City prepared to fight tree-killing bugs

Posted 2/27/20

When Tim Miller took over as the City of Powell’s parks superintendent, he didn’t know what to make of all the bugs in his new desk.

Rolling around in the top drawer, the insects are …

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City prepared to fight tree-killing bugs


When Tim Miller took over as the City of Powell’s parks superintendent, he didn’t know what to make of all the bugs in his new desk.

Rolling around in the top drawer, the insects are preserved in formaldehyde-filled tubes and include labels of species with names long enough to twist all feeling out of your tongue. But Miller did know one of them well: the notorious emerald ash borer.

This particular invasive species is laying waste to ash trees east to west across the country, slowly but surely making its way toward the Cowboy State.

Miller’s predecessor, former city aborist Del Barton, is a bit of a foliage fanatic and has often said of the ash borer that, “it’s not if, but when it arrives.” Barton is the one who left behind the bugs in his old desk. But in addition to leaving some specimens of the nasty ash murderers, he included some hope: In their own translucent tubes, hard to see because of their small size, are a species known to be the emerald ash borers’ arch nemesis.

The preserved dead bugs are about a third the size of a small ant, a type of non-stinging wasp in the family Eulophidae. The wasps are parasitoids: The tiny bugs lay their larvae on a host — in this case, the ash borer or its eggs. The microscopic larvae then eat the living hosts, sometimes from the inside out, until they mature.

If the wasps were much larger, they’d make a great subject for a horror film, but some researchers are hoping they could be a hero for the threatened ash trees.

American and Chinese scientists found the wasps in the forests of northern China while searching for natural predators of the invasive emerald ash borer in 2003. There are several species of non-stinging wasps, equally capable, that do little more than hunt down ash borers for food and multiply.

These wasps have no interest in humans. They won’t ruin your picnic plans or dive bomb you as you try to enter your home. Yet they’ve been reported to attack and kill up to and more than 50 percent of ash borer larvae.

Since their discovery, the U.S. Department of Agriculture has been working to study and introduce the species in an effort to control the damage to ash species across the country. A federal rearing lab in Michigan recently supplied nearly 20,000 wasps just over the border in Nebraska, according to the Lincoln Journal-Star.

The Cornhusker state is one of Wyoming’s two border states that already have emerald ash borers, with the other being Colorado; the pest was discovered in Boulder in 2013.

“The emerald ash borer is such a serious pest that they’re trying to come up with ways to manage it,” said Scott Schell, University of Wyoming associate research scientist and Extension Service entomologist. “There’s such extensive damage back East you can’t do any sort of pesticide treatments, so your only hope there is to go back to the point of origin of your pest and try to find its natural predators.”

Schell points out non-stinging wasps aren’t a “silver bullet” for urban forests. Other efforts, including collecting seeds from ash trees that are resistant to ash borers, treating trees with pesticides, closely monitoring infestations and educational efforts are important — more so than deploying biocontrol predators at this point.

“Parasitoids are most useful when you have widespread pests — where there’s no hope of eradication and you just need something to help suppress them,” he said. “In Powell, where you have a lot of ash trees, it may be more helpful to continually monitor for [ash borers] and when you locate some, you act quickly to eradicate them.”

Powell has been on guard for quite some time. Each summer, the Parks Department sets enticing traps painted purple — a particularly fetching color to emerald ash borers — in an effort to monitor the situation. They continue to plant and closely track the city’s arboretum in preparation for the day when new trees that thrive in Powell’s soil will be needed to fill the space left by those lost to the inevitable infestation, disease and old age.

Parks Department employee Jim Vanek is now in charge of the arboretum, located in Veteran’s Park, and will be tasked with many of Barton’s former duties as city arborist.

Vanek passed an exhaustive test last week to become an International Society of Arboriculture certified arborist, accredited by the American National Standards Institute. He studied for 20 months before passing the test and said the coursework was extensive.

Both he and Miller plan to stay on top of the borer threat; about 60% of Powell’s urban forest is ash.

If and when the ash borers arrive, the city and its residents will likely be spending chunks of money and resources treating ash trees with insecticides, removing the dead and planting anew. In an effort to stop losses once the emerald ash borer makes it to Powell, ash varieties were added as the most recent “outlaw tree” in the city — a designation meant to discourage homeowners from planting them.

As for the role that parasitic wasps might play, Vanek is among those who worry that introducing new species as biocontrol agents could add a new problem on top of those they were brought to control. But Schell has confidence the U.S. Department of Agriculture has gone through screening to ensure the parasitoids don’t harm good insects, like pollinators.

Schell suggests that tree owners only deploy systemic insecticides when emerald ash borers are reported near northwest Wyoming. The treatments can be costly, but “if you have an ash tree in your yard you want to protect, it may be your only option to save it,” he said.

In this area, the most probable scenario for emerald ash borers arriving will be by visitors bringing in firewood from infested areas — more than 15% of Yellowstone National Park visitors pass through Park County — or possibly through untreated pallets.

“That’s how they think [ash borers] made the big jump from back east to Boulder County, [Colorado],” said Schell.

Educating those with firewood may be our best line of defense at this point, Vanek said. The minute the Parks Department finds an emerald ash borer in a trap, there is a multi-step state response plan they’ll follow.

Until then, Miller said, “we’re not going to cut off a leg because we think we might get a sprained ankle.”