Wasps Could Help Save Future Ash Trees

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Metroparks is working with a Bowling Green State University researcher and the U.S. Department of Agriculture to save young ash trees in the Swan Creek floodplain from the devastating emerald ash borer by introducing a parasitic wasp.

The emerald ash borer is an Asian beetle discovered in Detroit in 2002 and months later here in Lucas County. It has since spread to all 88 Ohio counties and across the Eastern United States and Canada, killing tens of millions of ash trees. The result has been devastating to forests in the Metroparks and across the state, where one in every 10 trees was an ash.

Rachel Kappler, Ph.D., of BGSU, who has studied the impacts of EAB on ash trees at Oak Openings and elsewhere, helped Metroparks obtain wasp parasitoids from the USDA Animal and Plant Health Inspection Service parasitoid rearing facility in Brighton, MI.

The wasps, native to Asia, are an approved biocontrol agent that use EAB larvae exclusively as hosts to feed their young.

Metroparks plans to establish a local population of parasitoids to reduce the long-term impacts of EAB on developing ash trees by allowing young trees to grow large enough to produce seeds so that local ash populations persist, said Tim Schetter, Ph.D., Metroparks director of natural resources.

The wasp won't eliminate EAB from local forests, he said, but it will help buy the native ash trees more time to adapt their own defenses to fight off the invasive beetle.

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"Although this is not a silver bullet for getting rid of EAB, parasitoids released in southern Michigan over several years killed up to 85 percent of EAB larvae at some sites," Dr. Schetter said. "We will be conducting several releases this year and next year."

While it may take the ash trees multiple generations to develop resistance, Dr. Schetter said, "We hope that eventually native ash trees will again become a major component of our healthy forests.