The Missouri Department of Conservation this month reported that the emerald ash borer has been found in 11 more counties so far this year, bringing the number of affected counties to 53.

Counties where the beetle showed up for the first time include Adair, Callaway, Cape Girardeau, Cole, Greene, Jefferson, Lewis, Lincoln, Pike, Polk and Warren. Conservation Department forest entomologist Robbie Doerhoff told St. Louis Public Radio that foresters in every county are on the lookout for the emerald ash borer.

The larvae of the metallic green beetle burrow under the bark of ash trees. The trees typically die within a few years.

The beetle is native to Asia and was first detected in Missouri 10 years ago. Humans have inadvertently aided the spread by moving firewood from place to place.

“Once the emerald ash borer is put into a new area by humans, usually accidentally, then it’s able to very quickly move on its own,” Doerhoff said. “The females will usually lay eggs on the same tree they came out of, but occasionally, females will go up to 12 miles away.”

Adults emerge from trees in April, leaving behind distinct D-shaped holes in the bark, experts said. They later mate and lay eggs on the trunk and branches. The larvae do most of the damage to ash trees, creating grooves in the wood that interfere with the flow of water and nutrients.

Conservation Department officials say the beetle kills more than 99 percent of ash trees within three to four years of initial infestation.

The emerald ash borer was first detected in St. Louis city and county in 2015. Of the 80,000 trees along public streets in the city of St. Louis, more than 15,000 are ash trees. The St. Louis Forestry Division expects a large proportion of these trees will have to be removed as the beetle spreads.

The beetle can also develop on other species, including Missouri-native white fringe trees.

Certain pesticides are often most effective on small trees with trunks less than 20 inches in diameter. The Conservation Department recommends waiting until spring to apply the pesticides.