Hopeful News About Emerald Ash Borer

 “Attack fungi” could help manage this destructive insect.

University of Minnesota researchers recently discovered insect-attacking fungi in the larval galleries of emerald ash borer. Their finding offers hope that the fungi could help manage this destructive pest.

Emerald ash borer (EAB) is an introduced beetle that kills all species of ash trees. It has been present in the U.S. since at least 2002 and in Minnesota since at least 2009. Even with a federal quarantine (now removed), the insect spread rapidly. According to the USDA, its range now covers most of the eastern U.S. and the Midwest, with isolated infestations as far west as Colorado.

The larvae of EAB cause the bulk of the damage. After eggs hatch, the larvae bore into the inner bark, the area that includes the water- and sap-conducting cells of the xylem and phloem. Their galleries of serpentine tunnels interfere with the flow of needed resources and kill trees in 2-4 years. Hundreds of millions of trees have succumbed to the insect.

Hope for managing EAB rests in part on biocontrols, organisms that prey on eggs, larvae or adults and so reduce their numbers. Three parasitoid wasps have been released in Minnesota as potential biocontrols. More information about that program is available here.

New biocontrols could emerge from recent research by the Minnesota Invasive Terrestrial Plants and Pests Center (MITPPC). In their study published in Fungal Biology, U of M researchers sampled affected trees from Rochester to Duluth and isolated the fungi associated with EAB larval galleries. They identified many types of fungi, including some that are entomopathogenic – fungi that attack insects.

One fungus they identified, Beauveria bassiana, has already been studied for EAB control. The other entomopathogenic fungi they found also need research to see if they, too, could be used to manage the insect.

This good news comes as EAB continues to spread in Minnesota. Since the November 2020 post about EAB, the insect has been confirmed in two more counties, Cottonwood and Blue Earth in southwest Minnesota. The state’s Department of Agriculture maintains a quarantine boundary that now includes 27 affected counties.