Evaluation of Bt transgenic sweet corn hybrids for resistance to corn earworm and fall armyworm (Lepidoptera: Noctuidae) using a meridic diet bioassay

A laboratory bioassay was used to evaluate Bt transgenic sweet corn hybrids for resistance against the corn earworm, Helicoverpa tea (Boddie), and the fall armyworm, Spodoptera frugiperda (J. E. Smith). 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 CrylA(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 crylA(b) gene 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.