




"The populations are exploding," said Murphy Westwood of the Morton Arboretum in Lisle, Illinois. Infestations have been detected in 30 states.

"it's a very efficient killer," Westwood said. "As the ash borer moves through a forest, it will completely kill all of the mature ash trees within three or four years."


A sixth species, the Carolina ash, was put in the less serious category of "endangered" because it might find some refuge from the infestation in the southern part of its range, which includes Florida, Texas and Cuba, Westwood said.

Dan Herms, an entomologist at Ohio State University who studies the ash borer, called it "the most devastating insect ever to invade North American forests." It's already the most expensive because it has killed so many urban trees that had to be removed, disposed of and replaced, which has cost billions of dollars, he said.

Herms, who was not involved in the IUCN project, said he's not sure the ash species will literally disappear. But he said they could become "functionally extinct," with populations too small to play a significant role in the environment for benefits like providing shelter and filtering water.

