Ash tree pests spreading in Wisconsin MILWAUKEE, June 22 (UPI) -- An invasive pest that has killed millions of ash trees in the eastern United States and Canada has been found in yet another Wisconsin county, officials said. Emerald ash borers, which have been found in 11 Wisconsin counties since 2008, were detected in Waukesha Country for the first time, state agriculture officials said Thursday. Private arborist Dave Farina examined a suspect tree near the village of Mukwanoago. "I looked at it and I saw right away that it was emerald ash borer," Farina told the Milwaukee Journal Sentinel. Farina notified the Department of Agriculture, Trade and Consumer Protection, which confirmed the pests' presence. In addition to Waukesha, emerald ash borers have been found in, Ozaukee, Washington, Walworth, Brown, Crawford, Kenosha, La Crosse, Milwaukee, Racine and Vernon counties, the Journal Sentinel reported. Emerald ash borers, metallic green bugs native to Asia with no natural enemies in the United States, were first discovered in this country in the Detroit area in 2002. The pests kill ash trees when larvae burrow into a tree and interrupt the flow of nutrients.