Bt Sweet Corn Sours Hungry Caterpillars

By Jan Suszkiw
April 2, 1998

Crop-hungry caterpillars could be in for a fatal case of indigestion. That's the latest word from a team of scientists from Novartis Seeds, Inc., and USDA's Agricultural Research Service in Tifton, Georgia. They are evaluating new hybrid lines of sweet corn Novartis bioengineered to produce a toxin from the bacterium Bacillus thuringiensis.

The Bt hybrids carry a gene Novartis licensed from Monsanto Co. under the Yield Gard trademark. After they've been approved by the EPA, these hybrids could help reduce chemical insecticide applications. In Florida, which produces much of the nation's fresh market corn, farmers must often spray up to 40 times a season to ensure unblemished, worm-free ears. This spraying can endanger beneficial insects and the environment.

In the genetically enhanced sweet corn, the Bt toxin would be produced throughout the plant where caterpillars feed. Bt toxins don't harm humans, livestock, beneficial insects or other animals. But in corn earworm and fall armyworms, the toxin ruptures the caterpillar pests' gut tissues. The result: They either stop feeding or die.

That's what ARS entomologists Bill Wiseman and Robert Lynch observed during feeding trials. In one experiment, they placed 3-day-old hatchling worms on a diet of silks from four different Bt corn lines. They then monitored their growth and feeding behavior--and subsequent death. After about a week, 100 percent of the worms had died. Larger, six-day-old worms placed on the same diet didn't fare much better; only 10 percent survived after 10 days.

In field plots, Wiseman and colleagues saw less kernel feeding damage per square centimeter on Bt corn ears than on several resistant or susceptible check varieties. More studies are planned to see if "spot" insecticide use will mean even less kernel damage.

Scientific contacts: Robert Lynch, Bill Wiseman, Insect Biology and Population Management Research Laboratory, Tifton, Georgia, phone (912) 387-2375, fax (912) 387-2321, rlynch@tifton.cpes.peachnet.edu