Novel Vip3A Bacillus thuringiensis (Bt) maize approaches high-dose efficacy against Helicoverpa zea (Lepidoptera: Noctuidae) under field conditions: Implications for resistance management.

Sweet corn, Zea mays L., transformed to express a novel vegetative insecticidal protein, Vip3A (event MIR162, Syngenta Seeds, Inc..), produced by the bacterium, Bacillus thuringiensis (Bt), was evaluated over four field seasons in Maryland and two field seasons in Minnesota for efficacy against the corn earworm, Helicoverpa zea (Boddie). Hybrids expressing the Vip3A protein and pyramided in hybrids also expressing the Cry1Ab Bt protein (event Bt11, ATTRIBUTE(®), Syngenta Seeds, Inc.) were compared to hybrids expressing only Cry1Ab or to genetically similar non-Bt hybrids each year. In addition to H. zea efficacy, results for Ostrinia nubilalis (Hübner) and Spodoptera frugiperda (J.E. Smith) are presented. Over all years and locations, the non-Bt hybrids, without insecticide protection, averaged between 43 and 100% ears infested with a range of 0.24 to 1.74 H. zea larvae per ear. By comparison, in the pyramided Vip3A x Cry1Ab hybrids, no larvae were found and only minimal kernel damage (likely due to other insect pests) was recorded. Hybrids expressing only Cry1Ab incurred a moderate level of H. zea feeding damage, with surviving larvae mostly limited to the first or second instar as a result of previously documented growth inhibition from Cry1Ab. These results suggest that the Vip3A protein, pyramided with Cry1Ab, appears to provide the first "high-dose" under field conditions and will be valuable for ongoing resistance management.