Purdue News
Purdue News
|
|
July 31, 1998
Don't assume Bt is broken because borers are bitingWEST LAFAYETTE, Ind. -- For farmers fighting the corn borer, one of the most welcome arrivals in their fields was Bt-enhanced corn.For these same farmers, no arrival could be less welcome in their fields than corn borers munching their way through their genetically enhanced crop. However, entomologists at Purdue University caution farmers not to jump to the wrong conclusions at the sight of a few caterpillars in their corn. Although there are concerns that the corn borers may eventually develop resistance to Bt-enhanced corn, Larry Bledsoe, a Cooperative Extension Service entomologist at Purdue, said that some crop damage is to be expected even in the genetically modified crops. "No bag of Bt seed is pure. No quality control can manipulate the amount of control in each plant," he said. "If a farmer was in a field and found a couple of plants being chewed up by corn borers, that would be normal." 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 even other insects that don't belong to the Lepidopterous group of stalk-boring pests. 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. 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. Typically seed lots of Bt-corn contain a small amount -- less than 4 percent -- of plants that produce little or none of the protein. "This means that a few plants aren't expressing the Bt gene. That's to be expected," Bledsoe said. Another explanation for finding corn borer caterpillars in resistant corn may be that the Bt-corn was planted close to nonresistant fields. "If you plant next to a field with no resistance, some of those corn borers are going to come into the resistant field and feed along the edges for a while before they are killed," Bledsoe said. A third reason for corn borers in resistant corn is that the amount of resistance in the plants isn't consistent through the growing season. "There's a slow loss of resistance in the plant," Bledsoe said. "It's very strong at the beginning of the season, but later in the season the amount of resistance drops." Unfortunately, there's a fourth possibility for why a farmer might find corn borer caterpillars in the corn, and it is that a new strain of corn borers have evolved in that area. There have been more than 500 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 borer developing widespread resistance to Bt crops, but scientists know that it is possible. Several research studies have been able to create Bt-resistant caterpillars in the laboratory. If a farmer has taken all of this into account and still suspects that corn borers have developed resistance in a particular field, Bledsoe recommended that he or she take the following steps:
Source: Larry Bledsoe, (765) 494-8324; Larry_Bledsoe@entm.purdue.edu
Writer: Steve Tally, (765) 494-9809; tally@aes.purdue.edu; Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu
|
