Wisconsin researchers testing ways to reduce insects' hunger for cranberries

Central Wisconsin's picturesque cranberry country has become a testing ground for a new approach to pest control: birth control for bugs.

Scientists are experimenting with a fake love potion that makes it nearly impossible for male moths to find females during early summer mating season. The research, now in its fourth season, aims to reduce insecticide use in cranberry bogs.

The technique, called mating disruption, has proved successful in field trials in reducing populations of cranberry fruitworms, the No. 1 pest for Wisconsin's $1 billion a year cranberry industry.

"We have a lot of pests that we have to deal with," said Dani Faber, a fifth-generation cranberry farmer at Cutler Cranberry Co. in west-central Wisconsin's Jackson County. "Cranberry fruitworms and blackheaded fireworms are a definite nuisance, and if they get out of hand they can ruin entire beds and entire crops."

At this time of year, cranberry growers are focused not on pests, but on harvesting this year's crimson berries. As soon as cool weather reddens the mature berries, producers flood the cranberry beds with water, and use machines to dislodge berries from the vines. Because the berries float, crews then corral them so they can be pumped or scooped out of the water for transport.

But earlier in the season, the cranberry beds are a battleground against the natural predators that devour the developing berries.

To keep the insects in check, cranberry growers have traditionally used insecticides to kill the worms when they emerge as adult moths in early June. The idea is to beat back the moth populations before they lay eggs that hatch into caterpillars and burrow in to feast on the berries or their seeds.

Steffan interferes with mating by using synthetic pheromones, which mimic the natural chemicals emitted by female moths during mating season. A California company called ISCA Technologies impregnates soft, nontoxic wax with the pheromones, and Steffan's research team spreads small dollops of them at regular intervals across a cranberry bed, at the rate of about 1,000 per acre.

The dollops look like small Hershey kisses and emit the pheromones from the biodegradable wax for a couple of months.

"In the crudest sense, it's a love letter," Steffan said. "It's a note sent by one sex of the species to the opposite sex to convey to that other individual that I am ready to mate."

When an area is overloaded with pheromones, he said, the adult males become confused and most of them can't find females to mate with.

"If they can't find mates, you don't have fertilization, and without fertilization you've effectively pre-empted the existence of the caterpillars," Steffan said. "The nice thing about it is that there's no pesticide involved."

"We had significant, substantial disruption of cranberry fruit worms mating," he said.

The researchers have also experimented with the blend of synthetic pheromones so they will also confuse the blackheaded fireworm and the sparganothis fruitworm, which emerge as moths about the same time and also damage cranberry yields.

Tom Lochner, executive director of the Wisconsin State Cranberry Growers Association, said the state produces 60 percent of the nation's cranberries, far ahead of second-place Massachusetts. Berries are also grown in New Jersey, Oregon and Washington. About 3 percent to 5 percent of the berries are packed into bags as fresh fruit, Lochner said, and the rest are processed into sauces, juices and dried cranberries.

Lochner said the biggest challenge for mating disruption is finding a practical way to distribute the pheromone-infused wax across the cranberry beds. So far, researchers have used caulking guns and battery-powered grease guns, but Steffan is using this season to study mechanized ways to apply the waxy dollops that would be more efficient, such as using unmanned aerial vehicles — or drones — or large booms similar to those that already apply chemicals and fertilizers.

"We know if we put enough out there it's going to confuse the bugs and we're going to have reductions in population," Lochner said. "But the question is how much do we have to put out there, and how do we do that, and how much does it cost?"

"Effectively it's a substitution, but the side effects are reduced residues in fruit, access to foreign markets and fewer headaches," Steffan said.

Faber said she exports some cranberries, and some countries in Europe and Asia either don't accept fruit with chemical residues, or require strict adherence to the types and amounts of pesticides that can be used. Steffan's mating disruption strategy would last longer than chemical sprays, she said, especially for the early season insects.

One of the best times to control pests is when the moths are emerging to mate in June, Faber said, which is the same time that the cranberry vines are blooming, and honeybees — some of them in colonies rented by growers — are pollinating the crop.

"A lot of pests peak around the same time that we have to depend on our native pollinators, so having some alternatives [to insecticides] would be a definite step forward in the right direction," Faber said.

Tom Meersman • 612-673-7388