Monsanto, the biggest marketer of Bt crops, does not foresee any need for strengthening existing protective measures nor for federal regulation of resistance-management plans. Officials cite the company's mandate that farmers should establish refuges for Bt corn and potatoes, even in the absence of an EPA requirement. Eric Sachs, business director for YieldGard, the company's Bt corn product, says scientists who demand larger refuges fail to take into account the potential for improving genetically engineered crops. One way for insects to develop resistance is by altering receptors in the gut where the toxins bind. Even these approaches may not be foolproof.
Pests can also develop new mechanisms of resistance.
Brenda K. Oppert and William H. McGaughey, along with other U.S. Department of Agriculture researchers, reported in the Journal of Biological Chemistry in September that one pest, the Indianmeal moth, can become resistant if it lacks a key enzyme, a proteinase, that is needed to activate Bt toxins. Over time, biopesticides that serve as alternatives to Bt crops may be needed. Just a few cells of Photorhabdus luminescens can kill some insect pests. A bacterial enzyme has the unusual property of making the dying insect glow blue, perhaps to scare off mammalian predators. Dow AgroSciences is now trying to insert the cloned genes into a variety of plants, which can then produce their own pesticide.