| The corn earworm (CEW), Helicoverpa zea (Boddie), is an annual pest of corn, Zea mays L. Larvae damage corn by feeding on vegetative and reproductive tissues. Monetary losses from CEW may be caused by reduced yields, invasion by secondary pests or pathogens, and reduced grain quality. Yet CEW management in field corn is not usually economically or environmentally advisable because multiple insecticide applications are required to obtain satisfactory pest suppression. The introduction of genetically engineered corn expressing a gene derived from the soil bacteria Bacillus thuringiensis Berliner (Bt) offers a potential tool for CEW management in field corn.; Field and greenhouse evaluations of three transgenic corn events (MON810, Bt11, and Bt176) suggest that vegetative-stage Bt corn is highly resistant to CEW. Assessments of CEW densities on corn ears revealed no difference in larval populations among Bt and non-transgenic corn entries. However, larvae infesting ears of YieldGard® entries (MON810 and Bt11) exhibited extended development compared with other transgenic (Bt176) and non-transformed plants. Evaluations of corn ear damage revealed up to 66% fewer total damaged kernels on YieldGard® protected plants than on non-Bt and Bt176 cultivars.; CEW feeding assays showed that larvae fed more frequently and grew more rapidly on untreated diet than when presented various Dipel® treated food sources. Larvae presented a choice of diets fed more frequently and grew more rapidly than those confined to Dipel®-treated food.; These results suggest that reproductive structures on Bt plants may not offer high levels of resistance to CEW when compared with larval suppression during vegetative growth. YieldGard® protected corn ears, however, did hinder larval development. Delaying development may reduce larval fitness and feeding frequency because of direct toxic effects and indirectly because maturing kernels constitute a less desirable food source. This protection should benefit producers by reducing yield losses and limiting secondary ear pests. |
