Field efficacy of sweet corn hybrids expressing a Bacillus thuringiensis toxin for management of Ostrinia nubilalis (Lepidoptera : Crambidae) and Helicoverpa zea (Lepidoptera : Noctuidae)

Field studies were done in 1995-1996 to assess the efficacy of three sweet corn hybrids that express the Bacillus thuringiensis (Bt) toxin, CrylAb, ag ainst two lepidopteran pests. Ostrinia nubilalis (Hubner) and Helicoverpaze a (Boddie). The Bt hybrids tested were developed by Novartis Seeds, using t ale event BT-11, which expresses Bt toxin in green tissue as well as reprod uctive tissues including the tassel, silk, and kernel. Bt hybrids were comp ared with a standard non-Bt control or tale non-Bt isoline for each hybrid; none of the hybrids were treated with insecticides during the study. Hybri d efficacy was based on larval control of each pest, as well as plant or ea r damage associated with each pest. In both ears, control of O. nubilalis l arvae in primary ears of all Bt hybrids was 99-100% compared with the appro priate non-Bt check. Plant damage was also significantly. reduced in all Bt hybrids. In 1996, control of H. zea in Bt hybrids ranged from 85 to 88% wh en compared with the appropriate non-Bt control. In 1996, a University of M innesota experimental compared with the appropriate non-Bt control. In 1996 , a University non-Bt hybrid (MN2 X MN3) performed as well as the Bt hybrid s for control of O. nubilalis. Also. in 1996, two additional University of Minnesota experimental non-Bt hybrids (A684su X MN94 and MN2 X MN3) perform ed as well as Bt hybrids for percent marketable ears (ears with no damage o r larvae). In addition, compared with the non-Bt hybrids, percent marketabl e ears were significantly higher for all Bt hybrids and in most cases range d from 98 to 100%. By comparison, percent marketable ears for the non-Bt hy brids averaged 45.5 and 37.4% in 1995 and 1996, respectively. Results from the 2-yr study strongly suggest that Bt sweet corn hybrids will provide hig h levels of larval control for growers in both fresh and processing markets . Specifically, Bt sweet corn hybrids, in the absence of conventional insec ticide use, provided excellent control of O. nubilalis, and very good contr ol of H. zea. However, depending on location of specific production regions , anti the associated insect pests of sweet corn in each area, some insecti cide applications may still be necessary.