The Gardener’s Corner: Emerald Ash Borer Strategy

June 20, 2013 · 0 Comments

The Canadian Food Inspection Agency has approved the release of two tiny wasps from China to eat tree-killing beetles which have no natural predators in North America.

The emerald ash borer is eating its way through our ash trees and in many places, they have been cut down to stop the insect.

The Agency has approved both a eulophid and a braconid wasp which are so tiny, they’re barely visible. They lay their eggs inside other insects such as moths, butterflies and beetles. The wasps hatch and then eat their way out of the host which kills it.

It is expected to be an acceptable long term strategy of control for ash borers to bring them back to a manageable level in the environment.

Until now, the only defense against ash borers was the slow and expensive process of injecting a beetle killing chemical into each tree every two years.

Michigan, which has been battling this pest longer than Ontario reports that testing with the wasps there has been successful. The wasps have formed fast growing populations which have parasitized an increased percentage of the borers over a five year study.

The borers actually first appeared in Michigan back in 2002. They lay their eggs under the bark of all varieties of ash and the immature beetle tunnels under the bark.

This destroys the part of the tree that intakes water and nutrients, causing it to die.

Biological control is when one non-native species is brought in to kill another. Sometimes there is a risk that the restraining species will spiral out of control but the Canadian Ministry of Agriculture has likely done extensive research on what these wasps are interested in through testing their life cycles .

The photo is from a gardening associate who is also an arborist. He notes that in the fall, the tree in question showed no visible signs of borers or decline. By April of this year the whole trunk was riddled with holes. Apparently woodpeckers discovered the borer larvae over winter and made their own holes in the bark to extract the food.

The cut out section clearly shows the damage done by so many larvae feeding on the tree.

By Judith Rogers