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dote and rumor from genuine trends." The second, scientific sort of monitoring was the major focus of the workshop. “We are talking about more than just waiting for things to appear; we are talking about a proactive monitoring regimen,” said Barbara Schaal, of Washington University.

Is this sort of monitoring of genetically engineered crops necessary? After all, it is more difficult to carry out, requires a more sustained effort, and demands a higher level of scientific sophistication than simply acting as a sentinel. If it is necessary, why? What should it be looking for? The workshop participants were asked first to address these basic issues. They found the third question perhaps the easiest to answer because there is already widespread agreement in the field as to what sorts of effects might be expected to accompany the cultivation of transgenic crops.

For Bt corn and other crops that have been genetically modified to produce a pesticide, one of the biggest concerns is that widespread use of the crop could lead to the evolution of pests that are resistant to the pesticide. That is of particular concern for organic farmers, said Mark Lipson, of the Organic Farming Research Foundation, because they use the Bacillus thuringiensis (Bt) bacterium as a natural pesticide. For reasons that are not understood, the bacteria produce a variety of substances that are toxic to caterpillars and many other insects, so dusting with Bt allows organic farmers to protect their fields without using chemical pesticides.

A second concern is that crop plants that have been genetically modified to resist herbicides could turn into hard-to-control weeds in succeeding years when their fields are devoted to other crops. “Some of these volunteers can be quite serious,” said Peter Day, of Rutgers University, using the term—volunteer—that agricultural scientists use to refer to crop plants that establish themselves without human intervention. “Volunteer potatoes are sometimes a nuisance in succeeding cereal crops, for example, and might have to be dealt with by herbicide treatment.”

Both risks are expected to affect mainly farmers. Being resistant to a pesticide is not likely to make a difference in an insect's survival away from a farm, where pesticides are not used. Similarly, crop plants that have been genetically engineered to be resistant to herbicides would be no more likely than nonresistant plants to invade the areas surrounding the farm. But transgenic crops might affect ecosystems away from the farm in various ways, and these must be watched for as well.

One example is the possibility that Bt toxin in the drifting pollen of transgenic corn is killing monarch caterpillars. That is a case of what researchers refer to as "effects on nontarget organisms." Of course, chemical pesticides might also kill nontarget organisms and can drift from farmers' fields, but the development of plants that produce toxic pollen is a new phenomenon in agriculture.

Another concern about transgenic plants centers on horizontal gene-

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