As Emerald Ash Borer Infestation Spreads, Scientists Turn to Wasps

Jul 29, 2014

"The reality is that we're going to lose a lot of ash trees."
Kirby Stafford

The Emerald Ash Borer, an invasive insect first detected in the state in 2012, has now spread to 39 Connecticut towns. That's up from just five towns two years ago. The most recent addition? Bridgeport.

"The reality is that we're going to lose a lot of ash trees," said Kirby Stafford, chief scientist and state entomologist at the Connecticut Agricultural Experiment Station. He said the beetle, which is green and about the length of a fingernail, first appeared in Detroit in 2002, likely on wood packaging material from Asia.

From there it spread across the midwest, destroying or weakening tens of millions of ash trees. "The larvae burrow underneath the bark and then proceed to feed," Stafford said. "They create these winding galleries underneath the bark. So when a tree is hit by a sufficient number of beetles, it essentially girdles the tree," stopping nutrient flow and causing death.

Cerceris fumipennis, pictured above, is a native predator of emerald ash borer beetles. They don't sting humans or pets. Scientists are using the wasps to track the invasive bugs around the state.
Credit Wikimedia Commons

Stafford said detecting an infected tree isn't always easy. The emerald ash borer tends to attack a tree toward the top. To see up there, scientists have recruited other bugs like Cerceris fumipennis, a native wasp that preys on the invasive beetles. Stafford said cerceris picks the beetles off treetops and stores them in their nests underground. 

The state has a dedicated network of "wasp watchers" who regularly check these wasp nests for the presence of the beetles. It's called "biosurveillance," and it's how the ash borer was first detected in the state.    

One of the purple box traps used to capture emerald ash borer beetles.
Credit waitscm / Flickr Creative Commons

As for containing the beetle, Stafford said that's a lot harder. "They've tried. I mean when it first appeared there were efforts to try to eradicate the beetle and contain it. It just largely couldn't be done," he said. "A big factor is that it's so readily moved by people in infested firewood."

In response, the state put wood quarantines on four counties: Fairfield, Litchfield, Hartford, and New Haven. In addition, the state is trapping the beetles with purple box lures (found hanging in trees throughout the Northeast) and using two additional types of predator wasps introduced from Asia to reduce population numbers.