In our woods at Mary Virginia Crites Hannan Park, along our streets and roads, in our state parks and national forests, and in our own backyards, a battle is raging. It began in the early 1990s.
An invader, a shiny green beetle, only about a half-inch long, first broached our shores in Canton Township outside Detroit. Concealed in solid wood packing crates in its larval stage, it soon emerged as an adult and began an invasion that went undetected for 10 years. This tiny insect was the Emerald Ash Borer (Agrilus planipennis), a non-native, invasive beetle originally from northeastern Asia, an area including Russia, northern China, and Korea.
Although damage to and death of ash trees was investigated much earlier, it was not until 2002 that the Emerald Ash Borer (EAB) was identified as the culprit. Even then, little was known about the insect. In its native range, it caused minimal problems. The ash trees there had long ago developed natural defenses against it. So, because it was not seen as a threat to ash trees in Asia, no research had been done. Once researchers in North America recognized the danger, they had to begin their investigations almost from scratch.
In the meantime, EAB was mounting a full-fledged war against all ash trees native to North America. It was spreading fast and efforts to contain it were ineffective. Now, 17 years after the initial discovery, EAB has been found in 35 states from as far north as Maine, south to Georgia, as far west as Texas and Colorado. It has penetrated the forests in five Canadian provinces. Experts estimate that EAB has so far killed 100 million ash trees.
The EAB’s attack on an ash tree begins when it flies to a likely tree and feeds on the leaves, causing little damage. The damage comes during the larval stage. After mating, the female lays her eggs in crevices in the bark. Once hatched, the larvae chew through the bark into the inner phloem. This is the vascular system of the tree, carrying water up into the branches and leaves and bringing sugars and other nutrients down into the roots. The EAB tunnels through this layer, feeding, growing larger, and cutting off the tree’s circulation. The larvae pupates and then emerges from the tree as an adult, leaving a small but distinctive “D” shaped hole in the bark. The tree will begin to show signs of infestation such as canopy dieback, sprouts growing from the trunk, bark splitting and increased woodpecker activity within one to two years. By this time the tree is already half dead.
Researchers at the U.S. Department of Agriculture, as well as numerous state agencies, were desperate to mount a counterattack against EAB. A number of methods were tried to curb its spread including quarantines of infested areas, eradication, clearcutting an area to create a barrier that the borer wouldn’t cross. Each of these methods was ruled out.
Researchers finally settled on biological control as a last hope to contain EAB. Biological control, also known as biocontrol, is the practice of importing, and releasing for establishment, natural enemies to control an introduced (exotic) pest. First, researchers had to identify EAB’s natural enemies. They found that, in its natural habitat, EAB is preyed upon by a number of tiny, parasitoid wasps. A parasitoid wasp lays its eggs on the eggs or in the bodies of other insect larvae. When hatched, the wasp larvae feed on the egg or larvae of the host, eventually causing its death. Between 2007 and 2012, three different species of stingless wasps from northern China were chosen for experimental release into test areas in Michigan, New York and Connecticut. Results were mixed.
In 2016, a fourth species, Spathias galinae, from Russia was released in areas of New York, Connecticut and Massachusetts. Results with this species have been more encouraging but questions about its cold tolerance and ability to spread through a range are still to be answered. Researchers remain hopeful that, despite a late start, their efforts to save North America’s ash trees will be successful.
The woods we have at Mary Virginia Crites Hannan Park did not escape the EAB invasion. Many of our ash trees have died or are dying. Perhaps you have lost ash trees in your yards and neighborhoods. The Friends of the Circleville Parks are hosting a tree identification program called “What Tree Is That?” on Saturday, Aug. 17 at 10 a.m. in the Starkey Pavilion at Mary Virginia Crites Hannan Park, 1230 Pontius Road in Circleville.
Our presenter, Paul Hang, is an Ohio Certified Volunteer Naturalist and a Master Gardener Volunteer. Paul will teach participants how a MAD BUCK can help them identify the trees in their yards and in the forest. Children 12 and younger are welcome but must be accompanied by an adult.
For further information, please contact Brenda Johnson at 740-497-0119, Melanie Shuter at 740-601-4907 or Paul Hang at 740-497-4397.
Brenda Johnson is an Ohio Certified Volunteer Naturalist.