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Scary-sounding insect released to protect Minnesota ash tree from pest

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Published  July 11, 2025 5:34pm CDT
Wild Nature
FOX 9
Scary-sounding insect released to protect Minnesota ash tree from pest

Scary-sounding insect released to protect Minnesota ash tree from pest

Minnesota's Department of Agriculture is releasing wasps in areas with known emerald ash borer infestations, hoping to slow the spread of the deadly pest.

The Brief

    • Minnesota's Department of Agriculture is releasing wasps in areas with known emerald ash borer infestations, hoping to slow the spread of the deadly pest.
    • Minnesota has about a billion ash trees and EABs could slowly kill them all without intervention. Insecticides are effective, but cost about $200 per tree, so they're cost-prohibitive, especially in woods or forests.
    • Wasps, like the 1,000 released recently in Chisago County's Ki-Chi-Saga Park, feed on EAB eggs and larva. They're tiny wasps without stingers, and they leave humans alone.

CHISAGO COUNTY, Minn. (FOX 9) - A scary-sounding insect is helping Minnesota in its battle against one of the worst pests for trees.

Emerald ash borers have already invaded millions of trees, but now it could be wasps to the rescue.

Using wasps to fight emerald ash borer

Using wasps to fight emerald ash borer

The Minnesota Department of Agriculture is using wasps in areas known to have emerald ash borer. FOX 9's Corin Hoggard has more.

Canopy Contracting

Pest invasion:

There’s not as much shade as there should be on a Ki-Chi-Saga park trail.

"These ash trees are completely, there's no leaves on them anymore because they're dying," said Chisago County Parks & Trails Supervisor Jackson McDowell.

The emerald ash borer -- or EAB -- invaded these woods and started leaving their signature squiggly pattern in the phloem of every tree they touched.

"Here's your standard D-hole, and that's where the emerald ash borer dug in and laid its eggs," said McDowell, referring to the spot where the D-shaped pest invaded an ash.

EABs have spread across at least 58 of Minnesota’s 87 counties since 2009, and American ash trees have no resistance, so in this state alone a good chunk of a billion trees are at risk, or already dying.

"Because there are no defenses that if just left unchecked, emerald ash borer probably will decimate the ash population in Minnesota," said Minnesota Department of Agriculture (MDA) entomologist Angie Ambourn.

Fighting back

Expensive options:

You can fend them off with insecticide injections, but that costs about $200 per treatment, usually every couple of years.

So it can get expensive, and it's especially cost-prohibitive in the forest or woods.

"You can't go into that kind of environment and start treating all those trees, that's not feasible," Ambourn said.

More feasible on a large scale is introducing a new predator, which is why the Department of Agriculture recently released 1,000 wasps in this park.

Wait a second. Wasps?

"The ones that we are releasing are wasps that will not sting humans, and they're so small that probably nobody's ever even going to see them," Ambourn said.

Most of them are in the pupal and larval stage in little containers in the trees.

They’ll only live if they can feed on EAB eggs and larva, so they shouldn’t create any new problems.

MDA has released them in 55 locations so far and seen some success, so these Chisago County woods at least have a fighting chance.

"Hopefully some trees will be able to survive and maybe over time they'll even develop their own defense mechanism for the emerald ash borer," said McDowell.

Buying time to get EABs to buzz off.
 

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