Canada Approves Release of Tiny Wasps to Kill Emerald Ash Borer

Ottawa, Canada (June 5, 2013) – The Canada Food Inspection Agency has approved the release of two tiny wasps from China to eat the tree-killing emerald ash borer, which has no natural enemies in North America. A eulophid wasp and a braconid wasp were both approved. This policy announcement comes on the heels of recently published U.S. Forest Service/Michigan State University lab and field research suggesting these natural enemies will likely play a critical role in suppressing the EAB.

emerald ash borerEulophids are a little over a millimetre long, while braconids very slightly larger. Both lay their eggs inside other insects such as moths, butterflies and beetles. The young wasps hatch and eat their way out of the host insect, killing it.

According to a CIFA representative, the wasps won’t kill every beetle but should bring them back to a level where they become a manageable presence in the environment.

These wasps come from northern China, the region from which the EAB was probably brought to North America. The EAB, a relatively new invasive insect pest, has killed tens of millions of ash trees throughout the eastern U.S. since it was first detected in 2002 in Michigan and Canada.

There are many types of both eulophids and braconids; the types approved now are called Tetrastichus planipennisi and Spathius agrili. A third candidate won’t be released because there isn’t enough information to know whether it would be harmful to other insects.

Until now, the only defense against the ash borer has been to inject a beetle-killing chemical into each tree at two-year intervals, a slow and expensive process.

To control the EAB, research on its natural enemies was initiated shortly after its discovery, resulting in a classical biological control program using three parasitoid wasps native to northern China, where the EAB populations in the U.S. likely originated.

After research on the biology, laboratory rearing, and host specificity of the three parasitoid species was completed in 2007, U.S. federal and state regulatory agencies approved their environmental release in more than a dozen states.

In an article appearing in the June issue of the Journal of Economic Entomology, the authors observed one of the species, Tetrastichus planipennisi Yang, and found that the populations of these parasitoid wasps have been increasing and expanding in Michigan, which suggests that they will likely play a critical role in suppressing the EAB in that state.

Researchers sampled trees for wasp broods at six forest sites near Lansing, Michigan. By the fall of 2012, the proportion of sampled trees with one or more broods of T. planipennisi increased from 33% to 92% in the plots where the wasps were released. Similarly, the rates of parasitism on the EAB increased from 1.2% in the first year after the parasitoid releases to 21.2%. These tiny wasps, which do not sting humans, lay eggs into or on the EAB larvae.

Importing one non-native species to kill another is called biological control, but it brings risks. The main one is that the species brought in as a savior starts feasting on plants or animals that we don’t want it to eat, or that its population spirals out of control.

The wasps, which were brought in to and went through screening in the U.S., have just gone through the regulatory system in Canada.

Related Resources
Chinese Wasps are Taking on the Emerald Ash Borer (Links to Journal of Economic Entomology, “Establishment and Abundance of Tetrastichus planipennisi (Hymenoptera: Eulophidae) in Michigan: Potential for Success in Classical Biocontrol of the Invasive Emerald Ash Borer (Coleoptera: Buprestidae)”
Approved: Tiny wasps that kill emerald ash borer
Emerald Ash Borer Meets Its Nemesis