Taking a stand for trees: rebuffing the emerald ash borer

Life cycle of the emerald ash borer

• Female ash borers lay 40+ eggs in the bark of an ash tree.
• Eggs hatch in two weeks. Larvae emerge, then feed below the bark for 1–2 years, creating S-shaped "galleries”—this is the most destructive stage.
• Larvae then pupate, after which they turn into adults.
• Adults emerge through D-shaped holes in the bark.
• The adults mate, find another tree, and start the process over.
• The host tree will likely be dead in three to five years.

Marshaling microbes

The emerald ash borer, or EAB, can be stopped by removing ash trees from a vicinity in advance and planting other species. This method is costly in time, money and, often, emotions. Enlisting armies of biological agents to attack the insect will avoid these drawbacks.

But even if infestation and tree loss or removal looks inevitable, “We want to develop another tool for land managers to slow EAB down so they can have a smoother transition,” Blanchette says.

In Blanchette’s lab, graduate student Colin Peters researches fungi that infect insects. His work is geared to protecting black ash, a tree that forms an immense forest in northern Minnesota. The black ash is central to several Indigenous cultures, to whom it is important for making baskets or as a spiritual resource and source of medicine.

Friendly fungi

Peters is also experimenting with injecting the fungus into ash trees, where it can live without killing the trees.

“The fungus has genes similar to genes that help bacteria infect guts of insects,” he explains. “I inject roots, the fungus moves up into the tree, then EAB larvae feed on the cambium and phloem and ingest the fungus.”

Stop signs for invasive fungi

In other work, Blanchette and graduate student Nick Rajtar are collaborating with the state Department of Agriculture and 40 businesses—nurseries and Christmas tree plantations—to detect and prevent the spread of invasive waterborne molds.

“Minnesota ships nursery material in from other states, so we’re surveying state nurseries to identify introduced pathogens as early as possible,” Rajtar says. “We know there are 14 new-to-the-state species. Some are very pathogenic against rhododendrons, oaks, alders, and woody domestics.”

Blanchette’s group is also part of a project to thwart the spread of a root fungus deadly to red and white pines, as well as other conifers. Dozens of spore traps have been set up along the Minnesota-Wisconsin border to detect any of the fungus coming in from the east.

“It was found near Winona in 2014, but so far, the state Department of Natural Resources (DNR) has been able to eradicate it,” Blanchette says.

Secret sauce of success

"The Minnesota Terrestrial Plants and Pests Center (MITPPC) and Minnesota Aquatic Invasive Species Center (MAISRC) are unique—we focus on invaders that are the greatest threats to the state," says Robert Venette, director of the MITPPC and adjunct associate professor in the Department of Entomology. "Prioritization is the ‘secret sauce’ that makes both centers work. We concentrate resources where they’ll make the biggest impact."

That's one reason “the University of Minnesota is a national leader for research on invasive species,” he says.

Minnesota is meeting the challenges of EAB and other plant pathogens because it has invested in the places best suited to the task. As Blanchette puts it:

“It’s taken the University’s expertise to put together projects so we can control invasive species before they cause enormous damage to our natural resources.”