Sex Used as a Weapon Against Moths

The codling moth’s dating scene is getting a bit confusing these days.

The speckled brown and gray moths, whose larvae burrow into Washington’s lucrative apple crop, are shrugging off pesticides. So orchardists in this small town just south of the Canadian border are trying experimental techniques to turn the moths’ sex drive against them.

Growers are seeding apple trees with flexible red-plastic strips that--to male codling moths--smell like female codling moths. The strips secrete a scent that mimics the female’s distinctive chemical pheromone, making it hard for males to zero in on prospective mates.

Operators also are flooding orchards with millions of sterilized moths from a Canadian government facility in nearby Osoyoos, British Columbia. No offspring are produced when these laboratory moths mate with wild ones.

For three warm-weather months, about 300,000 sterile moths are released weekly into the 14 orchards nestled along Osoyoos Lake in north-central Washington’s Okanogan County.

“We’re messing up their sex life,” said Glenn Richardson, manager of the Oroville Areawide Project for the Agricultural Research Service, an arm of the U.S. Department of Agriculture.

The 400-acre Oroville project is one of five in the country in which the USDA is monitoring the effectiveness of mating-disruption techniques to control the codling moth population. Others are underway near Yakima and Chelan and in Medford, Ore., and Sacramento, Calif.

But the Oroville project, now in its second year, is the only one that combines the pheromone-soaked twist ties with sterile-moth releases.

“It’s really working well this year; I’m very happy with it,” said Rob Monroe, who owns five acres of apples in the project and has sprayed just twice for codling moths this year, down from the usual six or seven sprays.

The project offers orchardists a way to reduce the use of pesticides and still control the moths, whose offspring are the proverbial worm in the apple--ruining fruit so it can’t even be used for juice.

Disrupting moths’ mating habits offers additional benefits. It saves money and doesn’t pose environmental and health risks like drifting pesticide sprays. Also, reduced spraying cuts down the inadvertent killing of natural predators such as ladybugs and lacewings, which keep down aphids, leaf hoppers and other apple pests.

“No one wants to work in the chemicals,” said Craig Jones, who owns 12 acres of apples in the project and hasn’t sprayed for codling moths at all this year.

But some spraying will always be required for fruit growing, he and other growers say.

“Everyone knows that the public is demanding less pesticides. But I’m not anti-pesticide,” said Richardson at the USDA. “I was an orchardist for 15 years. I don’t believe mating-disruption can ever stand alone.”

Jones said he’ll probably continue the program even after next year, when the government will drop its $50-an-acre subsidy for use of the plastic pheromone strips.

Jack Nelson, who owns 144 acres of apples, including 120 in the project, said anything he can do to shrink his $60,000-a-year spraying budget is welcome.

“So far it’s working great,” he said. “But we’re laying our tails on the line with this. This is my life.”

As of July, orchards in the project were reporting about 0.01% damage, compared with 0.7% damage in neighboring orchards, Richardson said.

Left unchecked, the moths can be extremely destructive. Last year, an orchard not involved in the project reported damage to 17% of its fruit, he said.

Any codling moth damage harms orchardists operating on a narrow profit margin. Unlike some other apple pests, the worms always ruin fruit they infest.

Entomologists at the Washington State University Tree Fruit Research Center in Wenatchee estimate that the moths do at least $1 million in damage each year to the state’s $1-billion apple industry.