By MAX COPELAND
Capital News Service
LANSING — Ash were once abundant in Michigan but now hundreds of millions of them are dead.
They were killed by the emerald ash borer, an invasive beetle native to Eastern Asia.
In a forest overlooking Lake Charlevoix, Derek Shiels says he hopes to find the trees. He’s the director of stewardship at the Little Traverse Conservancy based in Harbor Springs. He says that ash are one of the easiest trees to spot.
“Because they’re all dead,” Shiels said, laughing.
The conservancy works in Cheboygan, Mackinac, Emmet, Cheboygan, Chippewa and Charlevoix counties.
Shiels starts walking on a trail and almost immediately finds what he’s looking for.
“Here’s one of the standing dead ash trees right here in front of us,” said Shiels. “As we come over the ridge here, you can start to see—just a scattered—almost a graveyard of ash trees.”
This is the story of ash that many Michigan residents are familiar with. The emerald ash borer is a tiny, metallic-green beetle. Its larvae bore into the inner bark and stop the flow of nutrients.
It invaded Michigan in 2002. Within a matter of years, it spread throughout the rest of the country from the Atlantic to the Rockies, killing so many trees so quickly that it looked like ash would be eradicated.
“There’s a dead tree every 10 to 15 feet here,” said Shiels
But there is another part to this story. In 2007 a branch of the U.S. Department of Agriculture introduced tiny parasitic wasps in Michigan. They specialize in attacking the ash borer.
The first one is called Tetrastichus planipennisi. The female lays a clutch of eggs inside emerald ash borer larvae. The wasp larvae hatch and eat their way out.
The population of Tetrastichus picked up and started playing a significant role about five years after their release in Michigan. They spread quickly and are now killing emerald ash borer all over the state and country.
Jian Duan is a research entomologist who spent the past 12 years studying emerald ash borer for the Agriculture Department. He says those wasps are responsible for cutting the ash borer’s growth rate by about 40%.
There are five species of parasitic wasps in Michigan, including a native one. Oobius agrili is another introduced wasp impacting the beetle in Michigan.
This wasp lays its eggs inside the eggs of the emerald ash borer.
Within a week, the infested eggs change from looking like plump golden raisins to shriveled black currants, and die. These wasps kill the invasive beetle before it damages the tree. Just like the other wasp, this one is highly selective in what it feeds on.
“What is really neat is that this tiny wasp—we still have not figured out how—they only go to fertilized eggs,” said Duan. “They will not waste their eggs on unfertilized eggs.”
The Oobius agrili has another cool trait, too. It can reproduce asexually.
“These wasps do not need males,” said Duan. “That’s the beauty. They’re only females. So, the mother produce daughter.”
Which may expedite propagation.
“In the forest, you know, it’s hard to find a mate,” said Duan.
Parasitic wasps are established in 22 states, killing ash borers across the country. Which is good for the ash.
“Ash are going to survive in Michigan,” said Duan. “We even saw healthy reproductive trees.”
Back in Charlevoix, Derek Shiels of the Little Traverse Conservancy is generally skeptical that any ash will live to old age, but he did find some saplings.
“Yup, here’s a young ash,” said Shiels pointing to a chest-high tree.
“Because we see this little ash sapling here there’s hope,” said Shiels. “But it’s going to be several decades before they reach into the overstory and big tree status.”
For now, the future of big trees lies with these tiny wasps.
Max Copeland reports for Interlochen Public Radio in partnership with the Knight Center for Environmental Journalism.