Scientists on the Trail of Pine-Killing Wasp

By Marcia Goodrich | Published

Scientists have found another exotic bug in Michigan that eats native trees, but at this point, it appears that the sirex woodwasp won’t cause quite the same devastation as the emerald ash borer.

In part, that’s because Sirex noctilio, a native of Eurasia, probably only attacks trees that are already stressed, says Andrew Storer, an associate professor in the School of Forest Resources and Environmental Science. “It is also possible that an important biological control agent of the woodwasp has arrived with it—a nematode worm that parasitizes the wasp larvae and sterilizes the adult female,” he said.

“We already have a whole suite of insects that attack pines, and at this point, we don’t know how the sirex woodwasp will affect them,” Storer said. “It will be important to evaluate the impacts of this new player in our different forest ecosystems.”

The woodwasp damages and kills two- and three-needled pine trees, including Austrian, jack, red and scotch pines. In Michigan, red pines are a significant source of timber, and jack pines are critical habitat for the endangered Kirtland’s warbler.

Sirex woodwasps have found their way all over the world in wood packing materials and have destroyed up to 80 percent of the pine trees in some plantations. When the female wasp lays her eggs in the wood of host trees, she also injects a toxic mucous and a fungus. Acting together, the mucous and fungus mortally wound the tree, making a suitable environment for the wasp larvae to tunnel in the wood.

Sirex woodwasp was recently detected in Macomb County in a trap set by the US Department of Agriculture, Animal and Plant Health Inspection Service. It has previously been detected in New York state and Ontario. Storer is part of the team working to determine what areas in Michigan are infested. The team includes the US Department of Agriculture, the Michigan Department of Agriculture, the Michigan Department of Natural Resources and Michigan State University, as well as Michigan Tech.

Michigan Tech has about six scientists and technicians working on the detection and delimitation project. At over 100 sites around the state, pine trees are stressed by treating them with herbicides, and traps are set to catch woodwasps attracted to the weakened trees. “Delimiting the area infested by this insect and screening trapped insects for the nematode worm are important first stages in responding to this new exotic pest in Michigan,” says Storer.

More information on the sirex woodwasp is available at

Michigan Technological University is a public research university, home to more than 7,000 students from 60 countries. Founded in 1885, the University offers more than 120 undergraduate and graduate degree programs in science and technology, engineering, forestry, business and economics, health professions, humanities, mathematics, and social sciences. Our campus in Michigan’s Upper Peninsula overlooks the Keweenaw Waterway and is just a few miles from Lake Superior.