Bt or not Bt : Is that the question?

Recent public concerns over the transgenic (genetically modified) plants and nontarget impacts such as those from Bt-toxin expressing corn pollen on the monarch butterfly populations have escalated, despite good pest management intentions and good science (1–9). Plant resistance to insect pests has evolved naturally over many millions of years and involves (i) both constitutive and inducible phytochemical and morphological mechanisms in plants, (ii) counteradaptations to plant defenses by the herbivores, and (iii) biotic interactions of the multitrophic level communities of insect pathogens, parasites, and predators (10–13). The outcomes of such complex biotic interactions are sometimes determined by local mosaics of abiotic environmental conditions or regional climate changes that directly influence the component participants and their behavioral, physiological, and genetic adaptations (14–16). The intentional selection and breeding of insect and/or pathogen-resistant plant genotypes such as corn (Zea mays) has resulted in slow, but steady, progress against stalk-boring larvae such as the European corn borer and other such species, and host plant resistance in general has significantly reduced the need for broad-spectrum insecticides across agroecosystems and forests (17, 18). The use of fairly specific natural microbial insecticides such as the Cry1Ab or Cry 1Ac endotoxins from Bacillus thuringiensis var. kurstaki (Btk) have been hailed as a new jump-shift in targeted pest control methods, with putatively minimal impacts on nontarget organisms in millions of acres of forests for gypsy moth control and cornfields for stalk-boring Lepidoptera control (19, 20). The specificity of Btk (for Lepidoptera) and Bti (for Diptera) has not always been accepted in the public mind. For example, in the 1980s mosquito control sprays with Bti were suspected to be killing nontarget Lepidoptera (including the endangered Schaus swallowtail butterfly) in Munroe County of the Florida Keys (P. Eliazar, personal communication) potentially …