MOUNT VERNON, Ill. — That pesky, tree-killing emerald ash borer (EAB) has been discovered in two southern Illinois counties, according to the Illinois Department of Agriculture (IDOA).

It is the first time the borer has been found in counties south of Interstate 70, and it is yet another sign the pest is continuing its spread across the Midwest.

Illinois has been under a federal quarantine since November 2008, meaning no wood of any kind may be transported across state lines. At that time, evidence of the borer existed in 20 of 102 counties; with the two newest counties, that total now stands at 25, most in east-central and northern parts of the state.

The same federal quarantine limits apply to Indiana, Michigan, Ohio, Pennsylvania, West Virginia and parts of Wisconsin, Missouri and Kentucky.

“We have made strides in terms of limiting its spreading, but the fact remains that the emerald ash borer is still spreading,” said Juliann Heminghous, outreach coordinator for the IDOA.

The agency announced earlier this month the beetle was found in traps just north of Salem in Marion County and at the Green Creek Rest Area on I-57 in Effingham County.

It is estimated the small, metallic-green beetle first discovered in Michigan in 2002 has destroyed more than 25 million ash trees.

Native to Asia, the beetles’ larvae burrow into the trees’ bark, slowly starving them to death over several years.

“(The EAB) is a sneaky traveler, which is why it is important that everyone, even those counties not currently inside the quarantine zone, put the quarantine guidelines into practice by keeping all firewood and untreated wood products from movement outside of its county of origin,” stated IDOA.

There are now 25 counties within Illinois with state quarantine limits in effect; no one may transport wood across county lines. First-time penalties can be up to $500, Heminghous said.

Although more study is under way, initial results in Michigan of a new weapon to use against the EAB is showing positive signs. A certain type of parasitic wasp lays its larvae atop borer larvae in trees; as the wasp larvae develops, it eats the borer larvae for nutrition, Heminghous said.

“So far it appears to be slowing the spread of EAB in the areas of Michigan they’ve tried it,” she said.

A troublesome aspect of fighting the EAB is the delayed appearance of damage; by the time ash canopy shows symptoms of stress, the borer has been attacking the trunk for two to three years. Beetles spread to new areas primarily through the transport of firewood.

Anyone who suspects a tree has been infected is urged to contact their county extension office or state forester. More details are available at www.llinoisEAB.com