Replacing Pesticides With Genetics

Every spring, a host of unwelcome visitors descends on the Hansen farm in upstate New York. Diamondback moths blown in from the South threaten rows of cabbages to be sold for slaw and sauerkraut.

The moths can’t be fought off with a single insecticide. Workers must spray a series of chemicals throughout the growing season to keep the moths’ numbers in check.

“You have to rotate what chemical you use so you don’t get a buildup in resistance,” said Ed Hansen Jr., whose family has farmed the land for nearly a century. This adaptability, he said, makes the moths one of the worst pests to deal with each season.

At a university laboratory down the road, scientists are hoping to substitute sex for sprays. They have genetically modified thousands of diamondback moths, infusing them with DNA designed to kill female larvae. In August, the researchers began introducing the altered moths into outdoor cages in a field, where their mating habits will be monitored.

If the results are promising, the transgenic moths will be released into a small cabbage patch next summer. It would be the first experimental release on American soil of insects genetically engineered to self-destruct.

A plan to let similar transgenic mosquitoes loose in Key West, Fla., has met with strong opposition amid fears about being bitten. But federal regulators seem to have few worries about the safety of the moth experiments.

“Our goal as a community is to reduce the amount of pesticides used in agriculture,” said Anthony Shelton, the entomologist running the experiments at the Cornell University Agricultural Experiment Station. “Why not use genetics to accomplish this?”

An invasive species, the diamondback moth was once a minor nuisance. It became an agricultural headache in the late 1940s as chemical pesticide use exploded. The moth, the first crop pest to evolve resistance to DDT, multiplied as feebler competitors died off.

Today, the pest is found where kale, broccoli, Chinese cabbage and other cabbage cousins grow. Hungry caterpillars that hatch from eggs laid on the plants cost farmers an estimated $5 billion a year worldwide. And the diamondback moth continues to adapt to new generations of pesticides. In Malaysia, it is immune to all synthetic sprays.

In the 1990s, scientists searching for alternatives to pesticides bombarded diamondback moths with gamma rays to sterilize them. This tactic had eradicated from the United States a parasitic fly larva called the screwworm; for decades, hordes of radiation-sterilized male flies were released in the wild, outcompeting fertile males and reducing the population.

But the diamondback resisted even radiation. So Oxitec, the British biotechnology company working with Dr. Shelton, found another way to sabotage diamondback reproduction. The company, an Oxford University spinoff, stitched together scraps of DNA from a virus and a bacterium to make a gene deadly to female insects.

A female larva harboring the gene is dependent on regular feedings of the antibiotic tetracycline to survive. Out in the wild, she dies long before reaching adulthood.

Read more: Replacing Pesticides With Genetics

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