Some caterpillars are cottoning to transgenic cotton.
Genetically engineered cotton and corn produce a toxin that kills caterpillar larvae and other pests, but a new study shows that resistance to this toxin could be spreading among one species of caterpillar.
Farmers worldwide plant more than 400 million acres of these transgenic crops each year. A bacterial gene inserted into the plants' DNA enables the crops—called Bt crops—to kill insects without sprayed pesticides.
But killing vulnerable caterpillars can drive the evolution of resistance to the toxin, since only the survivors reproduce.
To keep resistance in check, farmers plant refuges of unaltered crops for the pests to eat. That way, caterpillars susceptible to the toxin may mate with the few individuals that have developed resistance. Offspring from these mixed matings are usually vulnerable to the Bt crops.