The Shirt on Your Back
By Andrea Peck
The cotton business is one that we seldom think about –particularly when it comes to genetic modification. But, cotton is such an important economic industry that many countries have switched gears and now grow altered cotton. Transgenic cotton or Bollguard II is genetically-modified cotton that is inoculated with genes from the oft-used pesticide, Bacillus Thuringiensis. The genes are selected to create a toxic effect in the plant to prevent insect damage. Bt, as it is commonly referred to, is considered mild, targeting only specific pests. It has been used in spray form by gardeners and farmers over the last half-century.
Though the term, “genetically modified” can send a shiver down the straightest of spines, the science and practicality behind it is worth investigating. The use of modified cotton has helped reduce the reliance on other, more toxic, pesticides. In Arizona alone, the spraying of broad spectrum insecticides, which affects beneficial insects as well as pests, has been reduced by up to 80%.
Seems like a pretty snazzy trade off. Or it would be—if it weren't for the bollworm.
Big and hulking, the bollworm destroys the bolls and squares of the cotton plant. It's difficult to conduct business when there is no product. Bt is commonly used to combat the bollworm which explains the name, Bollguard II. In the normal bollworm, a stomach protein, cadherin, binds to Bt. Death does not take long as a whole series of gut actions take place. You can only imagine what that looks like.
But, the insect world is full of fascinating things—particularly mutation. Researchers began to notice an increase in resistant bollworms. It appears that some sturdy bollworm out there in the cotton field had developed a mutation that prevented the binding of cadherin and Bt. If those two don't bind, then the Bt does not work.
India, which is the third largest producer of cotton in the world, seems to have won the lottery for genetically savvy bollworms. When looking at the cadherin gene, researchers found that the pink bollworms found in India had up to 19 mutations on that gene - far more than resistant bollworms raised in the laboratory. They found that these pink bollworms were utilizing a genetic mechanism, alternative splicing, to create massive diversity within the cadherin gene. Alternative slicing allows a single DNA sequence to create more than one variation of the protein. With all those variations, the binding effect of cadherin to Bt loses its effect.
Good news for the bollworm. Bad news for your shirt!