Transgenics Gone Wild!

Why it's OK for transgenic plants and animals to spread


"GE Grass Spreads Genetic Pollution over Large Distances" warns the headline in the environmentalist magazine Grist last month. Pollen from a grass genetically modified for herbicide tolerance was found 13 miles from where it was planted. Biotechnology foes have always warned us that genetically modified creatures, once free in the outside world, are beyond our control.

For example, the Sierra Club worries, "These organisms cannot be recalled—they will continue to pass on their spliced-in genes, or transgenes, to future generations. Many of the gene changes may turn out to have unexpected secondary effects. Serious errors in judgment might prove unrecallable as trillions of copies are broadcast via pollen and seed." Sounds ominous, right? However, that genetically modified organisms released into the wild might be unrecallable is not necessarily a knock-down argument against them. After all, lots of unmodified organisms are unrecallable too.

Most transgenics so far allowed outdoors are crop plants genetically enhanced to resist insects and diseases, and to tolerate herbicides. Crop plants have been modified through millennia by farmers so that they simply cannot survive in the wild. You won't see corn plants taking over forests or swamps.

Nevertheless, some genetically modified crop plants have crossbred with wild relatives. But so do conventional crops. Norman Ellstrand, a genetics professor at the University of California at Riverside notes that "there is now substantial evidence that at least 44 cultivated plants mate with one or more wild relatives somewhere in the world…crop-to-wild gene flow is not uncommon, and on occasion, it has caused problems. Would we expect transgenic plants to behave any differently? The answer is 'no.'"

Critics often worry that genes for herbicide resistance from genetically modified crops can flow into weed species, making them more difficult to control. However, this is hardly a novel problem. As professor of plant physiology Jodie Holt, also from Riverside, observes, "As use of herbicides has increased, increased cases of selection for resistance in weeds have been documented. Since the first reported case of weed resistance in 1970, 258 weed species have evolved resistance to one or more of 18 herbicide classes." Despite the fact that for nearly a decade millions of acres have been sown with biotech crops, there have been precious few outbreaks of the much-dreaded "superweeds" caused by crossbreeding between biotech crops and wild plants.

So now some scientists are working on deliberately releasing genetically modified organisms above the plant level into the wild. For example, mosquitoes have been genetically modified so that they can no longer harbor disease-causing organisms, such as the malaria parasite, or viral diseases such as dengue fever and yellow fever. The tropical kissing bugs in Central and South America have been infected with genetically engineered bacteria that kill the Chagas trypanosome parasite that the bugs carry. The trypanosome carried by tsetse flies in Africa that causes sleeping sickness might be controlled in a similar fashion.

Researchers at the University of California at Riverside are trying to stop an epidemic of Pierce's disease that is threatening California's vineyards. The disease bacterium is spread by a leafhopper pest called the glassy-winged sharpshooter. The Riverside scientists have modified another bacterium that lives in the guts of the sharpshooters so that they kill the bacteria that cause Pierce's disease. Other researchers are trying to modify honeybees to resist the diseases and parasites that have devastated huge numbers of hives in the past decade.

This kind of genetic engineering approach is an extension of biological control strategies already in regular use. For example, pink bollworm moths that attack cotton, as well as screwworm flies that infest livestock, are controlled using Sterile Insect Technique (SIT). Male moths and flies made sterile through irradiation are released in huge numbers so that they will out-compete their wild rivals for mating with wild females, whose eggs then produce no progeny. The U.S. Forest Service controls gypsy moth infestations by spraying forests with a preparation of a natural virus that infects and kills only gypsy moths.

Unlike crop plants, which can't typically compete with wild species, researchers hope that genetically modified insect species will successfully out-compete unmodified wild members of their species. Any potential negative effects will have to be balanced against the benefits expected—which can be substantial. For example, at least 300 million people contract malaria and nearly three million people die from it every year. Using interbreeding to replace wild populations of malaria-carrying mosquitoes with mosquitoes genetically modified to resist malaria would be a tremendous boon to humanity.

This process of releasing genetically modified insects and microorganisms to control diseases and pests will undoubtedly be modeled on successful programs like the biological control of the weed purple loosestrife. Biologists imported and released two leaf-feeding beetles and a root-eating weevil from Europe that eat only purple loosestrife. These insects were tested in laboratories before they were released to make sure they would not endanger native North American plants. This effort at biological control has significantly reduced stands of the weed. In a similar fashion, future genetically modified insects will be extensively tested and monitored in the lab before they are released, to minimize any ill effects.

While it is possible that genetically modified plants and animals could become disruptive when introduced into the wild, this risk must be evaluated in light of what we know about the history of introducing unmodified new species into ecosystems. In the 500 years since Columbus arrived in America, some 50,000 foreign species have become established in North America. These include nearly all our major crop plants: wheat, oats, soybeans, apples, oranges, and pears; and our livestock: cows, pigs, goats, sheep, and horses. Of course, some destructive pests have also found their way to our shores, but for the most part introduced species have not been particularly disruptive and have integrated well into our landscapes.

A recent study on the ecological effects of genetically modified trees by researchers at Oregon State University noted, "Invasive exotic organisms represent the coordinated interaction and evolution of thousands of genes in a new environment, usually devoid of its pests and pathogen complex, [whereas] transgenic organisms result from one or a few intensively studied genes that encode highly specific traits."

It is reasonable to expect that creatures like insects modified with just one or two well characterized genes will be less disruptive than introduced exotic species, since their wild relatives will already be living in the ecosystem into which the modified animals are being introduced. If mosquitoes genetically modified to resist malaria or West Nile virus actually succeeded in replacing wild carriers, people would suffer just as many irritating bites from the bloodsucking nuisances. But they'd come down with fewer cases of illness. And returning to transgenic grasses, biotechnologists have now genetically modified popular lawn and pasture grasses so that they lack two common hay-fever allergens. Not even the Sierra Club should sneeze at such positive results.