by Catherine Krikstan
March 30, 2016
Less than 15 years ago, an exotic green beetle was discovered in southeastern Michigan. In the years that followed, the metallic insect that is no more than half an inch long spread into 24 more states—including five in the Chesapeake Bay watershed—and now threaten millions of native ash trees that fall sick and die when the insect’s larvae feed on the tissue underneath their bark.
The emerald ash borer likely arrived in the United States on wood packing material carried on airplanes or cargo ships from its native China. While the insects can fly at least half a mile from where they emerge as adults, it is the movement of larvae-laden wood that is thought to be the cause of many emerald ash borer infestations. As a result, the shipment of ash trees and logs is regulated, and transporting firewood outside of quarantined areas is illegal.
Such precautions are necessary because of the impact the emerald ash borer can have on forests. As larvae feed on the nutrient-rich inner bark of ash trees, they disrupt the trees’ ability to move food and water from its roots to its leaves. Once a tree is infested with emerald ash borer larvae, one-third to one-half of its branches may die within a year. Most of its canopy may be dead within two years, with the entire tree dead in three to four.
Ash trees can be found in almost all parts of the United States. All North American ash trees are susceptible to infestation, which means countless forests are susceptible to the loss of a species that supports the ecosystem’s protection of clean air, water and wildlife habitat. While native trees could fill the gaps left by dead ash, invasive plants could also spread in response to new light levels. Even the makeup of the surrounding soil may change, as ash trees are “dynamic accumulators” that gather calcium from the soil around them.
The economic impacts of the emerald ash borer are significant. First, there are costs to losing trees. The U.S. Forest Service estimates the eight billion ash trees on U.S. timberlands to be valued at $282.25 billion. Then, there are costs to mitigating the damage the insect has done. The Forest Service has predicted that an expanding infestation through 2019 will warrant the treatment, removal and replacement of more than 17 million ash trees, with an estimated price tag of $10.7 billion.
But the Forest Service has also explored an impressive number of emerald ash borer control and management methods. Experts have searched for effective predators, parasitoids and pathogens that could act as biological controls, evaluated the efficacy of insecticides injected into trunks of infested trees and explored the development of genetic hybrids that would integrate the resistance of Asian ash tree species into those native to North America. Experts have also conducted research into ridding trees of larvae by submerging infested logs under water, treating infested logs with chemicals and removing the bark of infested logs that could otherwise be sent to sawmills and manufacturing plants to be used for lumber, railroad ties and other value-added products.
In light of the extensive research that has been done in the years since the emerald ash borer was first found in the United States, the most important thing for individuals to remember is to follow regulatory guidelines for moving ash trees, logs and firewood and to report potential infestations to your local Cooperative Extension Service office. According to the Forest Service, making a large investment in understanding and controlling the spread of this invasive insect now could slow the expansion and postpone the ultimate costs of the emerald ash borer.