by GRAIN | 20 Mar 1992


The race to get new biotech products to the market includes the development of biological pesticides and pest-resistant crops. However, pests continually evolve and tend to develop immunity against the new cures. This seems to be already the case with the bacterium Bacillus thuringiensis (Bt) which produces a toxin that kills harmful insects, and on which researchers have put their hopes for a chemical-free agriculture. This article looks at the background, points to the narrow focus of research and warns that, if current trends prevail, another promise of the new biotechnologies might prove to be an empty one.


Bacillus thuringiensis (Bt) is a bacterium which normally lives in the soil. It produces toxins which kill the larvae of moths and butterflies, and almost nothing else. That, and the fact that it is a "natural" product, make Bt an almost perfect pesticide. Organic farmers have recognized this since the beginning of this century, and use this bacterium in their farming systems. But now the giant biotechnology companies, whose main interests are often in selling pesticides, are jumping onto the bandwagon. Using genetic engineering they plan to spread this "miracle cure" throughout agricultural production. However, the cure might be rendered ineffective even before the companies manage to bring it to the marketplace: as insects find their way around the single-gene solutions of biotechnology, more and more reports of resistance against Bt are appearing.

Current research efforts to genetically engineer crops with genes which fight off attacking pests, have always been heralded by the chemical industry as the new tool for an agriculture without chemicals. Back in the 1980s, Sam Dryden of Agrigenetics Company, exclaimed that "in two decades we won 't be spraying crap on plants any more". Since then, many companies have dived into biotech research not only to make that possible, but also to grasp a part of the market share which according to some optimistic analysts could be worth around $US 1 billion by the year 2000. Companies involved in the race include giants such as Monsanto, Sandoz, Lubrizol, NOVO-Nordisk and ICI, and also specialized biotech companies such as Plant Genetic Systems, Mycogen and Calgene.

Most of the work has been focusing on the toxin produced by the Bt bacterium, and different strategies are used to get it to work. One is to engineer genetically Bt for higher toxicity to insects and then to spray it directly on the crop. Another is to incorporate the gene into yeasts in order to obtain large quantities of the toxin through fermentation which can then be incorporated into sprays. Yet another is to plug the Bt gene responsible for the production of the toxin into other bacteria which normally infect the roots of plants, thus protecting these crops against insects which attack the root system. Finally, work is under way to incorporate the Bt genes directly into plants so that agricultural crops can fight off the insects themselves. According to the OECD, between 1988 and 1989, twenty five field releases with such transgenic tobacco, tomato and cotton plants took place in countries such as the US, Israel and Spain. The companies which participated in these experiments were Rohm & Haas, Monsanto, Sandoz, Plant Genetic Systems, Agrigenetics, Agracetus, Calgene and Northrup King.

Developing resistance

Until recently it was thought that insects have difficulties evolving resistance against Bt. After all, organic farmers have been using it for decades without any problems, and researchers were confident that resistance to the toxin would never evolve. They were wrong. In 1985 Dr. William McGaughey of the US Grain Research Laboratory reported that resistance against Bt of the Indian Meal Moth increased thirty-fold in just two generations. In 1986, researchers at the University of Hawaii reported that they had found Bt-resistance in diamondback moths, whose larvae infest watercress, cabbages and other vegetables. According to researchers at the Cornell University in the USA, Bt resistance is also found among the potato attacking Colorado beetles in Florida and New York. Researchers from the US Plant Genetics Institute have already found several other insect species which develop resistance to the Bt protein and research by Monsanto points in the same direction. Other reports indicate Bt-resistant insects on crops in Japan, the Philippines, Thailand and Taiwan. In all these cases, the Bt products were applied to crops in massive amounts similar to the procedure for normal chemical pesticides.

The main reason why Bt resistance is now breaking down even though farmers have used it successfully for many decades is that by repeated blanket applications of the Bt toxin, whether as a spray or by incorporating into crops, researchers are promoting the selection of resistant individuals amongst the insect population. In 1989, The Ecological Society of America issued an authoritative report on genetic engineering and, relating to Bt, warned that both the genetically engineered crops and the unaltered bacteria themselves could be rendered ineffective by creating such conditions which accelerate the evolution of resistance against Bt. The massive dissemination of the Bt gene or of the Bt toxin itself using biotechnology is certainly contributing to these conditions. And this is not the only problem. The extensive use of Bt and other biotoxins could also cause a dramatic change in insect population dynamics which could disrupt the natural balance in ecosystems. Already some Bt strains have been found which are detrimental to beneficial earthworms. Another hazard might consist of the transfer of Bt-genes from genetically engineered plants and microbes to weeds, making them less susceptible to their natural enemies.

Uniformity as a cure?

The main problem lies perhaps in the technology itself. The resistance which biotechnology might breed into crops in the near future will be based on just one or a few genes. The manipulation of entire gene complexes is still far too difficult to handle. Ed Dart, Research Director with ICI Seeds, thinks that crops with single gene traits such as insect resistance are likely to become seed company standards during the coming decade. This "one-gene/one-pest" resistance is relatively easy to overcome by pests, which are continuously adapting themselves to new situations. Just as pests can develop resistance to pesticides, they are also able to find a way around pest resistance in crops, especially when this resistance is provided by only one gene.

Current biotech research is heavily focused on an extremely narrow range of organisms and genes in the search for new instruments to combat pests and diseases. The accompanying graph shows a breakdown of research reports on biological control agents as listed in Derwent Biotechnology Abstracts in 1989. The work on the bacteria Bt is a case in point. This microbe and its "miracle gene" is covered in over 37% of all research papers on biological control agents listed by Derwent in 1989. Another 6% of the papers report on other Bacillus species, while another 10% focuses on Pseudomonas. Taken together, these data suggest that over half of all listed biotech research on biological control agents focus on only two bacterial genera. And even this is probably an underestimate. The Derwent Abstracts, which scan published information sources, tend to under-represent the research in the private sector due to its secrecy. The private sector is likely to focus more strongly on those applications with clear commercial possibilities, of which Bt is the most important one. Bt products are, after all, responsible for 95% of all current biopesticide sales.

Whatever is the research strategy, the "cure" is often the same: Bt's "killer-gene" and the protein which it produces. Here lies exactly the danger of the cure. With research efforts so much directed towards a single microbe, and a specific toxin of that microbe, farmers using the new crops with Bt genes in it might soon face the old problems again. Entomologist Fred Gould puts it this way: "If pesticidal plants are developed and used in a way that leads to rapid pest adaptation, the efficacy of these plants will be lost and agriculture will be pushed back to reliance on conventional pesticides with their inherent problem". For the companies that is not necessarily a problem: if the Bt approach becomes useless they still have the good old chemicals on the shelves to offer.

All this is not to say that the use of biotechnology to produce pest resistant crops or "bio-pesticides" cannot be beneficial to the farmer and to agriculture in general. We desperately need an agriculture which uses fewer harmful chemicals and other external inputs. The question is whether the current reductionist biotech pest control approach, almost entirely focusing on a limited number of single genes, is one which will help to solve the problems. The view of the biotechnologist is narrow in the sense that it focuses on solutions at the molecular level only. It is also narrow in the sense that most biotech research is dictated by commercial interests. This normally means that the sought-after solutions must have a global character: large companies do not tend to work for small market niches, but aim at large market shares. The molecular mind together with the global market share narrows down the focus.

If current biotechnology research programmes do not take seriously the mounting evidence about the emerging resistance to Bt, we run the risk of loosing yet another item from the long list of biotechnology promises. It is likely to bring us from the chemical treadmill onto a biological one, where each time another toxic biological substance has to be found to fight of pests. If that proves not to work, we will be back on the chemical treadmill again. Lost from the sight in the multi-million battle to get biotechnology products to the market, are the organic farmers who have been integrating Bt in their farming systems for decades. If the uniform biotech solutions cause increased occurrence of Bt-resistant insect strains, those farmers will also witness a breaking down of their farming systems which have functioned well for so long.

This article is largely based on a paper by Piet Schenkelaars: "Resistance against Bacillus thuringiensis", In: Clearing House on Biotechnology, Mail-out No. 11. CEAT, Brussels, February 1992. Also used were:

-- Henk Hobbelink, "Biotechnology and the future of world agriculture", Zed Books, London 1991.

-- "Leaflet", Vol 1, Issue 1, HDRA, Coventry, Winter 1992

-- "Microbial Insecticides, special focus on Bt", Rafi Communique, Pittsboro, January 1989.

Author: GRAIN