POSTED 4 MAY 2006
Planting season: Is insect-resistance a good thing?
As Northern Hemisphere farmers stick their seeds in the soil, we're wondering about genetically modified (GM) seeds. In 2005, biotech plantings grew 11 percent over 2004, to an estimated 222 million acres. That's more than twice the total area of California. And the seeds were only first made available to farmers in 1996.
Portugal, France and the Czech Republic all started growing biotech crops, raising the count of nations that permit biotech plantings to 21, and surging growth of genetically modified cotton in Brazil and China has fed the increase.
Proponents claimed that GM crops would boost production, allow cropping on salty or drought-stricken land, reduce use of pesticides, and allow a shift to less-toxic herbicides. After years of bragging about the ability to move genes among organisms, they retreated under criticism to a slightly different position. Moving genes, they argued, isn't really that new: farmers and plant breeders have been doing it ever since the birth of agriculture about 10,000 years ago.
But we also heard from doomsayers. It's one thing, critics argued, to swap genes among closely related species, which is how plant breeding gets done, but something else to move them, from, say, bacteria to plants. Critics worried that transferred genes would pollute wild crop relatives, ruining them as a source of new traits for plant breeders. They fretted that pesticides in the crops would kill beneficial insects, and that ownership of genes and seeds would give giant corporations an ever bigger slice of the agricultural pie and help drive smaller farmers out of business. They also warned that making crops resist common herbicides raised the danger that wild plants and weeds would gain that same resistance -- with unpredictable results.
After 10 years, and the planting of GM crops on a billion acres, what do you say we look over our shoulders and ask: Were the dangers real or hyped? Where is the scientific evidence of harm, what we'll call the dead bodies? And if there are no bodies, is that evidence of safety, or of poor oversight?
We'll save a related issue, the safety of GM food for those of us who eat it, for later. Here, the Why Files is seeking signs of environmental hazards caused by genetic engineering in agriculture.
Pray for (less) spray
Perhaps the biggest category of biotech crops is those that include bacterial genes so the crop can defend itself against insects. The primary source of genes is Bacillus thuringiensis (Bt), a bacterium commonly used as an insecticide by organic farmers. Bt makes crystals that are deadly to Lepidoptera, moths that are major plant pests. The biggest Bt crops are corn and cotton.
Big-time biotech seedmaker Monsanto crows that herbicide-resistant corn will be planted on a record 40 percent of American corn acreage in 2006. And millions of small farmers in China have adopted Bt cotton, a crop that is typically doused in insecticide. By itself, that usage refutes one common criticism: that GM crops would benefit large farmers at the expense of smaller ones. Indeed, notes Martina Newell McGloughlin, director of the Biotechnology Research and Education Program at the University of California at Davis," If you look at the actual numbers, 90 percent of farmers [adopting GM seeds] are resource-poor farmers." Of the estimated 8.5 million farmers now using biotech crops in 21 countries, she says, almost all are small-holders in developing countries. But in terms of acreage, the bulk of GM crops go to developed countries.
Studies in China by Carl Pray, of the department of agricultural, food and resource economics at Rutgers University, found that Bt crops required less pesticide. His surveys, conducted with Chinese colleagues, found roughly a 50 percent reduction in per-hectare pesticide use (see "Five Years of Bt Cotton..." in the bibliography).
Economics comes first
Pesticide exposure can harm a farmer's health, and Bt crops can reduce this exposure, but Pray says health does not seem a major motivation for the Chinese farmers. "They are concerned about pesticides, and aware that they are getting sick when they use too much pesticide, but farmers seem to be willing to spray every other day, even if it will give them headaches."
Rather, Bt cotton is planted because it is more profitable, Pray says. Bt yields are an estimated 5 to 8 percent higher than normal, and farmers "are seeing an increase in income through a reduction in pesticide use and labor." In 1995, farmers paid an average of $101 per hectare for pesticide, so lower cost for bug juice "more than offset the higher seed prices" (see "Five Years ..." in the bibliography).
Pray added that Bt has increased cotton production in China. That cut the crop's price, harming non-users of Bt seeds. The other losers, he says "are the chemical companies that used to sell a lot more pesticides."
However, cotton research published this week in Arizona shows that Bt seeds only increased yields when the GM crop can actually control insects. In many fields, conventional insecticides turned out to give better insect control and higher yields -- although that, in turn, killed more of the non-target insects (see "Farm-scale Evaluation..." in the bibliography).
The pesticide reductions seen in China appear to be widespread. A recent report found that globally, biotech crops use 14 percent less pesticide than comparable crops. In that study, pesticide use was measured by a technique called "environmental footprint" that factors both the quantity of toxicity of the various pesticides used.
One benefit of Bt crops is a reduction in the use of broad-spectrum pesticides, which kill non-target insects, including beneficial insects that eat pests. Pray cited anecdotal evidence that in the Chinese cotton, "you do get more species of bugs in the field in general, and do get more beneficial insects. There is a shift in the pest spectrum." Concerning biotech crops generally, Bruce Tabashnik, professor and head of the department of entomology at the University of Arizona, wrote us to say, "Extensive studies show little or no negative impact of Bt crops on non-target insects. In some cases, Bt crops reduce insecticide sprays, which benefits some non-target insects."
One key concern about Bt crops was the fear that insects would quickly evolve resistance to the bacterial toxins, rendering them useless. This has been particularly worrisome to organic farmers, who often rely on Bt insecticides.
When chemical insecticides were introduced, some farmers and farm experts dared to dream of a bug-free agriculture, but insecticides fail over time, says Richard Roush, of the statewide integrated pest management program in California. Just as bacteria evolve ways to defeat antibiotics, insects evolve ways to defeat bug-killing chemicals. After all, when vast acreages are treated with insecticide, billions of insects are exposed. Any individuals with a mutation that somehow outfoxes the bug spray will multiply and dominate the field.
That's called "insecticide failure," and it happens especially quickly in cotton. "New insecticides for cotton insects will fail within 7 years of use," Roush says, but this does not seem to be happening with bollworms.
The pink cotton bollworm is the major insect in Arizona's cotton fields, and it has not become resistant to Bt cotton, says Tabashnik. To slow the evolution of resistance, farmers are required to sow "refuges" containing non-engineered cotton. When a bug does evolve resistance to Bt, it is likely to mate with a normal bug from the refuge, diluting the genes for Bt resistance.
In China, Pray admits that he's noticed that after an initial drop-off in use of conventional insecticide when farmers started planting Bt cotton, they have begun increasing their sprays. While that could be evidence of bollworm resistance, he thinks it's more likely due to a change in the overall balance of bugs. Other pests have come in to fill the ecological niche left by the vanished bollworms.
Overall, says Tabashnik, the global picture is positive -- so far. "We are now a decade into Bt crops -- and a cumulative global total of over 100 million hectares -- with no documented cases of field-evolved resistance in pests. Scientists have been looking hard for pest resistance and other problems associated with transgenic crops. Although it is wise to continue close monitoring of GM crops on a case-by-case basis, the track record so far is excellent."
But you don't have to read beyond the title of his article to see that he eventually expects resistance to Bt (see "Delayed Resistance..." in the bibliography).
Have GM genes polluted corn in Mexico?
Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive