Scientists have developed another treatment for the emerald ash borer, the bug that’s killing ash trees near Northeast Minneapolis. What’s the treatment?
The borer, which is native to China, reproduces under the bark of ash trees and tunnels into the wood, eventually cutting off the flow of water and nutrients from the tree’s roots to its trunk, branches and foliage. It was first detected in the U.S. in 2002 near Detroit, Mich. The only known local infestation is near Highway 280 and Interstate 94, spreading north to about Como Avenue and south and west to the Mississippi River, with a few infested trees found across the river on West River Parkway.
The problem has economic repercussions as well as the more obvious environmental and ecological consequences. Ash trees provide wood for a multi-billion-dollar industry that produces furniture, tool handles and other wood products. The borer can wipe out acres of trees even in a relatively brief infestation.
Common treatment plans have included destroying infested trees, “girdling” infested trees with borer attractants to draw borers to already-infested trees and away from healthy ones, insecticide treatments to save individual trees, and quarantine policies to keep people from transporting potentially infested wood to uninfested areas.
The borer, however, appears to be working more quickly and effectively than these defense strategies.
Researchers noted that while the emerald ash borer thrives in China, so do ash trees, and Chinese authorities reported few instances of major tree loss due to the borer. Why do most of the ash trees survive the borer in China but not in the U.S.?
Not the kind of wasps that sting people and animals, nest in inopportune places and scare picnickers.
Researchers say these wasps are tiny and stingless, more like gnats, and are also native to China. They have not been known to harm humans or any other plants or animals. To simplify some complex entomological processes, the wasps do to the borers about what the borers do to the trees. They keep the borer population in check, disrupting the borer’s reproductive cycle (the borers do a lot of damage to the trees in their larval stage).
But when the borers made the trip from China to Detroit, the wasps didn’t come along, or didn’t survive the trip.
Researchers say they’re hoping they can disrupt the borer’s onslaught by introducing the wasps into infested areas in the United States, including parts of Southeast Minneapolis (Tower Hill Park and East River Parkway), West River Parkway and the St. Anthony Park neighborhood in St. Paul.
Depending on weather conditions, the wasps might be released as early as this week.
According to Monika Chandler, biological control coordinator for the Minnesota Department of Agriculture, three species of borer-controlling wasps have been raised in a U.S. Department of Agriculture facility in Brighton, Mich., specifically to help with emerald ash borer infestations. Two of them (tetrastichus planipennisi and spathius agrili) attack the borer in its larval stage; a third (oobius agrili) deposits its eggs inside the borer’s eggs.
“We will know how many and what gender” are released, Chandler said. “We’ll be doing multiple releases.”
The wasps that attack borers in the larval stage will be released now, and the ones that attack the eggs will be released later in the year, she said.
“We’re reuniting the target species,” she said, “and that requires a lot of testingâ€”host-specific testing.”
And these wasps, she said, are “very host-specific” and have “no significant impact” on other species.
The wasps are parasitoids, meaning that they need a host to survive in their larval stage, but become host-free when they’re adults.
“These are regulated,” she said. “It’s not something casual. These species have undergone really extensive testing.”
Researchers are hopeful that the treatment will be effective, but Chandler said there are no guarantees. “Emerald ash borer bio-
control is still very new. We don’t know how effective it will be,” she said. “We do expect that ash trees will continue to die and be removed. We just can’t make any promises.”
While the treatment has shown promise in other areas of the country, she said, it has only been tried in heavily forested areas. The Twin City area, she said, is the first urban area to test the plan. “The metro area is so urban,” she said. “We’re kind of on the cutting edge. There’s a lot of interest on the national level.”
Another potential challenge, researchers say, is the survival issue. Will the wasps survive Minnesota winters and be able to stay withâ€”and potentially controlâ€”an infestation of emerald ash borers over a number of years?
Early results are promising, they say, but not conclusive.
For Minnesota Department of Agriculture and U.S. Department of Agriculture information on the emerald ash borer and treatments for it, see the links below.