What might curb the use of genetically modified crops?

The bugs themselves. Scientists have determined that five of 13 major crop pests targeted by genetic modifications to corn and cotton have evolved to where they are now resistant. The tweaks to the plants’ genes enable them to make their own insecticide. Rootworms in some U.S. states have recently developed resistance as have armyworms, maize-stem borers, pink bollworms in India and bollworms in the U.S.