In September 2000 a coalition of anti-GM groups discovered StarLink DNA in Kraft’s taco shells in Washington, D.C., grocery stores. Evidently, some growers were not strictly segregating StarLink corn from other varieties; the chaotic journey from field to supermarket aisle probably contributed to the muddle as well. In the first-ever recall of a GM food, Kraft, Taco Bell and other food companies yanked millions of dollars’ worth of taco shells off the shelves and out of restaurants. More than 30 people reported ostensible allergic reactions to StarLink, but after evaluating blood samples the FDA and U.S. Centers for Disease Control and Prevention found no evidence of true allergies. By November, however, the FDA had recalled another 300 corn-based products and the EPA began regularly screening the food supply for StarLink. Remnants of StarLink have been “virtually nonexistent since 2003,” the EPA says on its Web site; the organization is so confident in its disappearance that is has stopped screening.
How Bt crops threaten insect ecosystems and the environment is much less straightforward than whether they are safe enough to include in our diet. The massive mat of monoculture rolled across the U.S.—vast adjacent fields, each consisting of a single crop—is a relatively new kind of man-made ecosystem that has replaced much more diverse wild habitat. Long before GM plants of any kind, farmland displaced many native species. Still, cropfields are abuzz with life, some of which has evolved to survive on the farm. Overall, Bt crops around the world have been a boon for all kinds of insects and arthropods because this highly selective form of pest control has greatly diminished the use of chemical pesticides that kill buggy friend and foe alike. Bt crops reduced insecticide applications in the U.S. by 56 million kilograms between 1996 and 2011, according to one estimate. A recent experiment examined insect populations in 36 different sites in northern China using data collected between 1990 and 2010. Widespread adoption of Bt cotton buoyed the numbers of ladybugs, spiders and lacewings—all of which eat pests like aphids and do not harm crops.
Some Bt toxins may poison insects other than agricultural pests, but so far this danger seems to be negligible, especially when contrasted with the most likely alternative: the carnage of synthetic insecticides. In a small but widely publicized 1999 study, 44 percent of monarch butterfly larvae that ate milkweed leaves dusted with Bt corn pollen died. Monarch caterpillars feed exclusively on milkweed, and butterflies lay their eggs on milkweed plants growing near and within cornfields throughout the summer, when corn pollen abounds. Many scientists quickly pointed out serious flaws in the study, however, such as the fact that it did not quantify the amount of ingested pollen. Other teams of researchers performed more careful follow-up experiments and concluded that some forms of Bt pollen are harmful to monarchs in concentrations greater than 1,000 grains for every square centimeter of milkweed leaf; only 170 grains per square centimeter, on average, coat milkweed growing among cornfields. Pollen from one of the earliest strains of Bt corn, however—Bt 176—was toxic to butterflies at just 10 grains per square centimeter. A few years later Bt 176 had been largely phased out of the U.S. market.
Accumulating evidence indicates that in a few rare instances, researchers may have overlooked how Bt crops threaten other benign bugs. In a recently published three-year study, researchers found fewer ladybugs among plots of Bt corn than in fields of nonengineered corn—and insects living in the former died sooner on average. Bt corn, however, was still much less harmful to ladybugs than chemical pesticides. As for honeybees and native bee species, studies have consistently failed to find any evidence that Bt toxins hurt the pollinators.
Far more worrying to farmers—and ultimately to ecologists as well—is how quickly destructive insects become impervious to Bt crops. "Any entomologist would be stupid to say you’re not going to get resistance," says Brian Federici, an entomologist and Bt expert at the University of California, Riverside. Whenever farmers fight pests the same way over and over again, pests adapt and outwit that strategy. Consider one of the oldest methods of pest control: crop rotation. By growing different kinds of plants in the same field each season farmers can disrupt insects’ life cycles. Corn rootworm beetles lay their eggs on corn in the fall so that when their white larvae hatch in the spring they can feast on the plants’ roots. But if larvae find themselves surrounded by soybeans instead, they will have nothing to eat. Several species of corn rootworm eventually caught onto this trick. Some have evolved delayed hatching, emerging a year two later than usual, when a farmer is more likely to be growing corn again. Others have adapted by laying their eggs among soybeans instead of corn, since a soybean field will probably be a cornfield the following season.
Farmers will always be in an evolutionary arms race with pests regardless of whether they grow organic, use chemical pesticides or choose Bt crops. Where Bt crops have the advantage, however, is in delaying pest resistance for longer periods of time than any other pest-control strategy—if they are carefully engineered and grown responsibly. Bt crops are most effective when farmers and biotech engineers satisfy two key conditions. First, researchers must make the crop extremely lethal to the target pest, ideally killing 99.99 percent of any invaders. That way if some insects do evolve immunity, they will likely have two copies of the genetic mutation that made them immune; any pest with a single copy of the gene would not have been strong enough to survive. Second, farmers are supposed to grow Bt crops alongside “refuge areas”—blocks or strips of conventional crops where pests can prosper. As a consequence, the few pests that evolve resistance among the Bt crops will mate with the much more numerous susceptible insects in the refuges, diluting the genetic mutations responsible for their immunity and producing offspring that are vulnerable to Bt crops.
This is not a foolproof scheme, but when both biotech companies and farmers follow the rules, it works extremely well. In 1996, when Bt corn and cotton were first commercialized in the U.S., some researchers predicted that pests would evolve resistance within three to five years. In most cases this forecast was far too pessimistic. Farmers in the U.S. have been growing Bt corn designed to slay the European corn borer for 17 years without any evidence of resistance whatsoever. In contrast, when Bt crops do not kill a high enough proportion of insects or farmers do not devote enough land to refuges, Bt can become nearly as costly to farmers and the environment as chemical insecticides.
The EPA requires farmers to grow refuges alongside most, but not all, Bt crops. In general, entomologists recommend refuges comprising between 20 and 50 percent of a given field. In some cases, however, the EPA has lowered its refuge requirements to as little as 5 percent of total acreage. And "for some pests, such as cotton bollworm, refuge requirements have been abolished in large areas because Monsanto produced data suggesting natural refuges would be abundant enough," explains Yves Carrière of the University of Arizona. "Personally, I think it’s a risky decision." Data suggests that U.S. farmers have become less compliant with the EPA's regulations over the years; after all, a refuge area will probably endure more pest damage and produce a smaller harvest.
At least three kinds of pests around the world have developed some level of resistance to Bt: one in Puerto Rico, one in the continental U.S. and one in South Africa. Carrière and his colleague Bruce Tabashnik think two other pests in the southeastern U.S. and India may have become less vulnerable to Bt as well, although other researchers disagree. Considering that Bt crops target 13 major pests—and more than 50 different pests overall—that’s an excellent track record. Still, despite the general preparedness of farmers and scientists, a few pests evolved resistance to Bt toxin with unexpected swiftness.
The most recent and alarming example in the U.S. is corn rootworm, the story of which is documented in studies by Aaron Gassmann of Iowa State University and his colleagues. The first Bt crops designed to kill rootworm hit the market in 2003. Given the ongoing success with other Bt crops at the time, most researchers thought the pests would evolve resistance in 15 to 20 years. By 2009, however, some farmers in Iowa, Minnesota, Nebraska and other states spotted pockets of Bt corn that had fallen over—a classic sign of root damage. Whereas Bt corn tailored to destroy European corn borer kills 99.9 percent or more of pests, Bt corn engineered to eradicate rootworm is less reliably lethal, killing 85 to 98 percent of the larvae. Biotech companies and the EPA nonetheless figured that the benefits outweighed the risks.
It seems they miscalculated. Unbeknownst to researchers, rootworm populations already had relatively common variants of genes for resistance to cry toxins, explains the University of Minnesota’s Ostlie. Perhaps they evolved those genes in response to the ubiquitous presence of B. thuringiensis itself. Planting Bt corn only multiplied the frequency of resistance genes by creating an environment in which larvae carrying such genes had the best chance of surviving, mating and laying eggs. And any farmers failing to plant refuge areas made things worse. Some farmers whose Bt crops have succumbed to rootworm have now resorted to chemical insecticides. A similar but even worse situation unfolded in Puerto Rico, where man-made refuges were practically nonexistent and fall armyworm became impervious to Bt corn just three years after the crop's introduction in 2003. By 2007, seed companies had voluntarily pulled that variety of Bt corn from the Puerto Rican market.
In India and other developing countries rural farmers may not know about refuge requirements, if they exist at all; others will outright ignore them because they do not have the space or cannot afford to devote any land to vegetables that will probably become a buffet for bugs. Since introducing Bt cotton in 2002 India has become the second-largest producer of cotton in the world, after China. So far cotton pests are not worryingly resistant. One explanation is that India's farmlands are generally more diverse than those in the U.S., varying greatly within and between districts; the hodgepodge of different crops creates natural refuges. Many researchers argue that concerns about pest resistance should not stand between GM crops like Bt brinjals and the rural farmers that sorely need them. "The general idea is to get the plants out there, monitor changes in pest susceptibility and modify as we go along," says Anthony Shelton of Cornell University, who develops insect management strategies for vegetable crops and has worked extensively on Bt brinjals in India.
To address increasing pest resistance, Monsanto, Syngenta and other biotech companies have started selling seed mixes of 5 to 10 percent conventional corn or cotton and 90 to 95 percent Bt crop. When using such a "refuge in a bag," farmers do not have to go to the trouble of designating sections of their land as refuges; the conventional crops and Bt crops automatically intermingle wherever growers plant the seed mix. Such planting should be especially effective at delaying resistance in species like rootworm, the adult beetles of which tend to mate with nearby insects rather than traveling to a different part of a field. A mosaic of Bt plants and typical crops makes it difficult, however, for farmers to treat only damaged plants with pesticides. Biotech companies have another solution: they are expanding their inventory of "pyramid" Bt crops engineered with two or more toxins against the same bug. Even adding one more toxic protein to a Bt crop makes it far more difficult for pests to acquire immunity because they must not only evolve multiple genetic mutations but also inherit enough copies of each of those mutations to survive. Of course, if an insect has already evolved resistance to one of two toxins a plant makes, there's really only a single hurdle left.
In parallel to steering insect evolution, Bt crops may also alter other plants in unintended ways by mating with them. Because of differences in the shapes and sizes of pollen grains and the floral pads to which they stick, most plants can only pollinate their own species and closely related ones. Whether genetically engineered or not, many crops pollinated by insects or the wind inevtiably exchange genes packaged inside pollen grains with nearby fields of the same crop—including those owned by different farmers. Cotton and soybean flowers can pollinate themselves without much assistance; their pollen is generally not windborne, but it will hitch a ride with insects when they are around. Corn pollen, however, can travel half a mile in a few minutes in a moderate wind, despite being relatively large and heavy. Most likely, insects and gusts of wind have already scattered genes meant to stay within Bt cornfields—and other genetically engineered crops—among receptive neighbors. With an assist from people and modern transportation, such transactions seem to have surreptitiously crossed country borders as well.
In the fall of 2000, David Quist, then at the University of California, Berkeley, discovered genes from Bt crops in corn growing in the mountains of Oaxaca, Mexico—where GM crops were not approved. Farmers in Mexico may have planted imported GM corn kernels that were intended only for animal feed; once grown, they could have spread their genes to nearby cornfields. Other scientists questioned Quists’s results, however, and pointed out inadequacies in the way he tested for introduced genes. In 2003 Allison Snow of The Ohio State University and her colleagues collected kernels from 870 corn plants in 125 Oaxaca fields and searched them for genes from GM crops. They found none. But in two later experiments, Elena Alvarez-Buylla of the National Autonomous University of Mexico and her team scrutinized corn in Oaxaca and discovered the same genetic sequences Quist originally uncovered. “I think it’s inevitable that GM corn has gotten into Mexico and will continue to cross borders,” Snow says. She thinks the incidence is very rare, though, explaining the discrepancies between her studies and later surveys.
Whether such cross-pollination is beneficial or harmful depends entirely on the plants and genes in question and whether you look at the situation from a plant or person’s perspective. In one of Snow’s studies, the offspring of Bt sunflowers and their wild counterparts deterred caterpillars much more effectively than typical sunflowers and produced an average of 55 percent more seeds. That would be fantastic for wild sunflowers but horrifying for farmers in the Midwest who regard the pervasive seed-spewers as weeds that compete with their crops. In the U.S., corn, cotton and soybean have few if any closely related native species, so the chances of Bt genes finding their way into wild cousins are small. In contrast, were Bt brinjal commercialized in India, it could spread the Bt gene among the many different types of wild and cultivated eggplants. Such promiscuity would probably benefit most domesticated cultivars and would be unlikely to give wild weedy eggplant relatives a large enough survival advantage to make them a nuisance. Wild brinjal cousins are already far hardier than the eggplants farmers grow to eat. “Cultivated eggplants are pretty much wimps—they are watered, fertilized and protected,” Shelton says.
For the past four years, much more resilient eggplants have been poised to join corn, cotton and soybeans as the major Bt crops grown worldwide. All the available evidence—including research in India itself—confirms the safety of Bt crops for human consumption and demonstrates that their advantages vastly outweigh their risks. "If you take a global perspective, are things better since Bt crops? Absolutely, yes," says Tabashnik of the University of Arizona. "Now the question is: how can we optimize the use of these crops to maximize benefits?" Yet the moratorium Minister Ramesh originally imposed on Bt eggplants in 2009 stands stalwart with no signs of crumbling anytime soon, even though a new minister took his place. Gorgeous, healthy Bt brinjals exist, but they are trapped in the fenced-off fields of organizations that intended them for the public. "The past three years have been a very, very rough ride," Kumar says. "Environmental lobbies, anti-GM lobbies and anti-biotech lobbies are having a field day, going largely unopposed. Scientists do not speak much and, if they do, they do not speak in loud tones."
On August 23 India’s Supreme Court was scheduled to meet and review a report by the latest expert committee tasked with assessing the safety of Bt brinjals. In the days before the meeting, Kumar tried to stay optimistic, but he knew that, in all likelihood, nothing would change. Indeed, for vague reasons, the report was “not available to the government counsel.” So the eggplant fruit and shoot borer will continue to worm its way into the majority of cultivated brinjals; farmers will keep soaking their crops in pesticides; and, instead of transforming eggplant farming across India to the benefit of millions of people, insects and the environment alike, the plants that could change everything will remain under indefinite house arrest.