DETROIT (AP) - An invasive beetle that has destroyed tens of millions of ash trees in the U.S. 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 in East Lansing collected core samples from trunks of more than 1,000 ash trees in six southeastern Michigan counties. They studied the trunks to determine the year the trees were killed by the emerald ash borer and found that to have happened as early as 1997.
It took several years before the ash borer population grew large enough to kill trees, so the researchers concluded in the study, released Tuesday, 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.
This undated file photo provided by the Minnesota Department of Natural Resources shows an adult emerald ash borer. Researchers say the invasive beetle that’s destroyed tens of millions of ash trees in the U.S. and Canada may have arrived in North America a decade before it first was detected.
"There were probably only a few live beetles that arrived, but ash trees are common in urban landscapes as well as in forests," Deb McCullough, a professor of forest entomology, said in a statement. "When they emerged, there were likely ash trees nearby, providing food for the beetles and their offspring."
Detection was made more difficult by the way the ash borer affects trees. It tunnels under the bark, destroying a tree without any sign until its foliage yellows and dies. By the time the tree shows signs of decline, McCullough said, several generations of beetles can emerge.
The infestation spread as some beetles flew from one ash tree to another, while people transporting infested ash trees from nurseries or as logs and firewood was a contributing factor.