Emerald ash borer solution? Parasitic wasps

The emerald ash borer adult is a green buprestid or jewel beetle about half inch long. (Provided photo — Dr. James Zablotny; USDA APHIS)

The emerald ash borer (EAB) is a half-inch long, green buprestid or jewel beetle. It’s an invasive insect native to Asia, believed to have made its way to the United States on solid wood packing material carried in cargo ships or on airplanes.

EAB was first discovered in the U.S. in 2002, near Detroit, Michigan. Around that time, it was also found across the Detroit River in Windsor, Ontario, Canada. In 2003, the U.S. Department of Agriculture Animal and Plant Health Inspection Service initiated a domestic quarantine program for areas infested with the extremely destructive wood-boring pest of ash trees, but the insect still managed to progressively advance and expand its range.

EAB is now present in 35 states, the District of Columbia, and five Canadian provinces and is responsible for the destruction of hundreds of millions of ash trees in forests, rural areas, and urban and suburban landscapes. It has become the most destructive and costly invasive forest insect in North America.

States in the eastern U.S. produce nearly 114 million board feet of ash saw-timber annually, with a value of more than $25 billion. The compensatory value of the 8 billion ash trees on U.S. federal, state, and private forest land potentially infested with EAB is estimated to be $282 billion.

EAB in New York

EAB was first discovered in New York state in the spring of 2009, after two USDA Agricultural Research Service employees recognized damage to ash trees in the town of Randolph in Cattaraugus County. The infestation was reported by Rick Hoebeke, a senior Cornell Cooperative Extension associate who served as the assistant curator of the Cornell University Insect Collection from 1977 to 2011. The presence of EAB has now been confirmed in all New York counties except Essex, Hamilton, Lewis and Washington. The state Department of Environmental Conservation continues to work with CCE to detect and confirm new infestations across the state.

Most EAB infestations are started by unknowingly moving infested firewood, nursery trees or saw logs. So, in an effort to limit the potential introduction of the beetle into other areas of the state, the DEC initiated regulations which placed infested counties under quarantine and initiated eradication activities in quarantined areas. The quarantines restricted the movement of ash trees, ash products and all species of firewood.

Regulations changed

While the DEC continues to collect new EAB location information, it is no longer actively managing EAB infestations. This course of action evidently stems from a December 2020 APHIS ruling removing all federal domestic EAB quarantine regulations. The DEC’s mandate restricting the movement of firewood of any tree species to within 50 miles of its source or origin remains in effect however, and best management practices recommendations for moving ash logs have been established. If you must move ash wood that is not firewood, please learn more about and be sure to follow DEC guidelines. New York has more than 900 million ash trees, representing about seven or eight percent of the trees in the state. And all are at risk.

Parasitoid wasp

In preference to regulating containment, APHIS has been redirecting its focus toward what researchers have determined will be a more effective, more sustainable and less intrusive long-term method for EAB management. Biological control is the practice of importing and releasing natural enemies from a pest’s native range to help manage the target-pest’s populations in areas of introduction. APHIS research into natural enemies of EAB has identified several species of small, female parasitoid wasps that don’t bite or sting, but which seeks out EAB, in order to lay their eggs inside the bodies of living EAB larvae. When the wasp eggs hatch, the developing wasp larvae feed on their living hosts; ultimately killing them. One tiny species of wasp lays its eggs within the eggs of the beetle, killing the host egg.

To date, APHIS, along with numerous state, county, tribal and academic partnering agencies, has released more than eight million of the parasitoid wasps in 30 states and the District of Columbia. Offspring have been recovered in 22 states, indicating that the wasps are successfully establishing, reproducing and killing EAB. APHIS rears the wasps at a facility in Michigan and ships them to their partners, who then release the parasitic bio-control agents into areas where EAB is infesting ash trees. Because this strategy focuses directly on the ash boring insect, it’s widely acknowledged as a very promising course of action for reducing EAB populations and protecting North American ash trees.

In 2013, the U.S. Forest Service began providing wasps to the Canadian government. Natural Resources Canada is now productively rearing wasps at a laboratory in Sault Ste. Marie, Ontario, for use in their own EAB bio-control program.

USDA’s bio-control goal is to stabilize and eventually reduce EAB populations by initially releasing the parasitoid wasps into every county with a known EAB population large enough to sustain the wasps and then expanding the distribution and increasing the number of wasps released in EAB-infested states. Wasps have already been released in several New York counties, including Clinton, St. Lawrence and Jefferson.

Whether the introduced parasitoids can regulate EAB populations at low enough densities to facilitate long-term survival of ash regeneration remains to be seen.


Today's breaking news and more in your inbox

I'm interested in (please check all that apply)
Are you a paying subscriber to the newspaper? *

Starting at $4.75/week.

Subscribe Today