GMOs:Tree Hackers, Bathwater, and the Free Lunch
Any scientific discipline worthy of the name has robust theories to explain the phenomena in its purview; I count at least three in ecology. The first two, the theory of evolution by natural selection and the theory of island biogeography, explain ecological phenomena and are also useful, helping us to manage antibiotic and pesticide resistance and to design ecological preserves. The third manifests itself in any system in which resources are limiting: It is the theory of the free lunch.
The human population exceeds 6 billion souls, and counting. Each of us expects a sustaining share of food and fiber, courtesy of the applied ecological disciplines of agriculture, forestry, and fisheries. We run hard to stay in place, feeding and clothing most of us—for the time being—despite peaking crop yields, declining fish catches, steady losses of irrigation water to development and industry, and diversion of calories to meat production as increasing affluence enables more of us to ascend the food chain.
Insects, weeds, and plant pathogens take about 40% of food and fiber production worldwide (David Pimentel, Techniques for Reducing Pesticide Use: Economic and Environmental Benefits, Chichester [UK]: John Wiley and Sons, 1997); it would be worse if we didn't take steps to control them. Weeds can be controlled by mechanical cultivation, but that promotes soil erosion and requires burning fossil fuels, which depletes finite resources and contributes to greenhouse warming. Increasingly, all classes of pests, including weeds, are controlled by chemical pesticides, which endanger the health of humans, livestock, and wildlife and reduce populations of natural enemies that can help to suppress pest populations. Even narrow-spectrum pesticides may be problematic (see the Forum article by Stark and Banks in this issue).
A new tactic is the introduction of pest-fighting genes into plants. As reported by Tabashnik and Ortman and their colleagues (see Letters to the Editor, this issue), this approach has dramatically reduced chemical insecticide use in cotton and corn. As a bonus, natural enemy populations rebound, exerting pest control and concomitantly reeducating growers—the ultimate decisionmakers in pest management—about the value of these allies.
The deployment of genetically modified crops has also had adverse consequences. The canary in this particular coalmine is the monarch butterfly, whose larvae are killed or stunted by consumption of pollen expressing the Bt toxin, which confers the plants' pesticidal properties. Whether or not the impact on monarch populations has been overstated (see Obrycki's response to Ortman and colleagues in this issue), it demonstrates that genetic engineers must tailor the expression of genes to avoid unwanted impacts on nontarget species.
Last March, a band of self-declared protectors of the planet damaged 960 experimental trees planted by the Tree Genetic Engineering Research Cooperative at Oregon State University. Among TGERC's goals are to spare large tracts of native trees by increasing productivity of short-rotation tree plantations and to prevent the spread of genes from plantations to wild populations by engineering nonflowering trees. The zealots who harmed TGERC's trees are untroubled by such considerations; they want the free lunch, to have a Green World where humankind lives lightly off the bounty of a benign and unmanipulated Nature.
But ecology's third theory is rock solid, and if we do not stay ahead of pests with the cleverest methods we can devise, the Third Horseman, whose province is agriculture, will take up the slack. Sustainable deployment of genetically modified organisms will require the highest discipline and intelligence. Some of the bathwater should be thrown out, but we dispose of the baby at our peril.