News Releases: Iowa State University

QUICK LINKS
Today's News
News releases
ISU homepage

NEWS RELEASE

06-25-01

Contacts:
John Obrycki, Entomology, (515) 294-8622
Skip Derra, News Service, (515) 294-4917

NEW STUDY QUESTIONS WIDE SPREAD USE OF BT CORN TO COMBAT CORN BORER

AMES, Iowa -- Not since the introduction of synthetic insecticides in the 1950s, has agriculture seen such a potentially powerful technology as genetically altered plants to fight pests. But that potential must be weighed against the risks of using it, according to a paper published in the May 2001 journal, BioScience.

Genetically altered Bacillus thuringiensis, or Bt corn, is one such technology. While it does have a place in agriculture today, it should be used with restraint and thoughtfulness as scientists learn more about its risks as well as its rewards, according to John Obrycki, professor of entomology at Iowa State University and lead author of the paper. This is especially important in light of evidence that the use of Bt corn has not lessened the use of insecticides nor has it significantly increased yields.

The article, "Transgenic Insecticidal Corn: Beyond Insecticidal Toxicity to Ecological Complexity," is a review of recent scientific studies that detail Bt corn's effects on insects and other microorganisms. It also looks at planting rates of Bt corn, use rates of insecticides and yield studies of resultant crops from U.S. Midwest states that make up the "corn belt."

Co-authors with Obrycki are John Losey, assistant professor of entomology at Cornell University, Ithaca, N.Y.; Orley Taylor, professor of entomology and ecology and evolutionary biology at the University of Kansas, Lawrence; and Laura Jesse, a graduate student working under Obrycki's direction at Iowa State. BioScience is the journal of the American Institute of Biological Sciences.

Bt corn was developed in the 1990's and touted as a way for farmers to battle the European corn borer without having to apply insecticides. The altered corn produces insecticidal proteins derived from genes of the Bt bacterium, making the corn resistant to corn borers, bollworms and other pests. Most toxicity tests show that Bt corn has been very effective in combating the corn borer.

But Bt corn has been controversial too. Many European countries shy away from products made of Bt corn and studies over the past two years -- one by Losey in 1999 and one by Obrycki in 2000 -- have shown the pollen from Bt corn is harmful to Monarch butterfly larvae, significantly raising their mortality rates in controlled experiments.

Yet, Bt corn has been very popular with U.S. farmers, with areas planted rising from 2.8 million hectares of Bt corn in 1998, to 9.7 million hectares in 1999 and 6.2 million hectares in 2000. Up to 30 percent of the acreage in the Midwest has had some variety of Bt corn planted in it.

But Obrycki and his co-authors state that several studies show Bt corn use has not reduced insecticide use. In fact, Bt corn appears to be widely used as "insurance" against the possibility of corn being attacked by the corn borer rather than to fight an actual problem.

"Unlike the use of transgenic potatoes and cotton, the use of transgenic corn will not significantly reduce insecticide use in most of the corn growing areas of the Midwest," the scientists state. "Bt plantings are not being used as a replacement for insecticides, but in addition to them."

"We feel there is a limited role for Bt corn in relation to its use for controlling the European corn borer -- that is, use it if corn borer numbers have been consistently high," Obrycki added. "Planting it over 20 to 30 percent of the acreage in the Midwest seems to be overkill. It's not necessary relative to the value of the field corn and the importance of the corn borer as a pest."

In terms of corn yields, use of the Bt product has not significantly increased yields, the scientists state. Iowa State University Extension studies that compared transgenic and genetically similar non-transgenic corn hybrids grown in replicated plots in Iowa showed "only 34 percent of the transgenic lines produced significantly higher yields in 1997." Where corn borer damage was highest in non-transgenic lines, 50 to 58 percent of the transgenic hybrids produced significantly higher yields. When corn borer densities were generally lower than usual in Iowa, 12 percent of the transgenic lines produced significantly higher yields.

"The economic benefits of this technology are highly dependent on the population densities of the corn borer and the market value of the corn," the scientists state.

"This is a very powerful technology and may be useful for other insects, but does it really have a good role to play in the Midwestern U.S.?" Obrycki asked. "From our point of view, based on the past two or three years of data, the answer would be no."

What is needed, the scientists state, is a more encompassing approach to testing of this new technology. Current regulations that allow the use of Bt corn focus too narrowly on the toxicity aspects to a specific insect species.

Such regulatory testing and approval should include its effects on corn borer parasites (which also act as a control of the pest), non-target species (like Monarch butterfly larvae), pollinators (bees) and other microorganisms.

"We believe that a more comprehensive approach is required, one that considers the ecological complexity of agro-ecosystems," the scientists state. The "potential risks are not thoroughly addressed in the U.S. governmental registration process, an oversight that should be attended to."

- 30 -

Editors: For a copy of "Transgenic Insecticidal Corn: Beyond Insecticidal Toxicity to Ecological Complexity," call Skip Derra, ISU News Service (515) 294-4917 or email ssderra@iastate.edu. Obrycki is traveling the week of June 25. He can be reached during his travel at (815) 628-7006, and he checks his email (jobrycki@iastate.edu) on a regular basis.