GMO-free crop “refuges” limit bugs’ ability to develop resistance

One of the most successful forms of genetically modified crops are the species that have been engineered to express bacterial proteins that are lethal to insects that ingest them. These crops have picked up the name "Bt," for Bacillus thuringiensis, the bacteria that originally made the toxins. There are Bt versions of food crops such as corn and soy beans, as well as the commercial crop cotton.

The danger with these crops is that they'll do what every other insecticide has done throughout history: select for the evolution of resistance. In the US, government regulations require that Bt crops be planted along with some fields sown with their non-Bt versions, called refuges. This ensures that any rare resistant individuals will likely mate with non-resistant animals that fed on the insecticide free crops, diluting out the resistance genes.

But China, which grows lots of Bt cotton, has no such regulations. Instead, it relies on the fact that insect pests aren't always picky about the crops they feed on. Neighboring fields of non-Bt corn, peanuts, etc. are expected to provide the equivalent of refuges. Until now, however, that idea has never been tested. But the results of tracking Bt resistance over several years are now in, and they are somewhat mixed. Refuges of other crops do work, but they've only delayed the spread of resistance.