Researchers, local park boards – and fungi – come together to fight the emerald ash borer in Minnesota.
August 28, 2019
Since 2002 when the emerald ash borer (EAB) was first identified in Michigan, the insect has become something of a poster child of terrestrial invasive species in the central and Great Lakes region of the US.
EAB is a wood-burrowing pest whose larvae target all North Amerian ash trees (Fraxinus spp). This feeding can cause a rapid decline in tree health, resulting in death in anywhere from 1-4 years depending on a tree’s size and initial health.
The pest threatens an estimated 1 billion ash trees across Minnesota. That risk also extends to urban green spaces, where ash can make up more than half of a city’s tree population.
MITPPC-funded researchers led by biologists Robert Blanchette and Kathryn Bushley are now taking an innovative approach to EAB management by exploring the fungal communities associated with infestation. The team is hoping to identify fungi that degrade ash wood after infestation, along with any fungal species that could naturally control EAB.
Emerald ash borer larvae feed on ash wood and leave visibly destructive 'galleries' behind. (Credit: Caro Silvola, MITPPC)
A preserved emerald ash borer larva specimen, Agrilus planipennis. (Credit: Caro Silvola, MITPPC)
Ash under attack
As it turns out, wood decay-causing fungi are likely a large part of the reason for ash trees’ speedy decline following EAB infestation. Decaying ash trees pose a serious safety risk to bystanders and arborists who hope to remove infested trees, as they are prone to easy toppling.
“We hypothesized that these fast-growing decay fungi get in because the EAB is creating a wound in the tree,” said Benjamin Held, a research scientist working on the project. “These fungi utilize that entry point and colonize the wood causing wood decay. This creates hazardous situations. As we've seen, it takes a lot of time, effort, and money to remove these diseased trees.”
Held’s work focuses on DNA verification of the various fungal strains collected from infested samples.
“My role has just been to look at the fungal diversity and, as a whole, to try to understand how the groups are related,” said Held. "We're doing a lot of different DNA sequencing and looking at a region of DNA that basically serves as a 'barcode' for individual fungal species.”
“As we've seen, it takes a lot of time, effort and money to remove these diseased trees.”
Working alongside Held is Nick Rajtar, a master’s candidate in plant pathology, who explained the broad mapping approach the team is taking.
“We’ve been collecting infested ash samples not only locally, but also from Wisconsin as places there tend to have more established EAB infestations than in Minnesota. We hope to use these samples to find where their fungal communities match and differ from fungi here,” said Rajtar.
Already, they have isolated nearly 1,200 varieties of fungi, including many new species and nearly 200 strains that demonstrate either significant wood-decaying or insect-killing potential.
The research team identifies fungal specimens collected from EAB-infested ash trees by growing them in culture plates. (Credit: Caro Silvola, MITPPC).
Community partnership in action
The team’s work is highly dependent on its ability to receive samples of infested ash trees from local park boards and government agencies.
“If we didn't have these counterparts in the city and state levels, we just couldn't do our research,” said Held. “Without these types of relationships, we couldn't get those infested trees. It’s a critical part of the whole project.”
Luckily for the research team, the Minneapolis Park & Recreation Board was happy to provide samples. Phillip Potyondy, the Board’s Sustainable Forestry Coordinator, assists in overseeing the collaboration.
“As custodians of Minneapolis’ urban forest, we're always interested in partnering on research projects. What we learn helps us make better decisions and make these natural spaces a better place,” said Potyondy.
“As custodians of Minneapolis' urban forest, we're always interested in partnering on research projects. What we learn helps us make better decisions on how to make these natural spaces a better place.”
This project has captured the interest of forest and land managers across the state, particularly when it comes to mitigating the hazards of tree removal in the wake of EAB.
Plant pathology Ph.D. candidate Sofia Simeto Ferrari sprays ash logs with fungal spores to see if they can help control emerald ash borer. (Credit: Caro Silvola, MITPPC)
“I think about [the effect of wood decay-causing fungi] from the practitioner standpoint – about arborists and property owners and how we make safe decisions in the field while working with infested trees,” said Potyondy. “Right now property owners and municipalities are treating a lot of trees with insecticides to control EAB. But insecticide is not fungicide. You may kill the insects up to a certain threshold, but the damage done to the wood by decay-causing fungi could still continue, putting arborists and property owners at risk."
The Minneapolis Park & Recreation Board provides large sections of EAB-infested trees to Blanchette and Bushley. Likewise, the Wisconsin DNR has also provided samples.
Some of the fungi associated with EAB may even be damaging to trees on their own as disease agents. The only way to know for certain is to test suspected fungal pathogens on healthy trees and track disease symptoms. Testing these fungi on large, healthy ash trees is difficult and may kill trees unnecessarily. Testing with younger ash saplings is more efficient. Collecting un-infected ash saplings for testing, however, proved to be difficult given EAB's rise in recent years. Growers are reluctant to raise a tree species that face such a high risk of infestation.
“It’s immensely hard to find ash trees in a nursery setting, as people often don't grow them anymore,” said Rajtar. “Luckily, J. Frank Schmidt & Son Co. Wholesale Tree Growers in Oregon were willing to donate 120 trees for our studies.”
Post-doctoral researcher David Showalter holds a culture dish containing individual emerald ash borer eggs on pieces of paper and a cotton wick for hydration. The eggs are used to inoculate ash tree samples and screen fungi for biocontrol properties. (Credit: Caro Silvola, MITPPC)
Top: Fungal fruiting body specimens collected by professor Robert Blanchette for use in his forest mycology laboratory classroom. Bottom: Showalter explains how logs that have been sprayed with fungal spores are inoculated with emerald ash borer eggs. He secures the insect eggs on the tree with gauze and waits for the larvae to begin feeding and interacting with the fungus. (Credit: Caro Silvola, MITPPC).
A little help from our (fungi) friends
While the research team and its external partners are collectively thrilled about the potential impact this research will have for arborist safety, they are also looking forward to the possibility of identifying certain entomopathogenic fungi – fungal species that cause disease in insects – for biocontrol of EAB. Assistant professor of plant and microbial biology Kathryn Bushley, graduate student Sofia Simeto Ferrari and post-doctoral researcher David Showalter are working on this aspect of the project.
“Biocontrol would be one more piece in the puzzle of how to slow the spread of emerald ash borer.”
“Biocontrol would be one more piece in the puzzle of how to slow the spread of EAB,” said Potyondy. “Especially on the edges of EAB’s climate range, a fungal disease that infects EAB could take the lead in moving it from a primary pest to a secondary pest, particularly when there are other control agents working in harmony with it.”
Currently, EAB infestation has been limited primarily to the central part of the state and the Duluth area. By analyzing this potential control method arborists will have another tool to add to their management strategies as they work to slow the spread of EAB and protect Minnesota forests. Potyondy finds that prospect exciting.
“This is a huge piece of knowledge to help avoid calamities at multiple scales. So it could have a very big impact in either changing management or cultural practice out in the field and can lead, I think, to a better urban forest.”
Funding for this project was provided by the Environment and Natural Resources Trust Fund as recommended by the Legislative and Citizen Commission on Minnesota Resources.
About the Author
Caro Silvola is a Communications Intern with the Minnesota Invasive Terrestrial Plants and Pests Center (MITPPC). She is a double major in Bioproducts & Biosystems Engineering and English Literature and is highlighting research-community partnerships in the summer of 2019. Outside of the office, Caroline likes biking, making art, exploring, volunteering in her community and participating in environmental movement spaces.