Emerald Ash Borer and its Enemy Wasps

Since emerald ash borer was first detected in Michigan in 2002, the non-native invasive beetle has killed tens of millions of ash trees across the U.S., and continues to infest new regions, including Great Smoky Mountains National Park.

Within its native range in Asia, emerald ash borer is attacked by a variety of predators including several species of parasitoid wasps that specialize on the beetle’s eggs or larvae. Because these wasps are expected to play a role in maintaining low emerald ash borer populations in Asia, three species have been introduced into North America as biocontrol agents. “There is great interest in knowing how effective these introductions have been in reducing the population growth rates of emerald ash borer in North America,” says U.S. Forest Service Southern Research Station (SRS) scientist Michael Ulyshen.

In addition to the introduced biocontrol agents, some native wasps have also been shown to parasitize emerald ash borer larvae, and birds – especially woodpeckers – eat the larvae and pupae. From 2007 to 2010, the researchers released thousands of non-native predatory wasps in experimental release plots in forests of southern Michigan.

Both native enemies and introduced parasitic wasps play important roles in suppressing emerald ash borer populations. Non-native parasitic wasps can help prevent widespread ash tree death in newly infested forests, and the scientists recommend that they be released as soon as the presence of emerald ash borer has been detected. The non-native wasps also keep emerald ash borer populations low in forests that have already been invaded.

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