Sunday, February 5th, 2023
Sunday, February 5th, 2023

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Mankato parks on the front lines of hunting invasive insects

Asian longhorned beetles are doing damage to trees elsewhere, including in the United States, but haven't been found yet in Minnesota.

MANKATO, Minn. — The bags of bugs are piling up in the walk-in freezer in St. Paul, about 150 arriving every two weeks, a number expected to rise to well over 1,000 by the end of September.

If the sack of insects from the trap at the top of Sibley Park’s hill is any indication, Angie Ambourn will have picked through through more than 30,000 bugs by the time she pulls the final bag from the freezer sometime next winter, the Mankato Free Press reported.

With each bag, Ambourn will be searching for specific species she hopes she never sees. Zero for 30,000 would be a perfect score.

Supplying half of the dead bugs will be Patrick Walrath, who drives from Winona to Mankato to St. Cloud to Forrest Lake checking the 74 traps he’s laid, including a pair at Sibley Park and couple more at Rasmussen Woods Nature Area. He places them in trees on public land, baits them with chemicals that attract different types of insects and checks them every two weeks.

Walrath fights off mosquitoes, ticks and poison ivy to do his best to capture quarry that, he hopes, doesn’t exist in Minnesota.

So far, so good.

Since the traps went out in April – Walrath’s 74 in the southern part of the state, an equal number tended by a counterpart in the northern forests – they haven’t captured a single Asian longhorned beetle, not a solitary velvet longhorned beetle, nary a hint of any of the 17 invasive species that are the focus of the hunt.

“None,” Ambourn said during a visit to Mankato Thursday.

“That’s a good thing,” Walrath said. “It’s a job where you want to do your job and not find anything.”

Nearly 30 cities are home to traps statewide, said Mark Abrahamson, assistant director of the Plant Protection Division of the Minnesota Department of Agriculture. Most are in larger cities, because most of the invasive species are arriving via commerce – typically wood products from Asia.

Funded for one year by a U.S. Department of Agriculture grant, work began in April, all the traps were out by early May and the survey will be completed by the end of September.

“The best case is there’s nothing here and we don’t find it,” Abrahamson said.

The worst case is there’s something here and they don’t find it. In that scenario, years could go by as a tree-killing, orchard-devastating, vineyard-wrecking new pest arrives, reproduces, spreads and establishes itself before any counterattack is launched. Most of the species – such as the Asian longhorned beetle – are doing damage elsewhere, including in the United States, but haven’t been found yet in Minnesota.

“We have a better chance of taking action against them if we find them early,” Walrath said. “That’s kind of the goal of the survey.”

The stakes in fighting invasive species are high, for property owners with cherished trees, for workers and industries that rely on forests, for farmers of everything from grapes to soybeans. Walrath, who has also collected bugs for pest surveys involving row crops like soybeans and potatoes, said it all goes back to protecting the state’s resources.

“I like to think that the woods, the water, the agriculture are what’s important,” he said. “And if I can do anything to help that, I’m in.”

Walrath said the lures he uses, which mimic insect pheromones or smells emitted by unhealthy trees, have scents so strong his brain has scent-flashbacks on his off-days. He talks of removing multiple ticks at the end of a long day. And he knows what lure is particularly attractive for species such as aedes vexans: himself.

“This week, a million,” Walrath said when asked how many mosquitoes he’s seen while checking the traps. “The last two weeks have been ridiculous. I think they’re over the whole concept of DEET. I don’t think they care any more.”

Dealing with the traps isn’t a quick process, either. The contraptions have to be lowered from the trees, lures have to be replenished, the liquid goop at the bottom of a trap has to be run through a coffee filter to screen out the insects … . And when he gets through all 74 traps, two weeks have elapsed.

“It’s like painting the Gold Gate Bridge,” he said. “When you get done, start over.”

As for Ambourn, a bag of insects isn’t always a bouquet of roses.

“Sometimes they get a little icky,” she said, particularly during hot, wet weather – especially if the carrion beetles find the trap and start feasting.

But a good clean batch like the one from Sibley Park …

“This one’s a longhorned beetle. It’s a native. That’s a redheaded ash borer,” Ambourn said, using a tweezers to pick another native Minnesotan out of the glob of insects and tree bits at the bottom of the filter. “That looks like a click beetle.”

“I think Angie’s in her element,” Walrath said.

“There’s some interesting stuff in here,” Ambourn said. “I mean, if you’re an entomologist.”

Some of the targeted species are large and distinctive, others require a microscope to count spines or leg segments or antenna segments. Any that Ambourn is uncertain about or that she believes are of interest are shipped to university laboratories around the country that specialize in particular insect types.

While it takes someone like Ambourn to tell the difference between a velvet longhorned beetle and a banded elm bark beetle, she and Walrath said it’s imperative that average Minnesotans also pitch in when combating invasive species.

First and foremost, people should burn local firewood when camping or going to the cabin – not haul it from one part of the state to another. Second, they should take an interest in insects that seem to be attacking a tree or other plant, take a picture or notes and report it to

And shoppers should consider invasive species when buying furniture, especially log furniture. Ask where it comes from and consider buying an alternative produced in Minnesota. As for folks who already have furniture from Asia, if they see a bug emerging from a burrow in the wood, catch it.

“Arrest the pest,” Walrath said.

“If you think it’s something you’ve never seen before, call it in,” Ambourn said. “Better safe than sorry.”

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