Native Species Step Up to Fight Ash Parasite

CAROLINE PORTER

When the emerald ash borer showed up in the U.S. about a decade ago, the native ecosystem didn't put up much of a fight against the Asian beetle—and the invader quickly munched its way through ash trees from Minnesota to New Hampshire, causing destruction that will cost billions of dollars to repair.

Now, however, scientists have found three reliable native allies in their fight against the scourge: Certain woodpeckers, nuthatches and parasitic wasps have developed a taste for the beetles. In conjunction with natural predators imported from the borers' original home in China and chemical treatments, the native species are helping curtail the pest after years of destruction.

The progress comes as a welcome development for what is considered to be one of the most destructive forest pests in the U.S. in recent years. Over the past 10 years or so, the emerald ash borer has infested millions of trees in 21 states, by scientists' reckoning. Various Forest Service estimates peg the potential cost at between $7 billion and at least $25 billion for state and local governments and landowners to take down or replace dead and dying ash trees over 25 years.

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But now the native parasitic wasps, red-bellied woodpeckers and white-breasted nuthatches are giving scientists new hope that they can at least slow the destruction of ash trees with the help of chemical treatments and the Chinese wasps that were imported and are now being reared in the U.S. The USDA "is working very hard to put these little enemies [the Chinese wasps] out there to become established and help control the emerald ash borer," said Ms. Bauer. Native parasitic wasps have discovered that the beetles make excellent hosts for their eggs. After the eggs hatch, the larvae snack on the ash borers.

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Red-bellied woodpeckers, which feast on the ash borers' larvae, are experiencing a population boom due to the new food supply, according to a report this month by the U.S. Forest Service and Cornell University. White-breasted nuthatches are also experiencing a population increase, according to the report. The woodpeckers also lead scientists to ash infestations, which can be otherwise difficult to spot. That is also helping the fight against the borer.

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