Dent Appears in Armor of Pest-Resistant Cotton

The pest in question, Helicoverpa zea, the bollworm moth
The pest in question, Helicoverpa zea, the bollworm moth USDA-Agricultural Research Service

In case we need more convincing that the Anthropocene is upon us, take a look at how we've reshaped the world with agriculture (see EcoCenter: The Land).

As Diana Parsell writes, about 35 percent of the world’s ice-free land is now under cultivation, up from a minuscule 7 percent in the year 1700. And humans are continually improving the very crops we grow, she writes: in the last 40 years, farmers have doubled their yield while planting just 12 percent more land.

Perhaps the most controversial way we improve crop yields - genetic modification - just absorbed a dose of bad news yesterday in Nature Biotechnology. Scientists from the University of Arizona reported the first case of an insect pest evolving resistance to "transgenic" cotton plants that make a pesticide called Bt. Say what you want about whether evolution is real – this change took about seven years.

Genetic engineering is a touchstone issue: it's anathema to many, while to others it's our crowded world’s only practical hope. Though GM crops are banned in the European Union, Bt-producing cotton and corn have flourished on more than 400 million acres since they were first planted in 1996, the study reports. The immense planted area created what biologists call a strong selective pressure, favoring the survival of any pests with resistance to Bt and speeding evolution of the trait.

To be fair, Bt is a model pesticide that’s been used widely since the 1950s. Far different from the likes of DDT, the chemical is produced organically, by a bacterium called Bacillus thuringiensis, and it is very specific, affecting only certain groups of insects. Most other animals can ingest it without so much as a hiccup. By genetically engineering plants to produce Bt instead of scattering it from the wings of a cropduster, farmers can avoid the collateral damage that comes from spraying plants other than their crop. And, the authors point out, resistance has so far appeared in only one of many pest species, and only in about a dozen small localities.

Still, this week's news resurrects an old hobgoblin of pesticide use. Barely a decade after the first delighted reports of DDT’s effectiveness – and the awarding of the Nobel prize to its developer – the first reports of resistance trickled in. Ever since we've seen an escalating arms race between ingenious people and adaptable insects. Already the new article’s authors are pointing to a new generation of Bt-engineered crops – these now produce two varieties of Bt to boost their effectiveness. But the writing is on the wall: resistance is inevitable.

Interestingly, a separate article in the journal reports new efforts to begin to evaluate the effect of pesticide-producing crops on “nontargetâ€? insects - the innocent bystanders and the good guys. A laudable effort, but perhaps regrettable that it’s happening 10 years after the first mass plantings. The question with genetic engineering remains: Can our knowledge of what we’re doing keep up with how fast we’re doing it?

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