GENEVA, N.Y. — 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.
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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.
In a study published in BMC Biology in July, male moths carrying the gene wiped out communities of normal moths living in small cages. Females mating with transgenic males had as many offspring as those coupling with unaltered males, but the female offspring died before being able to reproduce.
Only some of the male offspring inherited the synthetic gene, which tends to disappear after a few generations. So thinning the moth population required multiple waves of assault by fresh males bred in the lab.
Dr. Shelton’s outdoor cages, also stocked with wild moths, will test how well the genetically engineered males compete in a bigger arena. The release next summer into the field would take the technology one step closer to being used on farms.
The strategy has drawn criticism. Groups opposed to the use of genetically modified organisms worry that the protein made by the synthetic gene could harm wildlife that eat the moths.
“We would argue that more information should be collected,” said Helen Wallace, the director of GeneWatch U.K.
Haydn Parry, the chief executive of Oxitec, says the company addressed this concern and others in data submitted to the Department of Agriculture.
“We fed the protein to mosquitoes, fish, beetles, spiders and parasitoids,” he said. “It’s nontoxic.”
After weighing the evidence, the department decided the planned experiments would have no significant effect on the environment.
A public letter signed in June by the Northeast Organic Farming Association of New York protested any outdoor trials. The association cautioned that escaping moths could contaminate nearby farms and endanger their organic certification.
Yet studies suggest the likelihood of diamondback moths straying is low. Wild moths released into the open tend to stay put as long as they have food and company. Any that do venture farther afield are likely to be wiped out by New York’s cold winter.
Even if strays are found, legal experts say that national organic standards penalize only the deliberate use of a genetically modified organism.
“If these moths came across into an organic field inadvertently, that would not be a problem for the farmer,” said Susan Schneider, a professor who specializes in agriculture and food law at the University of Arkansas School of Law.
Insects that do wander into other fields can be identified by their red glow under ultraviolet light — caused by another gene inserted into their DNA, this one from coral.
Even if the moths in Dr. Shelton’s experiments pass muster, there is still no guarantee that farmers will use them.
“At the end of the day, the technology may not go forward for commercial reasons,” said Mark Benedict, an entomologist at the Centers for Disease Control and Prevention.
Other weapons developed for combating diamondbacks — larva-eating wasps, for instance — have struggled to compete with cheap chemical pesticides.
“What almost always happens is the pesticides take precedent,” said Michael Furlong, an entomologist at the University of Queensland. “The growers can’t resist spraying, as it’s the easiest thing to do.”
As for Mr. Hansen, he says he has not ruled out using the genetically engineered moths one day in the continuing battle to save his cabbages.
“I’m glad they’re doing these experiments,” he said. “But it’s really early days.”
By DEVIN POWELL of The New York Times
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