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Environment & Energy

Tiny Wasps Used to Attack Ash-Destroying Beetle

The Emerald Ash Borer has destroyed or severely damaged more than 40 million ash trees in 15 states, including Pennsylvania. The beetle is native to China, but was first detected in 2002 in Michigan, and then was found in Pennsylvania four years ago. At least 12 counties in the commonwealth are infested with the pest. Past eradication efforts have not succeeded, so agriculture and forestry officials have been trying to contain the pest by placing quarantines on hardwoods.

But now they might have found a new weapon to battle the Emerald Ash Borer. Leah Bauer of the U.S. Forest Service says they went to China and found tiny, stingless wasps that are natural enemies of the Emerald Ash Borer. They brought back the wasps under quarantine and studied them for several years. Now they are releasing the wasps—which are smaller than poppy seeds—in national forests, directly onto the ash trees. "Each one will crawl through the layers of bark and in the crevices and will lay its eggs inside an Emerald Ash Borer egg and kill it," said Bauer. "It actually feeds on the inside of the (borer's) egg and a tiny little wasp will emerge from the egg." Another species of the tiny wasps lays eggs inside the beetle's larvae, where the wasp larvae feed and grow and eventually kill their host.Emerald ash borer (A) compared to two other metallic pine borers.

Eleven of the infested states have begun deploying the wasps. In Pennsylvania, the Department of Conservation and Natural Resources is overseeing this non-stinging "sting" against the beetle in forested areas.

Bauer says the wasps are harmless to humans, non-targeted species and the environment. But these natural enemies of the beetle are not likely to save the larger ash trees. "We can't eradicate the Emerald Ash Borer," said Bauer. "We're hoping to suppress the population density to a level that will allow our ash trees to at least continue producing and survive."

To do that, she says they will have to eliminate about 90% of the pests. "(The ash trees) will not be probably as useful for landscaping and other products," said Bauer. "But they'll be able to fill their niche in the environment in the forests and riparian areas."