Invasive Asian bug threatening Michigan's hemlock trees

It's an odd bug from Asia that doesn't need males to reproduce and spends almost all of its life in one spot, eating and eating, as it encloses itself in a waxy, wool-like cocoon for protection.

And it poses a major threat to Michigan's 170 million hemlock trees, with implications far beyond forest health — also threatening the health of rivers and streams and ultimately the state's recreational fishing industry.

The hemlock woolly adelgid has been a problem in the eastern U.S. for decades, but the invasive species had been held largely in check in Michigan. Now, that seems to be turning for the worse.

On June 21, the Michigan Department of Agriculture and Rural Development announced a quarantine prohibiting the movement of hemlock trees out of four west Michigan counties — Allegan, Muskegon, Oceana and Ottawa — after larger-scale hemlock woolly adelgid infestations were discovered in hemlock tree stands.

Seeing the devastation happening in eastern states, the Michigan Department of Agriculture and Rural Development installed a pre-emptive import quarantine on hemlock trees coming in from affected states in 2002. But the adelgid still made its way here, first detected in Harbor Springs in Emmet County in 2006 and popping up in other counties ever since.

Previous infestations were limited to individual trees or small groups and were turned back through the use of pesticides, said Mike Bryan, a plant industry specialist with the state agriculture department.

"These recent detections are more widespread," he said. "Once you get beyond a single property, it becomes difficult to control."

The tiny, aphid-like adelgid — oval-shaped, dark gray females are only about 1 millimeter long — is native to Japan, and was inadvertently transported to the U.S. in the 1950s. It's hard-wired to want to feed on hemlock trees, turning down even other evergreen species.

© 2017 Detroit Free Press


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