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Emerald ash borer adult.
Emerald ash borer larva.
Emerald ash borer adult (top) and larva. Images courtesy David Cappaert and

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Fungus Eyed as Stopper of Ash-Killing Beetle

By Luis Pons
April 13, 2007

Beauveria bassiana, a soilborne fungus already used for keeping many insect pests in check, is being eyed as a possible control for an invasive beetle that has already killed more than 20 million ash trees in Michigan, Ohio, Indiana, and Ontario.

Agricultural Research Service (ARS) entomologist John Vandenberg and colleagues want to know how well a commercial strain of B. bassiana stands up to the emerald ash borer after repeated applications. They are also seeing if this strain—called GHA—will work better if used with the commercial insecticide imidacloprid.

B. bassiana spores kill insects by attaching to them, germinating, and penetrating their hosts' bodies. The spores can survive to infect later pest generations. B. bassiana is used against a variety of insects, including termites and whiteflies.

The emerald ash borer is thought to have entered North America during the 1990s in solid woodpacking material from Asia. Its immature larvae feed on the vascular-system tissue of ash trees.

First spotted here in 2002 near Detroit, the destructive beetle has since cost municipalities, property owners, nursery operators and forest products industries tens of millions of dollars, according to the U.S. Forest Service (USFS). Infestations were recently found in the Chicago area.

According to Vandenberg, of the ARS Plant Protection Research Unit (PPRU), Ithaca, N.Y., preliminary studies led by USFS scientist Leah Bauer have shown that the beetle is susceptible to B. bassiana. However, the fungus' effectiveness in larger field trials has not yet been proven.

At a commercial tree nursery near Jackson, Mich., Vandenberg, Bauer, PPRU entomologist Michael Griggs, Cornell University scientist Louela Castrillo and Michigan State University researcher Houping Liu are studying the performance of the fungus on about 400 ash trees in three planting areas.

A possible strategy against the beetle would entail spraying the fungus on trees before the pests' spring mating season, according to Vandenberg.

ARS and the U.S. Forest Service are agencies within the U.S. Department of Agriculture. ARS is USDA's chief in-house scientific research agency.