arch butterfly larvae were fed milkweed dusted with transgenic Bt pollen, high mortality was exhibited (Losey et al. 1999). The relationship between this preliminary laboratory finding and field effects is unclear (Yoon 1999). One recent field test reports that at least 500 pollen grains per square centimeter is necessary to sicken monarch caterpillars and that milkweed plants growing adjacent to corn fields had only an average of 78 grains per square centimeter (Kendall 1999) (see section 2.6.2). In other experiments, however, monarch caterpillars that consumed concentrations of Bt corn pollen (Event 176) naturally deposited on milkweeds in the field experienced 20% mortality with only 48 hours of exposure (Hansen and Obrycki 1999a,b). Further field-based research is needed to determine whether dispersed Bt pollen could have detectable effects on the population dynamics of nontarget organisms.
The above concerns have led some to question the safety review that transgenic crops receive in the United States under the coordinated framework. Many believe that transgenic crops present substantial human health and ecological risks, and that these are not properly assessed by the regulatory framework. But many others believe that the risks are minimal, that the benefits outweigh the risks, and that the current regulatory scheme is perhaps onerous.
Cited benefits include a reported 250,000-gallon reduction in chemical pesticide use in 1996 and a 30-50% reduction in the number of insecticide applications over the period of 1996-1998 due to the growing of commercial transgenic Bt cotton (Robinson 1998; Williams 1997, 1998, and 1999). The reduction might prevent much environmental damage. In addition, Bt toxins have specific insect targets, whereas traditional broad-spectrum chemical insecticides often kill insects more indiscriminately (Federici 1998). This may lead to outbreaks of secondary pests requiring the use of more insecticides. However, many believe that transgenic pest-protected plants should not only be compared to the use of chemicals, but also to alternative methods such as biological control.
The debate has intensified in recent months, given the international concerns and impending regulatory decisions in the United States. In March 1999, Congress held a hearing on the 1994 proposed EPA plant-pesticide rule (Hart 1999c). Although transgenic pest-protected plants have been registered under this rule in the last 5 years, the rule has not been finalized, and its scientific and legal validity are being questioned. The EPA planned to finalize the rule by the end of 1999. The debate over this rule has many facets. Environmental and consumer groups argue that the EPA is not rigorous enough in its scientific review (Hart 1999c)