Purdue News

November 20, 1998 Refuges for pests needed near Bt cornfields WEST LAFAYETTE, Ind. -- A coalition of scientists from land-grant universities is standing behind its 1997 recommendation that corn farmers who use Bt-enhanced seed to control the European corn borer set aside 20 percent to 30 percent of their acreage as refuges. Planting Bt-enhanced crops on a higher percentage of acres runs the risk of losing a popular form of pest control, the scientists warn in an updated report, because the corn borers may develop resistance to the protein in the Bt-enhanced corn that kills them. On the refuges, the corn borer would have to be left alone, or treated only with chemical insecticides. That would ensure that a population of non-Bt-resistant corn borers would be available to breed with insects that had developed resistance. The updated report by the scientists notes that because the corn borer travels short distances, it is important for these refuges to be set up on each farm, and not on widely distributed sites. "We now have preliminary scientific information to substantiate these recommendations," said Eldon Ortman, professor of entomology and associate dean of the Office of Agricultural Research Programs at Purdue University. "There are two years of information and research backing up the recommendations of this report. However, this is still preliminary information that hasn't been broadly tested in the field. "It may be that over time we find that a 10 percent refuge is adequate, but we'll only know that after we see what is happening in the fields on a larger scale and over longer periods of time. Right now we're running a gigantic field experiment with this technology." This recommendation puts land-grant universities in the middle between corporations and environmental groups. Many of the chemical companies and seed producers who produce Bt-enhanced corn have called for a 5 percent refuge, while some environmental groups have called for refuges as large as 50 percent of the planted acres. "The seed and chemical industry is saying that a 5 percent refuge is large enough, but the best science we can come up with is that 5 percent is inadequate," Ortman said. The updated report was issued by the by the National Association of State Land-Grant Universities and Colleges' North Central Regional Technical Committee on "Bt Corn and European Corn Borer." Ortman is the administrative adviser of the committee that prepared the report. "The report was developed by scientists from 20 states, plus Canada and Mexico, collaborating with a land-grant university research team," Ortman said. Although almost no genetically enhanced crops were used as recently as 1996, in 1998 one-third of the nation's corn fields were planted in Bt-enhanced varieties. Bt-enhanced corn was developed to fight the European corn borer, which as the No. 1 pest of corn causes losses each year exceeding $1 billion in the United States. Bt corn uses a portion of the genes of the bacterium Bacillus thuringiensis, which produces a crystal-like protein that kills the insect when it mixes with enzymes in the insect's gut. The crystal protein has no effect on people, animals, or most insects other than the Lepidoptera group. Organic insecticides containing Bt have been used on crops for more than 30 years. Scientists have moved the gene for this crystal protein from the Bt bacterium into corn plants, which allows the leaves and stalks of the plants to produce the crystal protein. The problem is that in any population of corn borers, there are a few insects that aren't affected by the crystal protein. These resistant corn borers are so rare that they typically aren't any concern to farmers. Under normal circumstances, the resistant corn borers will most likely mate with others that aren't resistant, and will produce offspring that also aren't resistant. The problem comes from using too much of a good thing. If nearly all of the corn borers are killed by the Bt, only resistant insects will be available for mating. Soon, all of the borers produced in that area are resistant to the Bt-corn, and the enhanced corn loses its effectiveness. There have been more than 300 examples of insects that have developed resistance to various chemical insecticides, and widespread overuse of genetically enhanced crops could cause the same thing to happen with those control methods. There are no known incidents of corn borers developing widespread resistance to Bt crops, but scientists predict that it is likely to occur. Several research studies have been able to create Bt-resistant caterpillars in the laboratory. Ortman said that more information is needed about the biology of corn borer before the precise size of refuges is determined. "The big open or unanswered question is one of genetics, mating and movement," he said. "We need to know more about the genetics and biology of the organisms so that we know what the potential for the development of resistant varieties is. It all goes back to basic biology, we need to know more so that we'll know how to effectively manage this technology." Source: Eldon Ortman, (765) 494-8363; e-mail, eeo@aes.purdue.edu Writer: Steve Tally, (765) 494-9809; tally@aes.purdue.edu Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu To the Purdue News and Photos Page