The emerald ash borer, which has destroyed tens of millions of ash trees in the U.S. and Canada, may have arrived in North America a decade before it was ever detected.
Researchers from Michigan State University collected cores from the trunks of more than 1,000 ash trees. During the study, they were able to see what year each tree was killed by the beetle.
The earliest trees were killed in 1997, according to the study.
Previously the ash borer had not been detected in Michigan until 2002. Because it would take several years before the borer population was large enough to kill trees, researchers now believe it has been in Michigan since 1992.
Recently, about 400 dead ash trees has to be removed from Aloha State Park near Cheboygan because of the invasive beetle.