Genetically modified crops for insecticide resistance: Are the benefits worth the risk?
Dr. Robert W. Jones March 8, 2010.
Professor, Faculty of Natural Sciences, Autonomous University of Queretaro, Mexico
Email: rjones@uaq.mx
The publication of the book, Silent Spring, by Rachel Carson in 1962, is generally considered the seminal event in the initiation of the environmental movement. The arguments of the book linked the use of synthetic chemicals for the control of insect pests with other biological phenomena being witnessed at the time. She succinctly explained how with indiscriminate use, DDT entered the food chain and accumulated in the fatty tissues of animals, including human beings, and was linked with genetic and neurological problems. The extremely high residual action of DDT meant that the chemical persisted in the environment for many years, and Carson concluded that DDT and other pesticides had irrevocably harmed birds and animals and had contaminated the entire world food supply. Despite vehement opposition to the book, especially from the agrochemical industries, a special commission was assigned to assess the problem in 1963, by the then, president of the United States, John F. Kennedy. After examining the issues raised by the book, the commission strongly supported the conclusions of Carson, and vindicated both Silent Spring and its author.
Silent Spring not only revealed the consequences of the indiscriminant release of synthetic chemicals into the environment, it also inflamed a growing distrust in the philosophical tenets of modern life of the 1960’s. No longer was there a general belief that science would be able to solve our problems, and there was a growing awareness that continued improvement in the quality of life through technological advances was perhaps not a certainty. This shift in the public mind set was, of course, part and parcel of the social upheaval and fervent criticisms of the status quo that characterized of the times. But Rachel Carson’s little book had scientific validity and could not be swept aside as a passing fad.
The changes resulting from the publication of Silent Spring and the environmental movement that it spawned were significant. The first country to ban DDT was Hungary (1968), then Norway (1970), Sweden (1970), and the United States (1972). Many countries followed suit and DDT has been banned in many countries, (although continues to be used in the public health sector for malaria control). Other highly toxic or high residual pesticides such as lindane, toxaphene were also banned from the farmer’s chemical armaments in the 1970’s and 80’s. Additional changes included greater restrictions on the use of approved pesticides through stricter labeling and regulations of sale. The licensing procedures and restrictions for newly developed chemical pesticides increased enormously such that the costs and complexity of getting a new insecticide on the market became exceedingly expensive. Importantly, the science of integrated pest management (IPM) arose out of the need to reduce reliance on chemicals as the sole means of reducing losses to pests. The philosophy of IPM was to use as many tactics as possible in managing pests, and only using pesticides when economic damage to crops was a certainly. Despite these advances, pesticides continue to be widely used with global pesticide use estimated at 5.5 billion pounds for 2000 (EPA 2009) with annual total economic and environmental costs calculated at up to $8 billion (Pimentel et al. 1992).
So where do we stand today and what is the legacy of Rachael Carson and her little book in the 21st century? Certainly many advances have been made in the science of IPM and in the knowledge and legislation related to pesticide use. Unfortunately, in many parts of the world, IPM programs never really got off the ground, and chemical control remains synonymous with the concept of modern insect control practices. For example in Mexico, although there are important regulations to control and specify chemical control practices, there is little enforcement of the regulations concerning the legal restrictions of use of which chemicals are used on what crops and when (personal observation). The important advances in integrated pest management seen in other countries have not made much head way in Mexico. This is apparently the general situation in much of the lesser developed world.
One would think that with the high economic and environmental costs associated with the use of insecticides that alternative technologies to reduce losses to pest organisms would be welcome. This should be the case. But the public has apparently wearied of debate surrounding insecticide use, and moved onto new causes, and by implication, have now accepted the environmental costs of insecticide use. One of these new causes is opposition to genetically modified crop varieties (GM). I will not argue the costs and benefits of all the new types of GM crops, and only focus on one new innovation in the transgenic world, the so-called Bt crops.
Transgenic Bt crops, have a gene from the bacteria Bacillus thuringiensis for producing a protein that is toxic to specific orders of insects, depending on the strain of bacteria. The insecticidal properties of this gene were well known for many years, as formulations of the bacteria were sold as a “natural” insecticide as early as 1948 and are actually approved as a biological control tactic for organic farming (Glare and O’Callaghan 2000). Presently, the majority of Bt transgenic crops have a protein that are toxic to Lepidoptera. Thus, a lepidopteran larvae feeding on a plant with the Bt gene, is usually dead within a few days and the pest population never develops. This Bt protein does not affect insect parasites, nor predators so the use of Bt transgenic crops is compatible with biological control programs for other non lepdopteran pests. The toxicity of the commercial formulations of Bt protein are classified as “nontoxic” (LD50 > 5000 mg/kg oral rat) and few physical reactions to the protein in humans have been reported (Ware 1989).
All new technologies carry a risk, especially biological materials released into the environment; this is the lesson of Rachel Carson. We are obligated to acknowledge the risk of releasing Bt crops into the environment, but we must also weigh the costs and benefits of Bt crops with the present agricultural practices and attempt to choose the best alternative. There are two important and acknowledged problems for the use of Bt crops for insect control: 1) development of resistance of pests to the Bt gene, and 2) the contamination of wild hosts through gene transfer to wild populations. The development of resistance to the Bt protein is a clear threat, because insects are constantly in contact with the Bt toxin and resistance has been verified for several pest insects (Gahen et al. 2001, Morin et al. 2003) . However, because of its unique specificity, the development of resistance to Bt appears to be limited only to this specific insect toxin, and the consequences are that Bt would be rendered ineffective as an insect management tool. This would be an important loss as a management tool for lepidopteran, but presently, the Bt gene remains effective as a lepidopteran pest deterrent in the majority of the regions where these crops are planted (Fox 2003)
The second and more general concern is the escape of the gene for the Bt gene into the genome of wild plants. This is of serious concern where native species and varieties exist, and must be evaluated. However, if concerns are that wild varieties will incorporate these foreign genes and somehow their “wildness” contaminated, it should be noted that this has always been a problem. Commercial varieties with many foreign genes from diverse geographic and races and species have been in close contact and threatening the integrity of native crop plants since the domestication of plants. It would seem a more efficient and direct method of addressing this problem would be to establish programs for native crop conservation. For example, Mexico is one of the geographic centers of the domestication of cotton (Stephens 1972), and 13 species of Gossypium are presently recorded for the country (Fryxell 1979). Although there are important initiatives for the conservation of native varieties and wild species of cotton in Mexico, including the “Red de Recursos Genéticos de Gossypium ssp en México” and programs within the Instituto Nacional de Investigaciones Agrícolas, Forestales y Pecuarias (INIFAP), (Beltrán Rodríguez 2010), presently this author knows of no concerted program or national plan to conserve, in situ or ex situ, species and/or varieties of Mexican cottons. In other words, there may be no point in the ban of Bt cottons for Mexico in the future, simply because the native wild cottons may cease to exist.
So how do these principal risks of Bt crops compare with their benefits. Presently, Bt crops are grown on approximately 43 million hectares in the world (James 2007), of which 40% are in developing countries (Fitt 2008). In general, use of Bt crops have significantly reduced insecticide use in regions where they have been planted. In cotton, a crop with heavy insecticide usage, Brookes and Barefoot (2006) estimate that the volume of the insecticide active ingredient (a.i.) was reduced by 94.5 million tons in ten years of Bt crop use. In percentages, the reduction in insecticide use is approximately 50% in Bt cotton compared to non Bt cotton worldwide (Fitt 2008). Reductions in insecticide use in corn is not as dramatic, but still estimated at 12.5% less insecticides for the United States in 2005 (Fit 2008). Notable benefits for subsistence agriculture in Africa are also reported by Gouse et al. (2006) with the use of these varieties. Other GM crops with the Bt gene have also recorded significant reductions in the use of insecticides, although the area planted to these are much less when compared to cotton and corn. Fitt (2008) notes the benefits of Bt crops extend beyond the reduction of insecticides, because they are compatible with other pest management tactics, especially biological control.
The evaluation of risk is a personal and political decision. Personally, I am strongly in favor of the use of Bt crops for the potential in reduction in insecticides. For me, it is no contest. Even if the reduction of insecticides was in the range of 5-10%, I would still be strongly in favor of accepting the risks of Bt crops over the well documented, and serious risks of insecticide use. How can we not celebrate that 94.5 million tons of biocides were not liberated into the environment. If the critics of GM crops are really concerned with the environment, then also must seriously consider the alternative of not using Bt crops. It is part of society’s cultural maturation that we heed the warnings of Rachel Carson; we must evaluate new technological developments and not simply trust scientists and politicians. But we must also be wary of an overreaction, as well. In the protests over GM crops, we are throwing out the proverbial baby in the bathwater, and forgetting the roots of the environmental movement. Rachel Carson’s arguments against the use of DDT had teeth because they were based on scientific evidence and not cultural fashion or political motives. Looking at the evidence, insecticides, even in limited use, pose a much greater threat to the environment than GM crops.
Literature cited
Beltrán Rodríguez, L. A. 2010. El algodón (Gossypium ssp.) en Mesoamérica: conservando el recurso y preservando el conocimiento, Hypatia 2010 32:
Carson, R. 1962. Silent Spring, Houghton Mifflin, New York
Environmental Protection Agency (EPA). 2009. The value of countries working together to regulate pesticides and food safety. EPA-735-K09001, Washington, D. C.
Fitt, G. P. 2008. Chapter 11. Have Bt Crops led to changes in insecticide use patterns and impacted IPM?. In. Romeis, J., A. M. Shelton and G. G. Kennedy. Progress in Biological Control. Volume 5. Integration of Insect-Resistant Genetically Modified Crops within IPM Programs. Springer Press, New York
Fox, J. L. 2003. Resistance to Bt toxin surprisingly absent from pests Nature Biotechnology 21: 958 – 959
Fryxell, P. A. 1979. The Natural History of the Cotton Tribe. Texas A&M Univ. Press, College Station, Texas 245 pp.
Gahan L., F. Gould, and D.G. Heckel. 2001. Identification of a Gene Associated with Bt Resistance in Heliothis virescens Science 293: 857-860
Glare, T.R., and O’Callaghan, M.. 2000. Bacillus thuringiensis: Biology, Ecology and Safety. Wiley Press, New York
Gouse, M., pray C., Schimmelpfennig, D. and Kirsten, J. 2006. Three seasons of subsistence insect-resistent maize in South Africa. Have smallholders benefited? AgBioForum 9: 15-22
http://hypatia.morelos.gob.mx/index.php?option=com_content&task=view&id=553&Itemid=488
Morin S., Bigs R., and Sisterson M. 2003. Three cadherin alleles associated with resistance to Bacillus thuringiensis in pink bollworm. PNAS 100: 5004-9.
Pimentel, D., H. Acquay, M. Biltonen, P. Rice, M. Silva, J. Nelson, V. Lipner, S. Giordano, A. Horowitz, and M. D’Amore. 1992. Environmental and economic costs of pesticide use. Bioscience 42: 750-760
Stephans, S. G. 1972. Geographical distribution of cultivated cottons relative to probable centers of domestication in the New World. pp 396-407. In. A. M. Srb [ed.] Genes, enzymes and populations. Plenum Press, New York
Ware, G. 1989. The Pesticide Book, Thompson Publications, Fresno, CA, USA
