Agencies step up fight against gypsy moths

Minnesota is at the front line of a national effort to slow the spread of invasive gypsy moths, which have defoliated and killed thousands of acres of trees on the East Coast.

Although the destructive critters have slowly munched their way westward, so far they have not established a reproducing population in Minnesota, even though they have made incursions into the state for decades. But the moths are now hungrily eyeing the forests of the Arrowhead region.

State officials have been trapping and killing adult moths since 1980. But two summers ago someone found a gypsy moth caterpillar on a huge old oak tree right in the center of Duluth.

Now, Judy Gibbs proudly displays it in a small jar of rubbing alcohol on her desk in Duluth.

"It's about an inch and-a-half long, and it's very furry, with spiky little things sticking out," said Gibbs, Trees, Trails and Volunteer Coordinator for the city of Duluth.

As a "first detector," Gibbs received state training to identify the invasive pest. But she didn't need much help. She grew up in Pennsylvania, where she learned all too well what they look and sound like.

"You could hear them chewing, and you could hear their frass — their droppings — drop down out of the trees," she said. "Later on at the end of the year, when they had laid their egg masses, they were everywhere. They were on picnic tables, they were on the steps, they were under the porch. It was just gross, it was awful."

But the bugs are more than just a nuisance. They do serious damage in their caterpillar stage, stripping the leaves off one million acres of forest every year in the United States. When they were found in that Duluth oak tree, the State Department of Agriculture brought in the artillery.

Last summer, a retrofitted crop duster flew low over Duluth, dropping a bacteria over a large swath of the city to kill the caterpillars. This year the state plans to treat another 145,000 acres in St. Louis and Carlton counties, this time with a natural pheromone.

Lucy Hunt, the gypsy moth program supervisor at the Minnesota Department of Agriculture, said the scent confuses male moths by making the whole area smell like female moths.

"It interferes with their ability to find a real female," she said. "They're confused; they just fly around. Since they don't eat as adults, they run out of gas pretty quick, and within about a week or two, they die without mating, breaking the mating cycle."

Hunt attended an open house today near one of the proposed treatment areas northwest of Duluth. She said the treatments have been very effective at slowing their migration.

"Historically, the gypsy moth spread was about 18 kilometers a year," she said. "Now we've been able to get that to 7 kilometers or less nationwide on average."

Still, the moths have relentlessly moved westward since an amateur entomologist first imported them from Europe in the 1800s in a failed attempt to breed a hardier silk worm. Just last week, three counties in northwest Wisconsin were placed under a federal quarantine.

That means timber and nursery products have to be inspected before they can be transported to Minnesota, said Brian Kuhn, director of the plant industry bureau at the Wisconsin Department of Agriculture.

"The real goal here is to prevent that stuff from hitting our western counties and preventing it from getting into Minnesota any sooner than it will," he said. "Left to its own devices, this thing would be well into Minnesota."

Hunt said that while the moth prefers hardwood trees, it could do serious damage to northeast Minnesota's pine forests.

"In a pinch it will get on spruce and pine trees, and that's even more deadly," she said. "A pine tree, or a spruce tree, can't re-leaf after a defoliation, so they're really hard on those kinds of plants."

Minnesota plans to treat areas around Cloquet and north of Duluth for the moths this July. But with the main population of gypsy moths now spreading to far northwestern Wisconsin, experts concede it is only a matter of time before the infestation has expanded into Minnesota.

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