Researchers have long worried that crop-munching insects could become resistant to Bt, a toxin naturally produced by the microbe Bacillus thuringiensis that is harmless to most other organisms. Bt use is common; crops with the pesticide cover more than 32 million hectares of land worldwide—an area slightly larger than Italy. Mario Sobern of the National Autonomous University of Mexico and his colleagues investigated the most commonly used Bt toxins, which work by binding to specific receptors in pest midguts. They found three insect species that had evolved altered toxin receptors, which apparently grant Bt resistance. But the good news is that the researchers also constructed modified toxins that can kill Bt-resistant pink bollworms. These new toxins are slightly less potent than the original versions against vulnerable insects, but further research might improve them. Chew on the findings reported online November 1 by Science.