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Natural Enemies of the Emerald Ash Borer Released For First Time on National Forest

BARTON CITY, MICH., August 15, 2011 - The U.S. Forest Service, Northern Research Station and the Huron-Manistee National Forestsare working together to make Michigan’s Lower Peninsula a less hospitable place for the emerald ash borer (EAB), an invasive beetle from Asia that is causing widespread mortality of ash trees in the United States.

An initial release of tiny stingless wasps that are predators of EAB occurred in late July in Alcona County on private and National Forest lands along the eastern edge of the Huron-Manistee National Forests. While biological control has previously been implemented as a management tool for EAB in Michigan and other EAB-infested states, the release marked the first use of biological control for the insect on a national forest.

Two species of parasitoid wasps, Oobius agrili and Tetrastichus planipennisi, were approved for release on the Huron-Manistee National Forests in July. The approval was based on analysis in an earlier Environmental Assessment that concluded the wasps do not harm people, non-target species, or the environment. The Mio, Harrisville, and Tawas Ranger Districts are working with the Northern Research Station to release the wasps in a total of fourteen areas in Alcona and Iosco Counties.   

“The emerald ash borer has caused so much damage to forests and so much loss to communities in Michigan’s Lower Peninsula,” said Michael T. Rains, Director of the Northern Research Station. “Expanding the use of biological control to national forests and research on its effectiveness will contribute to more resilient forests in the future.”

These natural enemies are unlikely to save the larger ash trees. However, once the wasps become established, they may reduce the EAB population enough to curb their effect in the future, according to Leah Bauer, a research entomologist with the Northern Research Station. “I’m encouraged by the abundance of ash growing from stump sprouts, seedlings, and saplings into young, healthy ash trees in the aftermath forests of Michigan,” Bauer said. “We hope to get the parasitoids established and see if they change the outcome for future generations of ash trees.”

The two parasitoid species have different ways of preying on EAB. Oobius finds an EAB egg and injects its own egg inside, where it will hatch, grow, and kill the host egg. Tetrastichus females lay eggs inside EAB larvae, where the parasitoid larvae feed and grow, eventually killing their host.

Since it was discovered in Michigan in 2002, EAB has spread into 15 states and two Canadian provinces. This insect has killed tens of millions of Michigan’s 700 million ash trees since its arrival in solid wood packing materials from Asia during the 1990s. The EAB’s presence is noticeable on the Huron-Manistee National Forests, especially along river corridors.

The mission of the U.S. Forest Service is to sustain the health, diversity, and productivity of the nation’s forests and grasslands to meet the needs of present and future generations. The agency manages 193 million acres of public land, provides assistance to state and private landowners, and maintains the largest forestry research organization in the world. The mission of the Forest Service’s Northern Research Station is to improve people’s lives and help sustain the natural resources in the Northeast and Midwest through leading-edge science and effective information delivery.