A ninth Minnesota county was named Thursday as having an infestation of emerald ash borer, the invasive pest that already has killed tens of millions of ash trees in 25 states.

Two adult emerald ash borers were found in Chisago County on a survey trap, and tunneling was discovered in a nearby tree, the Minnesota Department of Agriculture (MDA) said.

The bugs were found near Manning Trail not far from Chisago City, just north of the border with Washington County.

That means Chisago County likely will be placed under emergency quarantine in the coming week and eventually join Anoka, Dakota, Fillmore, Hennepin, Houston, Olmsted, Ramsey and Winona counties in a state and federal quarantine, the MDA said.

Emerald ash borer larvae kill trees by tunneling into the wood and feeding on the tree’s nutrients. The invasive insect was discovered in Minnesota in 2009.

The last county where the pest was found, Fillmore, was quarantined in April. The quarantined counties in Minnesota are either in the metro area or the southeastern part of the state.

Minnesota is highly susceptible to emerald ash borer destruction because of its 1 billion ash trees, the most of any state in the nation.

Quarantines help prevent emerald ash borer from spreading outside of a known infested area, the MDA said. A quarantine is designed to limit the movement of anything infested with the bug, including ash trees and ash tree limbs as well as all hardwood firewood.

Specimens from Chisago County have been sent to USDA for confirmation, which is expected early next week.

To control the pest, the MDA recommends the following:

• Don’t transport firewood; instead, buy it locally from approved vendors and burn it where it’s purchased.

• Be aware of quarantine restrictions on movement of products such as ash trees and wood chips.

• Watch ash trees for infestation.

For details, go tomda.state.mn.us/eab and use the “Does My Tree Have Emerald Ash Borer?” guide.