Corn hybrid produces its own natural pesticide

Emily Dalnodar

Unusual combinations sometimes go surprisingly well together: peanut butter and jelly; men and women; even corn and Bacillus thuringiensis.
Bacillus thuringiensis, commonly called Bt, is a naturally occurring soil-borne bacterium with a protein that makes its own insecticide.
Scientists discovered Bt’s insecticidal properties in 1915, and by 1927 developed a Bt spray that effectively killed a crop’s worst enemy. In corn’s case, that enemy is the European corn border, a moth-like insect whose larvae bore into the stalks and ears, ruining the appearance and marketability of the corn.
According to a collaborative report by the University and several seed companies, corn borders are the most damaging insect pest of corn throughout the United States and Canada. A 1995 outbreak of the corn border in Minnesota alone created $285 million in losses, the report found.
Although the spray heavily curbed corn border damage, scientists raised the bar recently by actually “blasting” Bt DNA into corn DNA and creating a new product: Bt corn. The hybrid corn manufactures its own insecticide and, researchers say, eliminates the need to spray crops.
“We use a blast technique where the DNA is attached to gold particles and then, using a high-pressure system, it is blasted into the corn cells,” said Rob Venette, a graduate student studying Bt corn at the University. “A lot of the corn cells will die, but some will live. We have to go through and find the ones that survived. From there, we can make the Bt corn.”

You get what you pay for
Although Jim Rowe works alongside University researchers, he is actually a farmer, since he grows produce for profit. Rowe, a plant science manager at the University’s Rosemount experiment station, first encountered Bt corn when Venette and a group of students used field space next to his for experiments. He said their success with the crop prompted him to plant his own. Now part of the University’s annual income from crop sales includes Rowe’s Bt corn.
Several large seed companies, including Northrup King and Mycogen, have developed and manufactured the hybrid corn since 1996, when the Environmental Protection Agency approved its use. Since then, the corn’s cost-effectiveness has garnered growers’ attention.
“Bt corn seeds cost extra, but it works out in the end,” said Rowe.
A bag of 80,000 corn kernels costs roughly $100 and covers 2.5 acres. The same sized bag of Bt corn kernels costs about $130. But non-Bt corn requires insecticide spray twice per season at about $15 per acre — a cost the Bt farmer doesn’t need to pay.
So far, the price difference isn’t astronomical — roughly $45 per bag — but the advantage of Bt corn is its better yields. Insecticide spray only controls about 80 percent of first-generation corn borders and 67 percent of second-generation borders. Bt corn provides about 96 percent average control of European corn borders, resulting in a higher crop yield at season’s end.
Genetic strategizing
Despite the favorable findings, corn growers haven’t abandoned non-Bt corn for its genetically altered counterpart. Researchers said they hope that never happens.
“We’re trying to get off of the pesticide treadmill of a new pesticide being developed every five years because insects develop resistance,” Venette said. “We’re encouraging growers to grow insects that are susceptible to Bt corn by planting non-Bt corn.”
Researchers ask that farmers plant about 20 percent of their crop with non-Bt corn, called a refuge crop. So while mutant insects that resist Bt insecticide still survive, they will breed with a large gene pool of susceptible insects. The result is a second generation of corn borders not nearly as resistant.
The concept is sound, but some are loathe to waste 20 percent of their crop to voracious corn borders, Venette said. Farmers think year-to-year, not long-term, Venette said, so it’s hard to see past the good of temporary sacrifice when you need that extra cash.
But farmers have little choice with Bt. Several seed companies require each of their Bt corn purchasers to plant a refuge crop along with their normal crop to safeguard the hybrid corn’s market stability.
“To produce and develop a new insecticide is extremely difficult,” said Mike O’Brien, an AgrEvo seed company communications manager. “Seed companies want to see their product on the market for as long a time as possible.”
Since Bt is one of only two naturally occurring insecticides — photorhabdus is the second, and less researched — its role as an organic crop protector for farmers abiding by strict organic guidelines makes it a coveted resource. Once insects develop a resistance to Bt, organic farmers have little way to naturally defend their crops. If Bt’s potency wears off, farmers will have no natural way to protect crops, so researchers and seed companies alike prompt growers to take extra steps to ensure Bt’s survival.
AgrEvo already has 3,000 buyers signed up on the plan since launching their own patented Bt corn product a few years ago, O’Brien said.
A few more years must pass before researchers can evaluate the long-term effectiveness of refuge crops against corn border resistance, and Venette said Minnesota farmers will play a big role in that determination.
“Corn borders live in Minnesota year-round, so what Minnesota farmers do has a big influence on border evolution,” Venette said.