From the University of Arizona UA News:
Photo: A pink bollworm caterpillar emerges after devouring the seeds within a cotton boll. This devastating pest quickly evolved resistance to genetically modified cotton in India, but not in the Southwestern United States where a coordinated resistance management program has been in place since the biotech crop was introduced in 1996. (Photo: Alex Yelich/The University of Arizona)
Since 1996, farmers worldwide have planted more than 1 billion acres (400 million hectares) of genetically modified corn and cotton that produce insecticidal proteins from the bacterium Bacillus thuringiensis, or Bt for short.
Bt proteins, used for decades in sprays by organic farmers, kill some devastating pests but are considered environmentally friendly and harmless to people. However, some scientists feared that widespread use of these proteins in genetically modified crops would spur rapid evolution of resistance in pests.
A team of experts at the University of Arizona has taken stock to address this concern and to figure out why pests became resistant quickly in some cases, but not others.
Bruce Tabashnik and Yves Carrière in the department of entomology at the College of Agriculture and Life Sciences, together with visiting scholar Thierry Brévault from the Center for Agricultural Research for Development, or CIRAD, in France, scrutinized the available field and laboratory data to test predictions about resistance. Their results are published in the journal Nature Biotechnology.
"When Bt crops were first introduced, the main question was how quickly would pests adapt and evolve resistance," said Tabashnik, head of the UA department of entomology who led the study. "And no one really knew; we were just guessing."
"Now, with 1 billion acres of these crops planted over the past 16 years, and with the data accumulated over that period, we have a better scientific understanding of how fast the insects evolve resistance and why."
Analyzing data from 77 studies of 13 pest species in eight countries on five continents, the researchers found well-documented cases of field-evolved resistance to Bt crops in five major pests as of 2010, compared with only one such case in 2005. Three of the five cases are in the United States, where farmers have planted about half of the world's Bt crop acreage.
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