Researchers are uncovering evidence for a timeline for the arrival of an invasive beetle that has destroyed tens of millions of ash trees in the U.S. and Canada.
The emerald ash borer is native to China. Scientists think it arrived in the U.S. via wood packing crates. The beetle eats through the living part of an ash tree underneath the bark and cuts off the tree's water and food supply. This starves the tree to death.
The ash borer continues to spread across the U.S. The researchers found that it may have arrived in North America a decade before it first was detected.
More from the Associated Press:
Michigan State University researchers collected cores from trunks of more than 1,000 ash trees in six southeastern Michigan counties. By studying them, they determined the year each tree was killed by the emerald ash borer and found trees killed as early as 1997.
The ash borer was detected in southeast Michigan in 2002. The researchers say it would take several years before the beetle population was large enough to kill trees, so they concluded it had been in southeast Michigan since at least 1992 or 1993.
The study is published in the journal Diversity and Distributions.
Here's how they describe their main conclusions:
Emerald ash borer was likely established in southeastern Michigan by at least the early to mid-1990s. Anthropogenic-aided stratified dispersal and the coalescence of satellite colonies with the primary population resulted in biphasic range expansion, rapidly expanding the footprint of the invasion. Our reconstruction of the emerald ash borer invasion demonstrates this invaders’ remarkable capacity for population growth and spread.