BT corn was created by scientists by splicing a gene into the corn that kills root worms that can destroy entire crops. The idea worked for nearly a decade but now crops in North America are suffering severe damage where BT-resistant worms have grown more common. More than half of the corn grown in North America and much of the world is BT corn. Critics of genetically modified foods say that people are now left with the worst of both worlds: GM food that has unknown effects on humans that don't work. The growing resistance of bugs to GM foods leads to the possibility of major crop losses and an uncertain future for GM foods. Al Jazeera's John Hendren reports