By George Dvorsky
Genetically modified crops are often designed to repel hungry insects. By having toxins built into the plant itself, farmers can reduce their use of environmentally unfriendly insecticide sprays. But as any first-year evolutionary biology student can tell you, insects are like the Borg in Star Trek: they quickly adapt. And this is precisely what is happening – but in ways that have startled the researchers themselves.
The discovery is a wakeup call to geneticists because it has highlighted the importance of having to closely monitor and counter pest resistance to biotech crops. The development also raises the question of the potential futility of having to change the genetic structure of crops in perpetuity; given that insects are constantly evolving, to what degree will geneticists have to go to ensure crop immunity to pests? And what does that say to the ongoing safety of such crops as far as human consumption is concerned?
Case in point are cotton bollworms. To deal with these pests, genetic scientists have developed an insect-killing cotton plant that produces toxins derived from the Bt bacterium (geneticists say that these toxins are harmless to most other creatures, including humans). But the bollworms are developing a resistance. Scientists have observed that a rare genetic mutation in bollworms makes them immune to Bt – and that the mutation isn’t so rare any more.
One scientist who predicted that these insects would adapt is Bruce Tabashnik, head of the department of entomology at the University of Arizona College of Agriculture and Life Sciences and co-author of the study making note of these findings. To stay ahead of the game, Tabashnik studied bollworms in the lab just to see how they would adapt to the toxin. Then, expecting to see the same sorts of adaptations in the real world, he took a look at bollworms in China.
What he found there was a bit disturbing. Yes, he discovered bollworms that exhibited the exact same mutations as the ones in his lab – but the Chinese insects also showed some adaptations that were completely unexpected. Speaking through a University of Arizona release, Tabashnik noted that, “[W]e also found lots of other mutations, most of them in the same gene and one in a completely different gene.”
A particularly big surprise was that the real world mutations will be more challenging to deal with from a genetic perspective. They identified two unrelated, dominant mutations in the field populations – and by dominant they mean that one copy of the genetic variant is enough to confer resistance to Bt toxin. This kind of dominant resistance cannot be readily slowed with refuges, which are specially designed plants that work to dilute the population of susceptible insects (this process makes it difficult for two resistant insects to mate and produce resistant offspring).
That said, Tabashnik acknowledged that his discovery will set the ball in motion to propel the development of new countermeasures.
As far as the real world mutated bollworms are concerned, they’re starting to take off in China. The researchers discovered that resistance-conferring mutations in cotton bollworm were three times more common in northern China than in areas of northwestern China where less Bt cotton has been grown.
In northern China, however, farmers haven’t noticed the emerging resistance yet. According to Tabashnik this is because only about 2% of the cotton bollworms there are resistant.
But he cautions: “As a grower, if you’re killing 98 percent of pests with Bt cotton, you wouldn’t notice anything. But this study tells us there is trouble on the horizon.”
This “trouble on the horizon” indicates that geneticists are in the midst of an arms race with insects. Each measure they enact will likely be countered by the ever-adapting insects. It’s difficult to know at this point just how modified the crops will have to be to withstand these pests, or how these new crops could impact on human health and the very constitution of the insects themselves.
Be sure to read the entire study.