SOUTH HURON – Two Ausable Bayfield properties near Exeter are the first sites in Canada to be chosen for new research into biological control of an invasive beetle species that is killing ash trees.
As the emerald ash borer (EAB) continues to spread across Ontario, researchers from the Canadian Forest Service have selected two sites in the Hay Swamp area, west of Exeter, for their research into management of populations of the damaging insect.
The EAB infests all native species of ash and the trees are dying. Native predators, parasites, and diseases have been unable to prevent infestation. Native ash species have also shown very little resistance or tolerance to the EAB pest, which was accidentally imported from Asia to North America.
The borer was first discovered to be killing ash trees in the Windsor-Detroit area in the early part of the 21st century. The invasive beetle was first detected in the Ausable Bayfield watershed area in 2008, near Bayfield, and it is moving across the watershed. “This summer I am really seeing the effects of the borer in areas where I didn’t see it last year,” said Ian Jean, the forestry specialist with Ausable Bayfield Conservation Authority (ABCA). “You can really see the thinning crowns on the ash trees, especially as I drive south and west of Exeter, and in the Bayfield River corridor.”
“We have had ideal tree growing conditions this year but obviously not enough to offset the effects of the borer,” he said.
Gene Jones and Dr. Barry Lyons, of the Canadian Forest Service, are Canadian researchers studying biological control of EAB. Jones contacted ABCA staff in the spring looking for candidate study sites. Suitable study sites included a high proportion of ash as well as light to moderate infestation of EAB. Two sites on Ausable Bayfield property at Hay Swamp met their study criteria.
“Hay Swamp is our largest natural area and has a high component of ash,” Jean said. “Before Dutch elm disease, Hay Swamp had large elms. We have lost the large Elm trees and we expect to lose all of the large ash over the next few years. Ash is such an important species for timber and wildlife, especially in our swamp forests.”
The study will look at the effect of introducing a parasitic insect (or parasitoid) called Tetrastichus planipennisi. This insect is native to North Asia and it is a parasitoid of the EAB. Parasitoids are a type of insect that consume and kill hosts and that’s why this species is a potential management tool for EAB.
“This is an opportunity to host some important research,” Jean said. “This won’t solve the emerald ash borer problem in the short term but it may be very helpful over the long term.”
Biological control is one of the strategies that has been investigated since the scope of the infestation was realized. The search for biological control agents began in 2003 with a partnership between United States Department of Agriculture and the Chinese Academy of Forestry. Their research identified Asian parasitoids as candidates for biological control in North America. Three parasitoids were released at five sites in Michigan in 2007. A biological control production facility was established by the United States Department of Agriculture in Brighton, Michigan in 2009 to produce the Asian parasitoids. Since then, more than 440,000 EAB parasitoids have been released in at least 12 states.
The Canadian Food Inspection Agency recently approved the importation and release of one of the Asian EAB parasitoids, Tetrastichus planipennisi, produced in Michigan, for research in Canada. This parasitoid was approved because it has high degree of host specificity on the EAB. Tetrastichus planipennisi is a larval parasitoid of EAB from China, where it attacks and parasitizes up to 50 per cent of EAB larvae in some areas. The female parasitoid lays eggs inside EAB larvae where the parasitoid larvae grow, eventually killing their host. The parasitoids are reared in Michigan and transported to Canada in small ‘bolts’ of wood about four inches long.
Tetrastichus planipennisi was released at the study sites in June with another release planned for August to September.
The American biological control studies have shown some promise. According to media reports, a Michigan study has found that the number of EAB beetles that were ‘parasitized’ grew from 1.2 per cent in the year when wasps were first released (2007) to 21.2 per cent last year.
When the borer was discovered in Canada, the Canadian Food Inspection Agency focused initially on containment of the pest through a program of quarantine zones. This effort to slow the spread of the borer was in part to create enough time for researchers to learn more about the borer and how to best manage the pest.
It is the larval stage of the borer feeding on the cambium (a thin layer of actively dividing cells under the bark that produce the inner bark and the outer wood) of the tree that causes trees to die, Jean said.
“Each borer feeds in an area about the size of the palm of your hand,” he said.
A tree wouldn’t even notice a few borers feeding on it. The problem is that, over the period of a few years, the population builds up to hundreds or more borers on a single tree, to the point that the vascular system of the tree is severely damaged. The tree can no longer transport enough water to the crown or food to the roots and it slowly dies.