Bt-cotton vs. the bollworm. Bollworm wins in 72 rounds!
Filed Under: Science
First documented case of pest resistance to biotech cottonNature is wicked awesome. Let me show you.
This story is about three organisms. First, we have cotton plants. Tasty, yummy cotton plants. Secondly, we have the bollworm, aka Helicoverpa zea. Finally, we have a little bacterium called Bacillus thuringiensis which produces a toxin that kills insects. We call that toxin Bt for short.
In 1996, some smart biologists decided to take the genes from B. thuringeiensis that produce those toxin proteins and insert them into the genome of the cotton plant (and potatoes and corn too). This served to make the cotton plants not so tasty to the bollworm. Tasty cotton plants become “ack-ack, plant of death!” to them. This was good because the cotton crop is worth $4.5 billion annually, and 70% of the damage caused to the crop is caused by catterpillars like the lowly bollworm.
All was well in the land of cotton for a while. But then in 2003, bollworms were found eating Bt-cotton plants! What gives? Evolution, baby!
Here are a few cool things about this. Places where bt-cotton is grown as a huge monoculture resulted in faster evolution of bt-resistance in the bollworm. Basically, the only bollworms that could be found to mate with had a tendency to be resistant, and so you got really fast resistance in the overall population. In places where bollworms could end up on non bt-resistant plants, the resistance developed much more slowly.
Now, of course the gengineers at Monsanto have upped the ante and produced a cotton variety that produces two varieties of Bt-toxin. For now, the bollworms are resistant to only one of those two. Soon, the scientists will develop another variant that kills the resistant bollworms and reset the clock.
So I looked it up, and the bollworms have a lifecycle of 30 days. BT cotton went out in 1996, and in 2003, we have levels of resistance large enough that we see it. That means in roughly 72 generations, H zea populations developed widespread resistance to the toxin.
There are two morals to this story. One: insects evolve really fast. Two: insects evolve resistance even faster when their environment is uniformly poisonous. Plant some normal plants here and there to provide refuges so that evolved resistance develops slower.
Think about the above the next time you spray everything you own with antibacterial soap.
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