In 2016, farmers worldwide planted more than 240 million acres (98 million hectares) of genetically modified corn, cotton and soybeans that produce insect-killing proteins from the bacterium Bacillus thuringiensis, or Bt. These Bt proteins kill some voracious caterpillar and beetle pests, but are harmless to people and considered environmentally friendly. While organic farmers have used Bt proteins in sprays successfully for more than half a century, some scientists feared that widespread use of Bt proteins in genetically engineered crops would spur rapid evolution of resistance in pests.