The super-bollworm cometh

The first bug to evolve resistance to toxins in genetically modified cotton has arrived. Should we run screaming for the hills?


Andrew Leonard
March 7, 2008 7:04PM (UTC)

Mutating bugs that resist transgenic toxins! It's the kind of news that makes Greenpeace activists shout "I told you so" and gives Monsanto scientists sleepless nights: Entomologists at the University of Arizona have documented "the first case of field-evolved resistance to a Bt toxin produced by a transgenic crop."

The insect is Helicoverpa zea, aka: the bollworm. The crop is Bt cotton, better known by the Monsanto brand name Bollgard. The Bt toxin is Cry1Ac -- death to all lepidopteran insects.

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The researchers, led by Bruce Tabashnik, chair of the UA entomology department, published their disconcerting news in the February issue of Nature Biotechnology. A good summary can be found here. But before we all go running into the streets, shrieking and rending our garments at the emergence of this long-awaited and long-feared genetically modified-induced insect mutation sure to ruin all of global agriculture, there are some mitigating circumstances to consider..

According to Tabashnik, the superbugs took longer than predicted by entomological computer modeling to arrive. The researchers evaluated large datasets of information focusing on six cotton pests in Australia, China, Spain and multiple locations within the U.S., but Cry1Ac-resistance was found only in bollworms in Arkansas and Mississippi. Newer versions of transgenic cotton include a second generation Bt toxin, Cry2Ab, for which the bollworm has as yet evolved no defense. Finally, the available evidence appears to validate the "refuge" strategy of transgenic crop pest management, in which farmers are required to plant non-Bt crops in fields adjoining Bt crops in order to provide a hospitable environment for non-resistant pests to thrive. In regions where greater acreage has been devoted to refuges, the development of Cry1Ac resistance seems to have been delayed.

The purpose of the "refuge" strategy is to prevent toxin-resistant bugs from hooking up with other toxin-resistant bugs and making lots of toxin-resistant babies. Resistant bugs are expected to be relatively rare, so if acreage is set apart for non-resistant bugs to breed that's where the bad bugs will find their mates. If the gene for resistance is recessive, which it tends to be with cotton-eating caterpillars, the hybrid babies won't express the resistant trait.

If this seems like a somewhat sloppy, hit or miss approach, well, welcome to farming. Entomologists can cite reams of computer data in support of models that recommend exactly how much acreage should be planted with non-Bt crops or what ratio of non-resistant to resistant insects is ideal for the prevention of resistance development (500-1 is considered just right). But there's no silver bullet. To provide just one example of the imponderables at work: the resistance to Cry1Ac trait in cotton pests is not always recessive. In the case of H. zea the trait appears to be statistically more dominant than in other cotton pests, which might explain why H. zea was the only one of six different lepidoptera to develop resistance, so far.

Therefore, in regions where H. zea is prevalent, entomologists might argue for a greater percentage of acreage to be set aside as a refuge, with the goal of further diluting the breeding potency of resistant bugs.

The long-term goal is not to prevent resistance from ever developing. That's not how nature works. Eventually insects will evolve resistance to any toxin, natural or human-made. The goal is to delay resistance from developing long enough so that it becomes manageable, so that, perhaps, by the time super-bollworms evolve, there are new versions of super-Bollgard available to farmers to contain the threat.

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In a perfect world in which scientists impartially evaluated data and designed rigorous management strategies which farmers and seed companies than scrupulously cooperated to execute, it's possible that the showdown between anti-GM activists and biotech companies might be a little less ideologically fraught and vituperative. But of course, farmers and seed companies operate according to financial incentives, and there are, in the short term, clear economic downsides to maintaining large refuges. Aside from providing prime habitat for precisely the bugs farmers hate most, they are also a pain in the ass to set up, they depress crop yields, and they reduce the amount of super-seeds companies can sell. Thus there is constant pressure on farming regulators to ease refuge requirements.

An excellent history of how the Environmental Protection Agency developed its refuge models, published late last year in the Southwest Farm Press, concludes with one scientist noting that the final decision on how to handle refuges was up to the EPA, "which is responsible to all those stakeholders."

But as any one who has been paying attention to the Bush administration is all too aware, some stakeholders are more equal than others. Some stakeholders end up completely coopting their regulators, and enjoy the privilege of designing their own regulations.

When the debate between anti-GM activists and Monsanto apologists becomes a shouting match in which supposedly omniscient scientists are matched up against Nature-worshipping greens, How the World Works starts to lose interest. In that kind of polarization all nuance gets lost. But when the debate is whether corporate pressure on the EPA might result in the decreasing efficacy of refuge set-asides, and thus hasten the evolution of superpowered cotton-munching caterpillars, that's where we start to get fascinated.

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Andrew Leonard

Andrew Leonard is a staff writer at Salon. On Twitter, @koxinga21.

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