EAST LANSING — An invasive beetle that has destroyed tens of millions of ash trees in the United States and Canada may have arrived in North America a decade before it first was detected in Michigan in 2002, according to a recently released study.
Researchers from Michigan State University collected core samples from trunks of more than 1,000 ash trees in six southeastern Michigan counties.
After studying the trunks of trees killed by the emerald ash borer, they determined that it happened as early as 1997.
It took several years before the population grew large enough to kill trees, so the researchers concluded that the beetle was in the area at least since 1992 or 1993.
The insect native to Asia was detected in southeastern Michigan in 2002.
“There were probably only a few live beetles that arrived, but ash trees are common in urban landscapes as well as in forests,” said Deb McCullough, a forest entomology professor. “When they emerged, there were likely ash trees nearby, providing food for the beetles and their offspring.”
The insects tunnel under the bark, killing a tree without any sign until its foliage yellows and dies. By then, she said, several generations of beetles can emerge.
The ash borer has infested more than 20 states and two Canadian provinces. It has killed about 50 million ash trees in the Upper Midwest and threatened millions more.