The state is trying to get the jump on a growing population of gypsy moths in northern Minnesota. Researchers are engaging in early skirmishes of what will be a long war. They're choosing a few key spots to plant a fungus that's lethal to the moths, but harmless to just about everything else.
Gypsy moths were originally imported into the U.S. 150 years ago by a Massachusetts man who wanted to make silk. Ever since, they've been on a slow but inexorable westward march across the country. Right now, they're creeping into Minnesota.
Developing gypsy moths spend several weeks as caterpillars, which eat leaves voraciously enough to defoliate large areas quickly.
Gypsy moth caterpillars love oaks, but they'll feast on just about any deciduous tree. When they eat all the leaves on a stand of trees, the trees are stressed, and typically about one in five will die.
Adult male moths are grayish brown, and females are white. People have tried various weapons to fight the moths, without much success. Recently researchers discovered that a fungus, Entomophaga maimaiga, is fatal to the caterpillars.
"When the environmental conditions are right, which is a lot of rainfall, then it's a highly effective pathogen, and has done an amazing job at suppressing populations in the East Coast, all the way to Wisconsin," said Monika Chandler, who coordinates biological control programs at the Minnesota Department of Agriculture.
Chandler says the fungus eats the caterpillars, so they don't have a chance to mature to the moth stage and reproduce.
The active front in this war between moth and human is along the North Shore of Lake Superior. So last week, Monika Chandler drove to Chester Park in Duluth to deploy the latest biological weapon.
From the truck of her car, she pulls out half a dozen small plastic bags filled with potting soil, mixed with the carcasses of gypsy moth caterpillars that died from the fungus. She got them from central Wisconsin, where the battle is raging. They still contain the spores of the fungus.
"We ground them up with a blender, and we mixed them with some potting soil," Chandler explained. "We spread one bag of that potting soil at the base of each tree that we're releasing it at."
One likely tree is at the top of a steep hill. Chandler's colleague, Lucy Hunt, takes a GPS reading so they can come back to the same tree in a year or so.
Chandler scrapes some soil from the base of the tree to find out whether the fungus is already here.
"We'll take the soil sample ... we're going to chill the soil for five months in a refrigerator to simulate winter," said Chandler.
If the fungus is already in this soil, it will infect test caterpillars next spring.
"That'll help tell us whether or not the pathogen is here already, and if so where. And if we need to do additional releases, what other areas should we release in," she said.
Chandler says the fungus will eventually travel here, along with the main body of gypsy moths. But she wants to make sure it's here, ready and waiting for the growing population. It can live in the soil for six years.
Lucy Hunt shakes the ground-up caterpillars, complete with fungus spores, onto the ground around the birch tree. Next year they'll come back to check whether any caterpillars have succumbed.
Ag Department spokesman Michael Schommer says they don't expect to be able to wipe out gypsy moths completely. This pest is here to stay.
"But if we can introduce this biocontrol agent, the hope is it will help suppress the population to where it's more manageable, and you won't see as big a defoliation as you would otherwise," said Schommer.
The researchers are releasing the fungus at spots up and down the North Shore where surveillance traps have caught moths.