Long Term Hope for Control of the Emerald Ash Borer

Long Term Hope for Control of the Emerald Ash Borer

“It is a kind of all-American tree, growing everywhere east of the Rocky Mountains. It is used by most Americans, for sports equipment – baseball bats, tennis racket frames, hockey sticks, bowling alley floors, oars, polo mallets – as well as for tool handles and porch furniture. And to top all of this, it is a beautiful tree,” wrote Hal Borland in “A Country Man’s Woods,” published in 1983.

The Last Green Valley is 84 percent undeveloped land, the vast majority of which is in forest, and it’s this deep wooded landscape that makes our region a wonderful place to live and a large reason why it was designated a National Heritage Corridor. The trees in our woods are predominately deciduous with species of oak, hickory, birch, maple and ash being the most familiar and easy to identify. But it’s the beautiful and useful ash facing a particularly sad fate.

The quote from Borland highlights what many of us don’t realize about ash trees. For centuries they have been important to the daily lives of humans with their many utilitarian uses. Ash wood is hard and flexible, easily worked and shaped. This is true not just for sports equipment and tool handles, but also for electric guitar bodies. It was the favored wood by Indigenous tribes of the northeast for making baskets, especially the black and brown species of ash. Its history is deeply ingrained in our lives, making the deadly impact of the invasive insect the emerald ash borer (EAB) even more tragic.

Forests in the eastern United States are about 7 percent ash trees, and here in The Last Green Valley they comprise about 5 percent of our deciduous species. Unfortunately, the Connecticut Agriculture Experiment Station estimates all the mature ash trees will be dead in the next decade in Connecticut and beyond due to the massive infestation of EAB.

It was 10 years ago, during the summer of 2012, that the emerald ash borer was first discovered in both Connecticut and Massachusetts. It was unknown in the U.S. before being discovered in Michigan in late 1990s, probably arriving from its native regions in Asia in packing crates and wooden pallets in shipping containers. By 2010 it had spread into 14 more states, including the entire mid-west and mid-Atlantic states, eventually reaching New England in 2012. As of June, EAB has been found in 36 states and the Canadian provinces of Ontario, Quebec, New Brunswick, Nova Scotia and Manitoba.

The emerald ash borer is a small, metallic green beetle about a half inch in length that feeds almost exclusively on ash trees. During its life cycle it undergoes a complete metamorphosis, starting as an egg laid on the bark of the tree. The egg hatches in 7 to 10 days into a larva (grub) which burrows in the bark to feed on the phloem and cambium layers of the inner bark.  The EAB becomes a pupa and then an adult beetle emerging from inside the ash tree to feed on its leaves before the cycle begins again.

The phloem and cambium layers the larva has fed on are the critical growth and circulatory system of the plant, transporting sugars produced by the leaves and responsible for life and health of the tree. The EAB cuts off the flow of this food and its tunnels in essence girdle the tree. Successive years of EAB infestation will kill the tree within 2 to 3 years and entire stands of ash trees within 10 years.

Despite the ominous fate of our mature ash trees there is hope for their future thanks to tiny parasitic wasps. I learned about the introduction of these wasps into Connecticut from Dr. Claire Rutledge, Associate Agriculture Scientist at the Connecticut Agriculture Experiment Station, where she is responsible for monitoring and biological control of wood boring insects. Rutledge has been leading this effort in the state, and I attended a webinar organized by the Yale Forestry Forum where she spoke about the biological control of EAB in Connecticut. Here are some of the key points from her presentation.

Our native ash trees have little resistance to the emerald ash borer and the insect has no natural predators in our region. As a result, it spreads quickly, in part due its flying ability, and is accidently transported from region to region by people moving wood.

The biological control being used to battle EABs entails parasitic wasps that are its natural predator. The parasitic wasps used to control EABs evolved in the same part of the world, and in their native range in Asia effectively control the borer from decimating the species of ash growing there.

Research and trials on the effectiveness of the parasitic wasps was a five-year process, and critical to ensuring that the species of wasps and EABs are “tightly linked.” It was important to confirm the wasps are not likely to switch to a secondary prey and attack other native beetles. The wasps lay their eggs inside the body of the EAB, eating their way out as they grow and pupate.  There are three types of parasitic wasp used to control EAB, each designed to attack them at different stages in the beetle’s life cycle.

The wasps were brought to the U.S. from Asia, bred by the swarm in the Midwest (a region that has been battling EAB for longer that we have) and shipped to Connecticut for release. They have been in use since 2013 and so far, the results have been promising for the future of our native ash trees. Unfortunately, it is too late for our mature ash trees that are too far gone for the parasitoids to be effective.

According to Dr. Rutledge the effective return of our ash species won’t begin until the emerald ash borer infestation has run its course and the population collapses. Unfortunately, that requires the EAB food source, ash trees, to be gone. With the help of the parasitic wasps keeping the EAB population in check, ash trees can resprout from stumps and have a better chance of survival.

We have several mature ash trees in our neighborhood in Putnam, and already I am seeing the early signs of EAB infestation. I know in the next few years we’ll be cutting down the ash trees on our property, but I also know the stumps will resprout and, hopefully, reach maturity, free of threat from the emerald ash borer.

To learn more about the emerald ash borer infestation and efforts to control its spread, I suggest watching the recording of the webinar with Dr. Rutledge:


Information can also be found at the CT DEEP website: https://portal.ct.gov/DEEP/Forestry/Forest-Protection/Emerald-Ash-Borer-EAB

Information is also available at the Connecticut Agriculture Experiment Station website:


Bill Reid is the Chief Ranger of The Last Green Valley National Heritage Corridor. He can be reached at bill@tlgv.org or by calling 860-774-3300.

Exploring The Last Green Valley, Sunday, December 11, 2022

The Norwich Bulletin is granted first serial rights and associated electronic rights to publish the following article. The Last Green Valley, Inc. retains all other rights to the work.


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