Since the late 90s, tens of millions of ash trees have died in Michigan. They were killed by the Asian Emerald Ash Borer beetle. It’s too late to save many of Michigan’s ash trees. But the Pokagon Band of Potawatomi is taking steps to insure that the next generation of trees survives.
The Pokagons are using one insect to fight another. They’re releasing parasitic wasps—the Emerald Ash Borer’s natural predator in Asia.
Vic Bogosianand his team from the Pokagon Band’s Department of Natural Resources attach a pill bottle and small piece of wood on either side of a tree. Bogosiansays the bottle has adult wasps that attack Emerald Ash Borer eggs. And inside the wood...
“There’s baby wasps and dead beetle larva in this here. And we just hang it in on the tree, and when the wasps hatch they crawl out of that and away they go,” he says.
You might think that Bogosian should be wearing some kind of protective suit, but these wasps don’t have stingers. What they do have is what’s called an ovipositor. That helps the wasps lay their eggs inside the squishy eggs and larva of the Emerald Ash Borer.
“The eggs of the wasp hatch and then the offspring of the wasp will either consume the eggs or the larva of the beetle,” says Bogosian.
Bogosian says the Pokagon band has released about 18,000 wasps so far.
Walk just about any trail in Michigan and you’ll notice that many of the ash trees are already dead. So, why bother?
Bogosiansays to the Potawatomi, these ash trees are more than just trees—they’re part of their culture. Black ash trees, for example, have been used in Native American basket weaving for centuries.
“White ash can be used to make toboggans. White and green ash can be used to make spoons and bowls," Bogosian explains. "The emphasis was originally on black ash because of the recognition that so much culture was being potentially lost.”
Bogosian is pretty confident that the wasps will work. Since the U.S. Department of Agriculture first released the wasps near Lansing in 2007, it has used this method to control Emerald Ash Borer around the country. JianDuan has been studying the wasps for the USDA.
“From 2008 or 2009 to the fall of 2014, the EAB density were reduced nearly 90 percent,” he says.
Duan says some of that is because the Emerald Ash Borer killed off so many ash trees that they essentially starved themselves to death.
Because the beetles invade areas so quickly, the wasps haven’t had much luck controlling them at the height of an outbreak. But catch them early or after an outbreak, and they’ll work.
Sounds great, right? But there might be a catch—once the wasps have killed all the beetles, won’t we have too many wasps?
Deb McCullough is an entomologist at Michigan State University. Though she’s not opposed to using the wasps, she says there could be consequences. Releases like these are often followed by textbook horror stories.
Remember the gypsy moth? The moth that’s caused millions of trees to die since it was introduced in the mid-1800s? In the early 1900s, the U.S. released its natural predator—a type of fly—to stop it. McCullough says it didn’t go very well.
“You know they released it in New England where gypsy moth was. Well this parasitoid is now way past gypsy moth, it’s out in western states that don’t have gypsy moth parasitizing native moths and butterflies. And there’s a pretty good study that came out of New England some years ago that show a big decline in the really pretty Luna moths and Cecropia moths, you know those great big ones? It coincides with the release of this parasitoid fly.”
Once the parasitic wasps are done eating Emerald Ash Borer in Michigan, McCullough says they could move on to other native insects like the Bronze Birch Borer or the Two-Lined Chestnut Borer.
McCullough says these are often seen as pests, but they’re also food for other animals. Unlike the Emerald Ash Borer, native trees have had time to build up a resistance to them.
“So it gets complicated, we don’t know a lot about the native natural enemies that attack our native insects that feed on wood and feed on the inner bark. And you don’t want to do harm, but at the same time Emerald Ash Borer is such a devastating pest that you start balancing risks and benefits,” says McCullough.
JianDuan says, right now, introducing the wasps is the only hope we have to save ash trees in the United States.
Vic Bogosiansays it will be about a year before they’ll be able to see any results. To see if the wasps are making an impact, they might try counting the adults wasps in traps, but Bogosiansays the only real way to see if it’s working is to cut down an ash tree and count the dead Emerald Ash Borer eggs and larvae.
“We’re a little hesitant to go that far because we don’t have as many ash trees left. And to cut down a healthy tree is not something we want to do. So we’re going to kind of weigh all the options. We’ll probably try a little bit of each,” he says.
Bogosian says the Pokagon Band of the Potawatomi will release more wasps next fall.
