Many critics believe we're opening a Pandora's lunchbox with GM technology, that raising GM crops is an uncontrolled experiment with unknown consequences for surrounding ecosystems. Remember, they admonish, the ravages of the now-banned pesticide DDT. Or PCBs. Or dioxin. Or leaded gas.

One of their greatest worries is that GM crops could harm other wildlife. A 1999 article in Nature about detrimental effects on monarch butterflies stoked that fear. Cornell University researchers found that only 56 percent of monarch larvae survived when fed milkweed plants covered in GM corn pollen, whereas all those fed milkweed leaves with traditional corn pollen lived. About half of monarchs in the U.S. spend their summers dining on milkweed in corn-growing regions, so to environmental activists this proved dire news.

GM defenders point out that the monarch study was held in a laboratory, not in the field, and that follow-up studies by the Department of Agriculture, Food and Drug Administration, and others suggest the original study may have been flawed. But those concerned about the study say that, at the least, it should serve as a cautionary tale for those who dread unwittingly harming species.

Citing the case of mosquitoes that became tolerant of DDT, critics also shudder at the thought that insects will become 'superbugs' resistant to pesticides engineered into GM crops. By the same token, they also predict the evolution of 'superweeds' that become immune to a broad-spectrum weed killer after crossing with and assuming the herbicide-resistant gene from a closely related GM plant. GM crops themselves can become weeds, they note. Canadian farmers have reported that herbicide-resistant canola plants have invaded nearby wheat fields with the impunity of a feared superweed.

Naysayers also worry that viruses will snatch resistance traits from GM crops bearing genes from crop viruses. These gene-thieving viruses might then evolve into entirely new strains that could infect a whole range of plants previously unaffected.

"Unrelated multiple side-effects of introduced genes cannot be predicted in advance and are not always visible or easily detected."

--Dr. Ricarda Steinbrecher, Women's Environmental Network, London, U.K. [13]

"[Genes jumping to wild relatives, possibly leading to 'superweeds'] could be particularly significant in countries where crops have weedy relatives. In the USA, where many of the transgenic crops are being forged, there are no weedy relatives of soya beans, maize, wheat, or cotton. Weedy relatives of these crops, however, exist in other regions where the genetically modified crops are targeted, including Central America, Asia, and the Middle East."

--Topsy Jewell, Pesticide Action Network U.K. (formerly Pesticides Trust), London, U.K. [14]

"Ecologists are unsure of the impacts of bypassing natural species boundaries. Consider, for example, the ambitious plans to engineer transgenic plants to serve as pharmaceutical factories for the production of chemicals and drugs. Foraging animals, seed-eating birds, and soil insects will be exposed to a range of genetically engineered drugs, vaccines, industrial enzymes, plastics, and hundreds of other foreign substances for the first time, with untold consequences."

--Jeremy Rifkin, author of The Biotech Century: Harnessing the Gene and Remaking the World [15]

References:
13: Quoted in "Greed or Need? Genetically Modified Crops," www.oneworld.org/panos/briefing/brief30.htm.
14: Ibid.
15: "Unknown Risks of Genetically Engineered Crops," op-ed piece in The Boston Globe, 6/7/99.

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