIDOPTERA: NOCTUIDAE) USING A MERIDIC DIET BIOASSAY

Author
item WISEMAN, BILLY - RETIRED USDA
item Lynch, Robert
item PLAISTED, D. - NOVARTIS SEED CO.
item WARNICK, D. - NOVARTIS

Submitted to: Journal of Entomological Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Currently, 20-40 applications of pesticide are used to produce sweet corn free of insect injury for the fresh or processing sweet corn markets. Sweet corn has been genetically engineered to contain a gene from a bacteria, Bacillus thuringiensis (Bt), that is toxic to some insects that feed on the ears. We developed a laboratory bioassay procedure whereby corn leaves, silks, or kernels of the Bt sweet corn were incorporated into an insect diet to measure their resistance to feeding by corn earworm and fall armyworm, two of the major insects that feed on the ears of sweet corn. Results from these bioassays were highly correlated to those where insects were fed fresh corn leaves, silks, or kernels. Thus, when time does not permit the conduct of bioassays during the busy summer months, the corn tissue can be freeze- dried, ground into a powder, and stored in a freezer and the bioassays can be conducted later.

Technical Abstract: A laboratory bioassay was used to evaluate Bt transgenic sweet corn hybrids for resistance against the corn earworm, Helicoverpa zea, and the fall armyworm, Spodoptera frugiperda. Whorl leaves, silks, and kernels, either fresh or oven-dried and ground with a mill, were incorporated into a dilute pinto bean diet and bioassayed against neonate, 3-, or 6-day-old larvae. Regardless of age of the larvae, results with the diet bioassay using fresh silks, oven-dried silks or fresh kernels were highly correlated with those for the fresh silk bioassay. Differences in susceptibility between insect species to the CryIA(b) toxin produced in the transgenic plants were also readily discernable using the diet bioassay. Based on results of the bioassays, Novartis sweet corn hybrids containing a cryIA(c) gene for delta-endotoxin production were very highly resistant to leaf, silk and kernel feeding by the corn earworm and highly resistant to leaf and silk feeding by the fall armyworm.