12/15/2003

How Fast Can Emerald Ash Borer Spread?

Writer:

Mauricio Espinoza
espinoza.15@osu.edu
(330)202-3550

Source:

Dan Herms
herms.2@osu.edu
(330)202-3506

WOOSTER, Ohio -- The recent discovery of emerald ash borer (EAB) in central Ohio has sparked new questions and worries about the insect’s dispersal capabilities and the extent of the infestation in Buckeye country. But according to Ohio State University scientists, while the threat to the state’s ash trees is real, there’s no reason for citizens to be alarmed.

“Ohio is not being overrun by emerald ash borer,” said Dan Herms, an entomologist with the Ohio Agricultural Research and Development Center (OARDC). “Although it does pose a clear threat to ash in Ohio, the current infestations are very small and isolated. Excluding the infestation in the town of Hicksville (which has been established for several years), there are currently less than 50 trees known to be infested in the entire state.”

Accidentally imported from Asia and first spotted July 2002 in Detroit, the wood-boring beetle has been found this year in the northwestern Ohio counties of Lucas, Wood, Defiance and Paulding.

The first confirmed infestation outside of that area -- which is adjacent to the core infestation in southeast Michigan, where more than 6 million ashes are dead or dying -- was confirmed Dec. 1 in Columbus and has been linked to nursery stock imported from Michigan in 2001, before EAB had been identified in North America.

Thus far, all Ohio infestations have been caused by movement of ash materials into the state. But the question remains just how far and how fast EAB can fly and spread on its own.

Research conducted by OARDC in cooperation with the U.S. Forest Service and the Canadian Forest Service has found that EAB has the physiological capability to fly up to six miles in a 24-hour period. These studies were carried out in the lab with the use of flight mills. In the field, however, the beetle spreads at a much slower pace.

“One of the major questions surrounding the eradication program is how far will the insect disperse, which determines how wide of an area eradication programs have to focus on,” Herms said. “Although lab studies indicate emerald ash borer has the potential to fly several miles when forced repeatedly to fly to exhaustion, field analysis of infestations in Ohio indicate that the insect is spreading at a rate of less than one-quarter mile per year.”

Ohio’s EAB eradication program is using this spread rate as a guideline. Last April in Whitehouse (Lucas County), the Ohio Department of Agriculture cut and destroyed 8,000 ash trees within a quarter mile of the infestation point. An additional 100 trees within a half mile of the infestation were treated with the insecticide imidacloprid as a preventive measure.

“The Lucas County eradication program provides every indication that emerald ash borer can be successfully eradicated from Ohio, especially given the small, isolated nature of the current infestations,” Herms said. “Eradication of the core infestation in Michigan will be more challenging, but it is possible.”

Herms added that even if the core infestation in Michigan is not successfully wiped out, the eradication program will significantly slow its spread, resulting in very gradual colonization of Ohio ashes over a number of years. “This will provide ample time to anticipate and plan for the arrival of the infestation,” he said.

The Ohio Emerald Ash Borer Task Force -- of which Herms and OSU Extension entomologist Dave Shetlar are members -- is making recommendations on how to proceed with eradication efforts in the remaining infestation sites next year. Eradication will take place before mid-May, when overwintering EAB larvae emerge and fly to lay eggs on new trees.

OARDC and OSU Extension are part of Ohio State’s College of Food, Agricultural, and Environmental Sciences.

Editor: For photographs of emerald ash borer, infestation symptoms and Ohio's EAB surveillance and eradication efforts, contact Ken Chamberlain, (330) 263-3779 or chamberlain.1@osu.edu.