Record number of gypsy moths turns fight to quarantining invasion

Gypsy moth
The gypsy moth was introduced to North America in an effort to create a silk industry. Moth populations exploded because it has no natural predators. Officials are spreading a fungus which kills the insect in hopes of slowing it's spread.
Courtesy Purdue University

Minnesota is losing its battle to keep out the gypsy moth.

For 40 years, the state has tried to keep out the pest, which strips trees of their leaves. But after trapping the insect in record numbers this year, state Department of Agriculture officials say that in far northeast Minnesota their only recourse may be to try to slow their spread.

That worries some loggers, who fear that a quarantine would hurt their business.

The gypsy moth has been in the United States since 1869, when an amateur entomologist who thought it might be an alternative to the silk worm first brought the insect to Massachusetts from France. But the bug escaped, and since then has slowly migrated west, munching millions of acres of trees along the way.

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Although the moth has made incursions into Minnesota for decades, for a long time it wasn't able to establish a strong foothold here. But that seems to be changing, said Lucy Hunt, gypsy moth unit supervisor for the Department of Agriculture.

Gypsy moth caterpillars
This photo taken in August 2010 shows gypsy moth caterpillars killed by the fungus Entomophaga maimaiga. Spores of the fungus are still alive in the bodies. Workers grind them up, mix them with soil, and apply them to the base of trees where gypsy moths are likely to land. The method is used in states to the east where the moths have infested large areas.
MPR Photo/Stephanie Hemphill

"We just completed our trapping survey last week, and preliminary numbers show that we have over 69,000 moths in the state," she said, adding that 90 percent were found in northeast Minnesota. "So we've got a significant problem up there. The numbers are the highest we've ever seen in the state."

That's more than twice as many moths as the 27,000 detected in 2009.

What's new, Hunt said, is that inspectors are not just finding adult moths, but caterpillars that feed on hardwood trees like oak, aspen and birch.

"They can eat about nine square feet of foliage apiece, so when you multiply that by thousands of caterpillars, one egg mass can hatch out 1,000 caterpillars," she said. "So you can get pretty high populations quickly."

Repeated infestations can make trees more vulnerable to other pests or drought.

The Department of Agriculture will continue to try to slow the spread of the moth by treating high risk areas of forest with a fungus that kills the bug when ingested. But Hunt said the moth population has grown to the point in Lake and Cook Counties where treatment there is no longer effective.

Earlier this year the department proposed a quarantine that would restrict the movement of logs and trees outside the two counties. Exact details are still being worked out, but timber would have to be inspected and certified, and during certain times of the year mills would have to process wood from quarantined areas within five days of receiving it.

Gary Erickson, regional manager of wood fiber and fuel procurement for Sappi Fine Paper in Cloquet, Minn., said that wouldn't be a huge headache for those handling small quantities of wood.

"But it gets to be more and more challenging as a bigger and bigger share of our supply gets to be quarantined," Erickson said. "It just gets to be more and more of a challenge to make sure you can comply with all of that."

Gypsy moth treatment
In this photo taken in March 2012, Gypsy Moth Program Supervisor Lucy Hunt sprinkles a mixture of soil and dead caterpillars around a birch tree. The caterpillars carry spores of a fungus that kills them, but doesn't harm other insects.
MPR Photo/Stephanie Hemphill

Sappi also buys wood from areas under an emerald ash borer quarantine, which has different rules.

A quarantine also would hurt loggers, argues Wayne Brandt, executive vice president of the Minnesota Timber Producers Association.

"It may be that depending on how the quarantine is done, a mill is just simply not going to want to buy their wood, or wood from that area," Brandt said. "Too much red tape. Too many processing issues."

Brandt said a better solution would be to put the entire northern half of Minnesota under a quarantine, which would make it a lot easier to move around wood within the wider area. He argues that is not worth imposing a significant cost on the industry when existing quarantines in 20 other states haven't stopped the gypsy moth's spread.

"The agencies have worked very hard, very diligently across the country to try to slow the spread," he said. "It's been wildly ineffective. The things that have been done really haven't made much difference."

While the moth's steady westward march may not have been stopped, Hunt, of the Department of Agriculture, argues that it has been slowed.

"When we first started seeing moths on the North Shore in 2006, had we not done anything, we would be to this point, quite a bit sooner," she said. "So we did buy ourselves some time."

State officials propose to start the quarantine is next spring. But Hunt said no final decision has been made yet.

She said they are eager to collect public feedback, especially now that the gypsy moth population has reached record numbers in the state.