The soon-to-be published study is the first to document the invasive beetle's rate and distribution of spread from its epicentre in the Windsor-Detroit area.
"In the Great Lakes region this beetle invasion is mushrooming out like an atomic bomb going off," says the study's co-author Dr. Hugh MacIsaac, an expert in invasive species at the University of Windsor's Great Lakes Institute for Environmental Research.
The small, metallic green beetle – adults are about the length of a thumbnail – was first detected following an unusual dieback of ash trees in southeastern Michigan and southwestern Ontario in the summer of 2002. A native of southeast Asia, the insect is capable of rapidly spreading with a little human help. Adult beetles lay eggs under tree bark and the feeding larvae kill trees by disrupting the flow of nutrients in the soft tissues under the bark.
The new study funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) reveals that unprecedented actions taken to stop the borer's spread have so far failed to halt its outward march. At risk are nine billion ash trees in the United States and Ontario, with an estimated value of more than $300 billion in the United States alone.
"Its distribution continued to spread during 2005 in the Great Lakes region despite extensive containment, quarantine and eradication measures," write the authors, including Ken Marchant, a lead emerald ash borer expert at the Canadian Food Inspection Agency (CFIA).
Since 2002, all areas in Michigan and Ontario known to be infected with the borer are under quarantine. Prominent signs along highways advise the public of the total ban on the transport out of the area of ash trees, saplings and firewood. During the winter of 2003-2004, the CFIA took the dramatic step of creating a borer "firewall" in Ontario's Essex County. That involved removing all the ash trees in a ten kilometre wide swath between lakes Erie and St. Clair, beyond the eastern boundary of the borer's current range.
Regardless, the report notes, "the borers distribution expanded dramatically in 2004" primarily through natural dispersal, but in some cases through human transport. In Ontario, the borer infected 23 new sites to the east, all beyond the firewall. The study suggests that the new infestations most likely came from infected firewood or saw logs moved there prior to the creation of the firewall – but MacIsaac doesn't rule out the possibility that beetles jumped the ash-free zone. The study notes that scientists still need to determine the maximum flight potential of adult borers.
In Michigan, the borer was reported at 29 new sites in 2004. New infestations were also reported in Ohio and Indiana.
The one bright spot in the study is the apparently successful eradication of a borer population that was introduced into Maryland and, subsequently, into Virginia in a shipment of infected nursery saplings from Michigan. Officials destroyed the saplings as well as all ash trees within a kilometre of each infected site.
"The success in Maryland shows that if you get them early and before they build up large populations you can probably extinguish colonizing groups," says Dr. MacIsaac, whose research is primarily on freshwater and marine invasive species. Scientists believe the borer probably entered North America in ash shipping materials, and was present for as much as a decade prior to being identified.
The challenge in the Great Lakes region, he says, is the current extent of the infestation. The infected zone now covers all of Ontario's Essex County and extends to include the entire lower peninsula in Michigan and much of northern Indiana and Ohio.
"It's not just an Ontario or Canadian problem. Even if we're able to contain it here, it could come across at Sarnia or at Sault Ste. Marie. It's a case where we need, and are getting, international cooperation," says MacIsaac, noting that the American and Canadian governments are making extraordinary efforts together.
The 2005 federal Canadian budget contained the first line item ever to target invasive species directly – $85 million, much of which is earmarked for battling the borer and another forest pest, the Asian longhorn beetle, which has infected hardwood trees in areas around Toronto, New York and Chicago.
If containment isn't effective, MacIsaac knows well what the future will look like. He arrived at his Windsor-area home one day in the summer of 2003 to see a neighbour cutting down 25 ash trees, among the borer's first victims. In Michigan's Wayne County, the first area infected, 60 per cent of the ash trees are already dead.
"In my opinion, the prognosis does not look good in the Great Lakes region," says Dr. MacIsaac. "If containment doesn't work, we are going to see a repeat of Dutch elm disease, which wiped-out a dominant forest tree species from eastern North America."
Dr. MacIsaac's paper on the beetle will be published in a forthcoming issue of Diversity and Distributions.
Contact: Dr. Hugh MacIsaac 519-253-3000 x3754 (office); x 2734 (lab); 519-817 9689 (cell); e-mail: hughm@uwindsor.ca
Learn more about Dr. MacIsaac's research at: http://www.uwindsor.ca/hughm.
For background information on the emerald ash borer and Canadian and U.S. efforts to slow its spread visit the Canada Food Inspection Agency at: http://www.inspection.gc.ca/english/plaveg/protect/pestrava/ashfre/agrplae.shtml.
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The study was funded by various agencies including the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canada Foundation for Innovation (CFI) and the Department of Fisheries and Oceans, which funds Dr. MacIsaac's Invasive Species Research Chair.
Abstract from "Modeling local and long-distance dispersal of invasive emerald ash borer Agrilus planipennis (Coleoptera) in North America"
Limiting damage by non-indigenous species requires rapid determination of current and potential distributions, vectors of dispersal, and development of appropriate management measures. The emerald ash borer (Agrilus planipennis), a wood-boring beetle native to Southeast Asia, was first reported in the Great Lakes region during summer 2002. The beetle poses an enormous threat to native ash (Fraxinus) species of North America, as untreated trees in infested areas of Ontario, Michigan and Ohio suffer high mortality. We demonstrate that the borer has spread in North America through a combination of diffusive range extension, associated with local flights, and by long-distance 'jump' dispersal associated with human movement of infected ash saplings or contaminated firewood. Probability of infestation was inversely related to distance from borer epicenters but positively related to the size of human population centres. At least 9 of 39 populations that were first reported in Michigan during 2004 cannot be accounted for by local diffusion, raising the possibility that other unidentified mechanisms may be contributing to dispersal of the beetle. Absent quarantine, by 2005 all of Michigan's lower peninsula was contained within the boundaries of potential diffusive range expansion. Infected ash saplings also were introduced from Michigan to Maryland during 2003, and subsequently transplanted to five sites in Maryland and Virginia. Quarantine and eradication measures have had mixed results: in the south-central USA, the species appears on the brink of eradication, whereas its distribution continued to spread during 2005 in the Great Lakes region despite extensive containment, quarantine and eradication measures. Quarantine success in the Great Lakes region is encumbered by multiple dispersal vectors, and by larger population sizes and the more extensive geographic distribution that was achieved prior to implementation of control measures.
Journal
Diversity and Distributions