Several invasive insects are killing trees and plants. Most of these bugs came from Asia, and are now spreading across the United States. Adelgids are attacking Hemlock trees, spotted lanternfly are going after grapes. But scientists are also using bugs to help combat the spread of some of these pests.

Grayson Highlands State Park is home to some of the state’s most rare, and unique, forest ecosystems, and it feels like an entirely different world up on the mountain. Yellow wildflowers cover the fields, and within view is Mount Rogers, Virginia’s highest peak.

This story was reported and written by WVTF

“I come here for hiking,” said Lee Diggs, pausing in her climb up a hillside. She lives in Damascus, about 30 miles away and says this is her favorite state park in Virginia.

“There’s some pretty places and they’re all different, so that’s part of what draws me here. Not just the ponies, they’re kind of cool too,” Diggs said.

Yes, she said ponies—as in wild ponies. They actually help manage the grassy bald areas of the park. Dotting the trails are reminders not to approach the ponies. There have been incidents of visitors getting too close or trying to feed them, or take selfies.

But the ponies aren’t why I’m here. I came to witness some of the state’s last remaining large ash trees

Jordan Blevins works for Virginia’s state parks, and his job is to protect native trees and plants. He says this forest has some of the last remaining healthy white ash trees he’s seen. Last year, they all looked healthy.

“But this year is the first year that I’ve seen a pretty large decline in the white ash population,” Blevins said.

Plants like goldenrod, aster and elderberry bushes dot the edge of the trail. Sixty years ago, this land was all private farmland. Today, this forest has grown up with trees. But nearly all the ash trees are sick, or have already died.

Emerald Ash Borers were first identified in the United States in 2002. “Little green, emerald colored insect that lays its eggs on the outside of ash bark,” Blevins explained. When the eggs hatch, the larvae bore through the bark and start eating the tree’s nutrients from the inside.

But a few years ago, scientists discovered several species of parasitic wasps that eat ash borers in Asia. After they made sure they wouldn’t do harm to native insects, the United States Department of Agriculture began releasing them. They worked with Blevins to release them in Grayson Highlands State Park, and throughout several other sites in Virginia. The wasps help reduce the number of trees that die.

“And the wasps don’t look like an actual wasp,” Blevins said. “They look almost like a mosquito. They’re really small. Really cool looking.”

In the last few years, scientists have released eight million parasitic wasps that eat ash borers, according to the USDA. They’re now in 30 states, and if the wasps reproduce, they could continue to protect ash trees for years. But the wasps alone won’t kill off ash borers. Likely, nothing can stop their spread at this point.

Insecticide has also kept some trees alive, and Blevins has treated some ash trees with it. On the day I visited, he held a plastic caboodle with blue liquid and other gear for injecting the trees. He said the insecticide works best as a preventative, kind of like flea medicine for your pet, but is also effective if the tree has an emerald ash borer infestation with a live canopy of at least 70 percent. Treatment costs depends on the size of tree, varying from $20 for a smaller tree and up to $100 for a very large tree. Each tree has to be treated every two years for it to work.

He drilled holes into the roots of a large ash tree, and plugged it with the insecticide.

“We’re trying to conserve, at least save a few ash,” Blevins said. “We can’t save all of them, but we’ll save as many as we can. And especially along the trail to where visitors can, maybe, sometime in the future see a big ash.”

Blevins said he’s hopeful that in 100 years, visitors to this park will be able to see a handful of large ash trees here, along with the other plants that make up a healthy forest.