The European corn borer costs U.S. farmers more than $1 billion each year.
Many of the transgenic crops being planted in American corn and cotton fields are supposed to give plants do-it-yourself resistance to insects. This trick is done by inserting a gene that makes a protein that injures the gut of chewing insects. The protein, normally made by a soil bacterium called Bacillus thuringiensis, or Bt, does not affect mammals, fish, or the beneficial insects that eat crop pests.
The many advantages of Bt's crystalline proteins have made the material a mainstay of organic agriculture and the largest-selling biological insect control. The Bt genes in field corn are intended to defeat European corn borers. Just one larva from this moth can reduce a corn plant's production by 5 percent, says John Wedberg, a University of Wisconsin-Madison entomology professor who studies the little pests. In 1996, a heavy infestation of European corn borers cost American corn farmers $1 billion -- out of total corn receipts of almost $25 billion. Nevertheless, many farmers do not spray for European corn borers, as the damage is often subtle.
Different strokes for different folks
Various seed companies have introduced seeds with different Bt proteins that protect crops in different ways. Monsanto's YieldGard corn makes Bt proteins throughout the plant, while other corn varieties make Bt proteins in only certain plant parts.
Both photos courtesy John Wedberg, University of Wisconsin-Madison.
As with the genetically engineered Bt seeds sold for potatoes and cotton, the intended benefit is simple: Since the corn is poisonous to the borers, there is no need to kill them with chemical insecticides. The seeds are being sold as a classic win-win deal. The insects die, so the yield is higher. Farmers who were spraying save the expense of insecticides and the health hazards of chemical exposure. Because Bt is selective, it does not harm beneficial insects. And because Bt breaks down quickly, it does not pollute groundwater, a problem with many conventional pesticides.
It sounds great, at least when it works. But it doesn't always. About two dozen Texas cotton farmers have sued Monsanto and the Delta Pine Company, which sold seeds containing Monsanto's genetics. They claim that more than 18,000 acres of Bt cotton planted in 1996 were overwhelmed by insects.
Not working is the kind of obvious problem that the market can take care of. But some scientists warn about a more subtle hazard -- that insects may evolve ways to overcome the built-in insecticide. Entomologists have known for decades that the battle between insects and insecticides -- whether created by the plant or sprayed on it by a farmer -- is never finished. If you invent a new insecticide, eventually insects evolve to defeat it. And many scientists expect the same thing to happen with plants bred to make insecticide.
In fact, many experts think insect resistance is only a matter of time...
