Expert: Ash borer beetle spread 'inevitable'

They are mean, green, ash-tree-munching machines, and experts from the Missouri Department of Conservation say the tenacious insects are not going away anytime soon.

The emerald ash borer, an invasive green beetle that attacks ash trees, continues to spread throughout Missouri. Department forest entomologist Rob Lawrence said residents and cities with a prevalence of ash trees should consider precautions.

"This is something that is ... going to spread across the whole state, so it is something we need to prepare for. It is inevitable," Lawrence said.

Ash trees make up about 3 percent of the state's tree count, according to the agency. Lawrence says in some places, that percentage is much higher.

Damage caused to a tree by an emerald ash borer pictured inside a tree. (Missouri Department of Conservation)

"In communities across the state, it averages about 14 percent of our streets' trees," he said. "But in some neighborhoods, it can be 40 to 80 percent."

Besides insecticides, the state's foresters are turning to other insects to curb the beetles' distribution.

"There is a national program to use these parasitic wasps. They come from Asia, they were tested in the laboratory for a long time to see if there were any 'nontarget' effects," he said. "They target ash trees and the emerald ash borer, they are pretty specific about that."

Essentially, the wasps attack the larvae of the emerald ash borer, which cause the most damage to trees as they mature. The wasps are nonstinging and not a threat to humans or animals.

The borers, native to Asia, began appearing in Canada and Michigan in 2002. The first infestation occurred in Missouri in 2008.

The primary cause of the insects' spread comes from people moving wood and wood products.

"Being a wood borer, (the emerald ash borer) can hitchhike on any kind of untreated wood. (It) can move by itself at a slow pace, but the way it really gets moved around is by people moving firewood or ash logs," Lawrence said.

More than 20 states in the U.S. have some kind of quarantine against the insects.