Genetically Modified Crops and the Agroecosystem: Comments on "Genetically Modified Crops: Risks and Promise" by Gordon Conway

David Pimentel

• Abstract
• Benefits of Biotechnology
• Risks of Biotechnology
• Responses to this Article
• Literature Cited

KEY WORDS: Bacillus thuringiensis (B.t.), GM crops, agriculture, biotechnology, economics, ecosystems, genetic engineering, herbicides.

Published: March 27, 2000

Dr. Gordon Conway's timely address to Monsanto, published in Conservation Ecology (Conway 2000), provides a sound perspective of the promise and risks of genetically modified crops. This commentary serves to supplement his paper, and focuses primarily on genetically modified crops, or biotechnology in agroecosystems.

According to the World Health Organization (WHO 1996), more than 3 billion humans are currently malnourished worldwide. Conway reports that only 800 million people are undernourished, but he does not indicate that this number represents only people who are calorie-malnourished. The WHO estimate of 3 billion malnourished includes people who are calorie-, protein-, vitamin-, iron-, and iodine-malnourished. As the human population continues to increase, the number of malnourished could conceivably reach more than 5 billion in future decades.

Several recent facts provide evidence for this trend of increasing numbers of malnourished humans worldwide. For instance, the Food and Agricultural Organization states that per capita availability of world cereal grains, which make up 80-90% of the world's food supply, has been declining since 1983 (FAO 1998). Per capita declines during the past decade in cropland (20%), irrigation (15%), fertilizers (23%), and fish production (10%) contribute to this decline in global food availability (Pimentel et al. 1999).

Conway has confidence that biotechnology will help to increase crop production in the future. Some of the technologies currently being developed certainly will increase crop production and benefit agroecosystems. For instance, transferring Bacillus thuringiensis (B.t.) toxin into some crop plants will help to control some caterpillar pests, such as the European corn borer. Other opportunities also exist to incorporate some of the thousands of pest-resistant factors naturally occurring in plants to crops for control of serious insect and mite pests. Adding resistant factors to crop plants will reduce our reliance on some toxic insecticides and miticides. Genetic engineering enables scientists to utilize a wide array of resistant factors and incorporate them into crops in half of the time needed in classical plant breeding (Paoletti and Pimentel 1996).

Similarly, transferring resistant factors to crop plants could help to control plant pathogens. Some plant pathogens are already controlled by host plant resistance, but by using biotechnology, a great many more resistant factors obtained from natural plant species could be incorporated into crop plants to aid in plant pathogen control.

The ability to improve the nutritional quality of food crops is another potential benefit of biotechnology. For example, it should be possible to improve the quality and quantity of essential amino acids, vitamins, and microminerals in food crops. Such improvements in food quality could help to reduce the number of people who are malnourished (Guerinot 2000).

In addition, it is important to consider that the major cereal crops of the world are annuals. If, by genetic engineering, annual grains could be converted into perennial grains, then tillage and soil erosion could be reduced and nutrients could be conserved in perennial crops. Use of these perennial crops would decrease labor, improve labor allocation, and, overall, improve the sustainability of future agriculture. Also, energy efficiency in the cultivation of perennial cereal crops would be greatly superior to the efficiency of annual crop production.

One of the ultimate aims of genetic engineering is to develop cereal crops that are able to provide their own nitrogen by bacterial symbiosis, similar to leguminous plants. Achieving this goal would reduce the large amount of energy used to produce and apply nitrogen fertilizers, and would also reduce the costs of production. There is growing evidence that this goal eventually may be realized through genetic engineering, similar to the improvement of inoculation processes with rice.

The previous examples suggest some of the potential benefits that biotechnology can contribute to agriculture and agroecosystems. However, some genetically modified crop technologies have potential risks to agroecosystems. For example, the use of herbicide-tolerant crops encourages the heavy use of herbicides in the crop field without damage to the crop. At present, breeding crops for herbicide tolerance dominates about 41% of the research on genetically engineered organisms. Herbicide tolerance does not increase crop yields, but it does increase the use of herbicides in agriculture and the pollution of agroecosystems and other ecosystems. The use of herbicide-tolerant crops also has doubled the costs of weed control in some crops (Pimentel and Ali 1998).

Growing crops requires enormous amounts of water. Approximately 5 million liters of water are required to produce a hectare of corn. Conway indicated that it will be possible to make crops "highly drought-tolerant." Given that such large quantities of water are vital to the photosynthesis of crop plants, this prediction is highly questionable. The best estimates suggest that water use in crop production could be reduced by about 5%, but not to the extent that they would be highly drought-tolerant (Paoletti and Pimentel 1996).

Because engineered organisms bear alien genes that could potentially be transferred to wild relatives, there is justifiable concern that the alien genes of genetically engineered plants could move to other plants and upset not only the agroecosystem but also other ecosystems. For example, major weed species have originated from hybridization with crop plants, such as crosses of Brassica camprestris (weedy relative) with B. napus (oilseed rape), and Sorghum halepense (Johnson grass) with S. bicolor (sorghum corn) (Paoletti and Pimentel 1996). Proponents of genetic engineering rely on the experience with corn hybrids and other genetically altered crops that have not caused in any major environmental problems to support continued development of genetic engineering. Nonetheless, most important for the success of biotechnology are the basic questions of how to evaluate every genetically engineered organism before its release to insure its safety for the environment.

As Conway mentions, sometimes the release of genetically engineered crops has been rushed to get these crops to farmers. This appears to be the case with B.t.-engineered corn. The pollen from B.t. corn has been confirmed to be toxic to the remarkable monarch butterfly (Losey et al. 1999), already threatened by habitat loss at its Mexican wintering sites. The B.t. corn is aimed at control of the European corn borer, a relatively minor pest in corn when compared with the corn rootworm complex. The rootworm is the major pest in corn; more than 95% of the insecticide applied to corn is applied for the control of this pest complex. It is hoped that corn can be genetically engineered to control the corn rootworm complex.

These examples illustrate that GM technology can be better managed to benefit agriculture while reducing the risks to environment (Pimentel and Raven 1999). However, another problem related to biotechnology in agriculture has been the incorporation of alien genes into crops from plants to which people have allergies. For example, adding genes from some nut genotypes into soybeans has made some people with allergies quite ill (Paoletti and Pimentel 1996).

Genetically engineered crops offer opportunities to improve the environment by reducing the need for and use of chemical pesticides, developing perennial grains, slowing soil erosion by using perennial crops, increasing crop yields, and improving the nutritional quality of crops. On the other hand, several aspects of biotechnology have negative impacts on agroecosystems. These include herbicide-resistant/tolerant crops, some B.t. crops, the incorporation of genes to which some people are allergic, and the transfer of modified genetic material into weeds and other wild plant relatives. However, with careful investigation and field testing before release of modified plants, we can look forward to biotechnology’s positive contributions to agroecosystems and world food supplies. The FDA, EPA, and USDA need to establish a rigorous set of standards, like those that exist for pesticides, for testing GM crops and livestock before release to the public. In addition, all GM foods should be labeled so that the public can make informed decisions about the products they use and purchase.

Responses to this article are invited. If accepted for publication, your response will be hyperlinked to the article. To submit a comment, follow this link. To read comments already accepted, follow this link.

Conway, G. 2000. Genetically modified crops: risks and promise. Conservation Ecology 4(1): 2. [online] URL: http://www.consecol.org/vol4/iss1/art2/

FAO. 1998. Food balance sheets. Food and Agriculture Organization of the United Nations, Rome, Italy.

Guerinot, M. L. 2000. The green revolution strikes gold. Science 287: 241-243.

Losey, J. E., L. S. Rayor, and M. E. Carter. 1999. Transgenic pollen harms monarch larvae. Nature (20 May) 399: 214.

Paoletti, M. G., and D. Pimentel. 1996. Genetic engineering in agriculture and the environment. BioScience 46(9): 665-673.

Pimentel, D., and M. S. Ali. 1998. An economic and environmental assessment of herbicide-resistant and insect/pest-resistant crops. Indian Journal of Applied Economics 7(2): 241-252.

Pimentel, D., and P. Raven. 1999. Commentary: Increase in genetic engineering means less reliance on chemicals. St. Louis Post-Dispatch, 1 August1999: B3.

Pimentel, D., O. Bailey, P. Kim, E. Mullaney, J. Calabrese, L. Walman, F. Nelson, and X. Yao. 1999. Will limits of the earth’s resources control human numbers? Environment, Development, and Sustainability 1(1): 19-39.

WHO. 1996. Micronutrient malnutrition: half the world’s population affected. World Health Organization, Number 78, 13 November 1996:1-4.