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Environmental Effects of Transgenic Plants: The Scope and Adequacy of Regulation
Another argument (used by APHIS in these determinations) is that the “lack of reported incidences” is evidence that something has not happened. For example, the determination for CBH-351 mentioned that increased weediness of corn due to an insect resistance trait has not been reported, as far as APHIS is aware. The committee agrees that if a phenomenon is dramatic and occurs over a short time period, it is likely to be noticed and even reported. That is, a lack of reporting of obvious phenomena may be a strong indicator that such phenomena have not occurred. However, a slight increase in fitness due to insect resistance is an invisible phenomenon, and any increase in weediness of corn due to that trait would likely be slow and subtle, especially since the conventionally bred traits were only moderately effective in conferring resistance.
To demonstrate that corn volunteers are more common as a result of conventionally bred ECB resistance, one would need a detailed comparison between, for example, the incidence of volunteer corn in the 1940s and the 1990s, including a way to isolate the resistance mechanism from other changes in corn production and management. Such an approach could be used to test for environmental effects of pest resistance factors. However, because a “lack of evidence” is used to conclude that there are no effects, there is no encouragement for such testing in the APHIS determinations. In general, use of the term “lack of evidence” can mean anything from “detailed, replicated, long-term experimental studies found no evidence” to “there are reasons to expect a problem but no one has tested this so there is a lack of evidence.”
Finally, the committee found the argument that insect resistance cannot release a plant from ecological constraints to be both weak and inconsistent. Indeed, APHIS is the federal agency that evaluates and approves biological control applications for the importation of insects (including Lepidoptera) specifically to increase herbivore pressure and thereby reduce the incidence of certain weeds. The embedded assumption in the biological control of weeds is that the presence or absence of herbivory, by even one species, can determine whether a plant species behaves as a weed. Biological control was not mentioned in either environmental assessment. A stronger argument for why Lepidopteran resistance would not release corn volunteers would have included an explanation of why corn and its Lepidopteran herbivores are different from those plant-herbivore pairs that result in biological control of weeds. (APHIS cited Gould  as saying that corn is incapable of sustained reproduction in feral populations.)
Impacts on Free-Living Relatives of Corn Arising from Interbreeding. APHIS considered the potential for gene flow from Event 176 transgenic corn and, should it occur, two of its possible consequences. Those conse-