Moderate-dose crops have no place in such a strategy because they tend to cull out the susceptible organisms and leave the population enriched for resistance. They are even more likely to elicit resistance if the resistance traits are dominant or partially dominant as in the case of the research noted above. These include all those based on Event 176 and DBT418, which produce moderate doses during the second generation of corn borers. If the Agency is serious about resistance management, it should not approve Bt crops that unequivocally fail to meet the requirements of the high-dose strategy. The Agency should rescind the registrations for all Bt-corn varieties based on moderate doses for target pests and should establish a policy barring the approval of any such varieties in the future.
Sound science demands no less.
Bt-resistant H. zea would pose an extremely serious problem for many traditional users of Bt spray formulations as well as farmers planting transgenic corn and cotton. Known as the cotton bollworm on cotton and the corn earworm on corn, H. zea is also subject to moderate Bt doses in these crops. Exposure to less-than high doses of Bt toxin in both corn and cotton exacerbates the selection pressure for resistance. EPA approved Bt cotton knowing that it produces only a moderate dose of Bt toxin against H. zea , one of three target cotton pests. As a result, H. zea has relatively little opportunity to evolve resistance to Bt corn, since moths feeding on plantings of Bt corn throughout much of the corn belt do not survive to produce subsequent generations.