Genesee County may hold key to stopping emerald ash borerby Elizabeth Shaw | The Flint Journal
Monday February 25, 2008, 2:20 PM
Courtesy of David Cappaert, MSU Dept. of Entomology.
An Atanycolus wasp species may be a key element in the fight against the emerald ash borer beetle. RICHFIELD TOWNSHIP, Michigan -- A handful of dying trees and rotting logs at Genesee County's parks could hold the secret to ending the emerald ash borer threat.
A study begun last year by Michigan State University researchers has turned up some exciting first-year results - including a new chemical pesticide that appears to be virtually 100 percent effective, and the discovery of a tiny wasp that may prove to be the ash borer's first true natural enemy in North America.
"We're trying to not get too excited just yet because we've got just one year's data," said MSU researcher Deborah McCullough, lead investigator on the project. "The truth is we don't know what to expect yet. But if you compare that one year's data to anything else we've done so far, it's looking pretty darn good."
How the study worked
Pesticide EB study:
- Trees at Wolverine Campground and three other sites were each given one of seven treatments, including experimental pesticide EB, applied May-June 2007.
- Tree foliage was collected several times through the summer and exposed to adult emerald ash borers. Tree bark at two sites was also tested to determine larval density.
- Trunk injection of the experimental pesticide EB was 100 percent effective.
- Continued field and lab testing proposed for 2008.
Biocontrol agent study:
- 138 log samples from 15 trees were collected from Bluegill Boat Launch and Stepping Stone Falls in December 2007.
- Studies on the logs showed a wasp (Atanycolus hicoriae) had parasitized from six to 80 percent of the emerald ash borer larvae in the samples.
- Further lab and field research on the abundance and distribution of the wasp in Genesee County parks is proposed for 2008.
The exotic pest was first found in southeast Michigan in 2002 and has since spread to become a national threat, wiping out thousands of ash trees in its path.
To date, scientists have been unable to devise an effective method for fighting the beetle and stopping its spread. Despite statewide bans on moving firewood and other control measures, the destructive beetle's presence was confirmed in at least one region of the upper peninsula in 2006.
In spring 2007, McCullough asked permission to bring her team into Wolverine Campground, For-Mar Nature Preserve & Arboretum and Genesee Recreation Area for a new study in the emerald ash borer war.
The team tried various chemical treatments on trees infested with the bug, including a new experimental pesticide simply tagged EB. The method of treatment was tested too, with some trees receiving a spray and others an injection into the trunk.
Then they collected leaves from the treated trees and fed them to adult ash borers.
The result: EB showed 100 percent mortality of adults and 99.7 percent control of larvae.
"This is not like we've found some stuff a little bit better than what we've been trying in the last five years. This is like a quantum jump," said research technician David Cappaert. "When you get something with 99 percent control, there's no question if we can repeat these results, trees will not die."
The downside: even if EB proves to be the silver bullet, pesticides are only practical for treating individual trees in a landscape setting. They can't be used in widespread application to save the millions of ash trees in forests, along waterways and in other natural areas.
That's why the study's other unexpected discovery could be even bigger: a tiny wasp that's planting its eggs in ash borer larvae within logs collected at Bluegill Boat Ramp and Stepping Stone Falls. The eggs hatch into wasp larvae which then eat the ash borer larvae.
In some of the logs the wasp destroyed up to 80 percent of the ash borer larvae in the wood.
Exact identification of the wasp is a lengthy process, but so far It appears to be a native species that until now hasn't been known to parasitize the ash borer. The wasps have also been found in samples from Seven Lakes State Park near Fenton.
"The question is: What the hell has it been doing the last 10 years when it could've been eating the ash borer larvae?" joked McCullough. "Something has changed within this particular population of this wasp - maybe a genetic change - where they suddenly recognize the ash tree and an insect in there they can develop on."
Or it might be some temporary change in the local environment causing a random, one-time event. For example, the wasp might normally seek a larval host for its eggs earlier or later in the year than when the ash borer larvae is present in late summer - but a change in temperature or humidity might have put the wasp's and ash borers biological clocks in sync.
"We need to find out where it came from and why it's suddenly being effective in this particular region, whether it's a fluke or we'll see it even more effective next year," said Cappaert. "My personal guess is it's a curiosity that won't pan out. But there is a real possibility it could contribute to the control of the ash borer here in Michigan or even nationwide."
The challenge now is to answer those questions over the coming year.
"First we write a proposal to get more funding to keep working on this," said McCullough. "That's what's on my desk right now."
Meanwhile, the Genesee County Parks Commission is more than happy to continue providing that living lab.
"We really appreciate the opportunity to participate in this study and are very excited by the results so far," said parks Director Amy McMillan. "It is so very cool to be on the frontline of the war against this pest that has been responsible for so much destruction and devastation."
