Photo credit: Andy Raego and Chrissy McClarren

Genetically modified corn containing Bt has been used successfully in the United States for the last 18 years to fend off the migratory armyworm, a destructive pest. Now, a study published in the scientific journal PLOS One has found that populations of armyworms in North Carolina and Florida are resistant to the Cry1F protein found in Bt corn, which is typically lethal to insects. Scientists have found that armyworms from Puerto Rico developed complete resistance to Bt crops and then migrated to the continental United States. Because the armyworm moth migrates long distances (it is found all the way from Argentina to Canada), genes conferring resistance may easily be spread rapidly across a wide area. As a result, genetically modified Bt crops in both North America and South America may be at risk.