There's hope against an invasive Asian beetle that has been killing ash trees in North America since the turn of the century, according to a New England-based entomologist.
Juli Gould, a native of North Haven, Connecticut, has fought the emerald ash borer (EAB) and its larvae that kill ash trees by feeding on them, since the species was first identified in North America in 2002.
Five species of ash tree in the eastern U.S. were on the brink of extinction from years of attack by the beetle, according to a 2017 report from International Union for Conservation of Nature. Tens of millions of trees in the U.S. and Canada died, and the group predicted the toll may reach more than 8 billion. Across the region, the infestation has led to expensive tree removal efforts and bans on transporting ash firewood to “slow the spread”.
Gould, who retired July 1 from the Animal and Plant Health Inspection Service with the U.S. Department of Agriculture, worked on the federal project to find the right Asian wasps to kill the EAB and potentially save ash trees.
“There are insecticides that are very effective,” Gould said. “They're expensive and you can't use them in a forest economically.”
Gould said a biological control option was necessary because EAB couldn’t be located until after it had been somewhere for several years, by which time the damage had been done to the ash trees.
Putting natural predators to the test
Several species of wasp were rigorously tested at a quarantine facility on Cape Cod to make sure they only attacked the invasive beetle before they could be approved for release.
"It's not easy,” Gould said. “I mean, we're talking about taking insects that stick their ovipositor (a tube which lays eggs) through the side of a tree to attack a larva and we have to do that and replicate that in our secure quarantine facility."
Scientists first settled on three tiny stingless wasps from China: Spathius agrili, Tetrastichus planipennisi, and Oobius agrili. Then they also selected the Spathius galinae from Russia.
The wasps were first released in 2007 in Michigan, where scientists think the infestation of the invasive beetle began in the 1990s, when it arrived from Asia in wood used in shipping pallets and thrived due to a lack of natural predators in North America.
Over the years the wasps have been released in 30 states, including Connecticut, Massachusetts, Maine, Vermont and New Hampshire.
Monitoring the progress
Gould said studies are showing real evidence of success.
"We are actually starting to see recovery of ash in our biocontrol release plots. The smaller trees are getting bigger and they're staying healthy,” she said.
Scientists are still monitoring the long-term effects.
"We started looking at what was happening to the next generation of ash,” she said. “We are finding that as they got bigger, the emerald ash borer in these trees was just getting hammered by a combination of these parasitic wasps and woodpeckers.”
Gould said that while scientists are headed in the right direction, it will take decades to determine that the battle against the emerald ash borer is truly won.
This story includes reporting by The Associated Press.
