New Invasive Wood Wasp Found in Michigan

By MSU Staff
August 1, 2007

An exotic wood wasp, Sirex noctilio, has made its way to Michigan, reports Deb McCullough, MAES forest entomologist.

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"The wasp was recently captured in a trap in Macomb County," McCullough said. "The larvae of this insect feed in stressed, dying or recently killed pine trees. Sirex noctilio has been an important pest in pine plantations in Australia, New Zealand and some South American countries."

McCullough said the wood wasp is native to Europe, Asia and North Africa but was discovered in New York in 2005 and in Ontario in 2006.

"Like many other wood-boring insects, it probably came to North America in solid wood packing material, and it was likely present for several years before it was discovered," she said.

The discovery of Sirex has led to claims by many residents that their trees may be infested with the pest. There are some important aspects of the Sirex noctilio capture in Michigan that residents need to know about before they claim they have seen it or have trees infested with the pest.

"First, horntails, including Sirex noctilio, are related to wasps," McCullough said. "Horntails can look very similar to wasps, and many people will likely mistake the bluish black wasps that they see around their homes for horntails.

"Second, 23 species and subspecies of horntails are native to North America," she added. "Some species colonize pines or other conifer trees. Other horntail species colonize hardwood trees -- beech, for example, is a common host. Virtually all horntails are some combination of yellowish brown or black, and they all look alike. Even entomologists have a difficult time trying to distinguish one species from another. Native horntails are not considered a problem. Because they colonize dying or recently dead trees, they play an important role in decomposition and nutrient cycling."

Whether Sirex noctilio will become an important pest of pine in Michigan or other areas of North America is yet to be determined, McCullough said.

"We have many insect species that colonize stressed, dying or recently killed pines," she said." Sirex wood wasps will have to interact with and compete with those native insects for that same pine resource. In addition, we do not yet know if Sirex noctilio is established in Michigan or if the insect collected in the trap was simply dispersing from an infestation in Ontario. Wood wasps are very good fliers, and it's quite possible this particular insect originated in Ontario. Many traps were set in Michigan this year for Sirex noctilio following the identification of the infestations in Ontario last year. After horntail flight ends (late summer) and once all the horntails collected from traps or trap trees have been identified, we'll have a much better idea of whether Sirex noctilio is actually established in Michigan."

She also noted that Sirex noctilio will face native natural enemies in North America and possibly an introduced biological control. At least two groups of native parasitoid wasps will attack horntail larvae. In addition, an active biological control program developed in Australia makes use of parasitic nematodes. Methods have been developed to inoculate pines and introduce the nematode into Sirex noctilio populations. Research is under way in the United States to assess potential non-target effects of the nematode. If results indicate that the nematode can be safely released, the methods developed in Australia will likely be used to establish the nematode in Michigan.

Last Updated: 11/24/2007