Should India say yes to Bt crops?

By Debashis Banerji & Mihir Shah

IN JUNE this year, the Genetic Engineering Approval Committee (GEAC), set up by the Government of India for licensing genetically-modified (GM) crops, deferred the commercialisation of Bt cotton. The GEAC decided on large-scale trials to be conducted in different agro-climatic conditions, henceforth under the direct supervision of the ICAR. The spokesperson for the Confederation of Indian Industry termed it an ``unfortunate decision... a classic example of bureaucratic delay''. The Chairperson of the GEAC, Mr. A. M. Gokhle, defended it saying, ``as the technology is new to us, we did not want to take any chance''. Is the GEAC right in adopting a cautious approach? Why do we not try to learn from the experience of this technology, especially in the U.S. where it is not so new?

We must begin by mentioning that the spray of Bt or Bacillus thuringiensis, a common soil bacterium, is probably the single most important biological pest control technique in use worldwide.

What the genetic engineers have done is to develop transgenic crops containing the insecticidal gene of Bt, so that the plant itself makes the protein necessary for protection against pests. This has been perhaps the single biggest commercial application of r-DNA technology in the world so far. Cotton, corn and potato engineered with this gene were grown commercially in the U.S. for the first time in 1996. Companies producing these transgenic crops promote them as a way of reducing farmers' dependence on harmful pesticides. However, experience over the last five years reveals problems that place a question mark on this entire approach to pest control. In fact, there is growing concern that the very effectiveness of Bt as a bio-pesticide could be irrevocably endangered if use of Bt-transgenic plant varieties is not stopped immediately. Rigorous field studies of teams led by Bruce Tabashnik (University of Arizona) and Fred Gould (North Carolina State University), both reported in recent years in the Proceedings of the National Academy of Sciences, U.S., provide solid evidence of insect resistance to Bt cotton. Since resistance has become a major worry, companies now insist that farmers follow resistance management plans (RMPs), which include ``refugia'' (keeping a certain proportion of fields free of Bt seeds and insecticides). These fields are to be the refuge of susceptible insects, thus slowing down evolution of resistance against the Bt gene. However, Tabashnik's team has questioned two fundamental assumptions behind all Bt RMPs - that resistance to Bt is a rare recessive trait and that cross-resistance to Bt endo-toxins is uncommon. The idea that resistance could be delayed through the use of two or more endo-toxins has, thus, been seriously undermined.

Further, field data show that expression of toxins in Bt- transgenic crops can develop unevenly in different parts of the plant. In one report, Bt toxin expression was found to be 90-95 per cent in the top part of the plant but only 20-25 per cent in the lower nodes, making them more susceptible. Since the lower nodes often produce the highest quality cotton, their loss is even more significant. Bt toxin expression also typically starts out high in the early part of the season but tapers off over time. It is also inadequate in harsh environmental conditions such as drought. This ``sub-lethal dose'' of the toxin can facilitate the development of resistance over time, just as it happens with pathogenic bacteria when we fail to complete the necessary course of antibiotics. Uneven expression of Bt in the crop could also accelerate emergence of ``behavioural resistance'' (M. Harris, Science, 1996), because insects may sense which parts of the plant to avoid. In India, with so many difficult agro-ecological conditions and millions of poor farmers, Bt-transgenic crops are likely to grow unevenly across farms leading to many cases of sub-lethal doses of the Bt toxin and, therefore, resistance might be engendered at an even faster rate.

Estimates of how long resistance can be delayed vary, but the average figure in most research, even in the relatively favourable circumstances of the U.S., is not more than five years. So powerful demands are being made that the Environment Protection Agency (EPA) should delay any further approval of Bt- transgenic plant varieties, and that previous approvals should be reversed when evidence points to imminent failure of an RMP. In any case, the EPA had granted only conditional registration to Bt crops in 1995, mainly due to fears that pest resistance could develop. Unlike risks of conventional pesticides that are typically limited to specific circumstances of use and location, and can be conceivably tackled, risks following Bt-transgenic resistance are essentially irrevocable. Once resistance genes emerge and gain a foothold in populations, they cannot be recalled. And the worst part is that they would also foster resistance against the Bt spray, ultimately destroying the effectiveness of this safer bio-pesticide.

Even more worrisome than Bt cotton has been the history of StarLink, a transgenic Bt corn containing one of the family of Bt proteins (Cry9C), developed for control of European corn borer and Southwestern corn borer, and for suppression of black cut worm and corn stalk borer. Cry9C is a protein for which there is no history of human dietary exposure. It has several properties characteristic of food allergens. In August 1997, Plant Genetic Systems (later acquired by AgrEvo, subsequently taken over by Aventis) applied for registration of StarLink corn. The EPA approved its use in May 1998 only as animal feed and for industrial purposes. In April 1999, AgrEvo again petitioned the EPA to permit use of StarLink for human consumption. The EPA set up a Scientific Advisory Panel (SAP) comprising 16 physicians and independent scientists to advise it on the matter. In its report to the EPA in December 2000, the SAP concluded, ``there is a medium likelihood that Cry9C protein is a potential allergen'', thus rejecting the use of StarLink corn in human food. The SAP met once again in July 2001 to consider fresh studies by Aventis and others but found no reason to alter its recommendation of banning StarLink from human food. The panel found that Cry9C shows both heat stability and resistance to digestion, the two best available criteria presently known for ascertaining food allergy proteins. Too many questions remained about StarLink causing allergic reactions such as rashes, breathing problems, gastrointestinal upset or even anaphylactic shock.

Indeed, already in September 2000, some of America's favourite taco shells (Taco Bell), sold in grocery stores nationwide, were found to be illegally contaminated with StarLink. Kraft immediately recalled them from the market. Subsequently, nearly 300 other processed foods were also recalled following StarLink contamination. The registration of StarLink was cancelled and future planting of stocks of StarLink was prohibited. The U.S. Department of Agriculture and Aventis made aggressive efforts to remove StarLink from the market, all of which is expected to disappear by 2002.

The most extraordinary twist to this story is that even as the Americans were busy trying to get StarLink out of their system, the Clinton administration decided in October 2000, to lift export restrictions, allowing shipments of previously banned StarLink corn to Latin America, Asia and Europe. Of course, the vigilant Japanese Ministry of Agriculture immediately responded saying they would not allow StarLink corn to find its way into their food supply. It is to be hoped that the Indian Government will show the same sagacity and alertness to foil attempts to dump discredited and discarded products into our markets and prevent ``splicing'' of a doubtful technology into our thrust areas of research.

(The writers are, respectively, Director, Baba Amte Centre for People's Empowerment, and Secretary, Samaj Pragati Sahayog, both based in Madhya Pradesh.)

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