Scientists testing fungi to protect Minnesota's one billion ash trees

NINA MOINI: A shiny green beetle has transformed city streets and forests in parts of the United States. You may have heard of the emerald ash borer. It's been found in 59 counties of Minnesota. And it has especially affected the southeast corner of the state.

The beetle depends on ash trees to survive and reproduce. It lays eggs into their bark. Then those eggs hatch into larvae that feed on the living tissue of the trees, eventually killing them. And then they become beetles and fly off to the other trees.

So scientists at the University of Minnesota have found fungi that can interrupt this cycle by killing the beetles. Joining me to explain is Colin Peters. He's a PhD candidate and lead author of a recent study about using these fungi to protect ash trees. Thanks so much for being on the program, Colin.

COLIN PETERS: Hey, thank you for having me.

NINA MOINI: So I understand researchers in your lab found there are fungi in Minnesota that kill emerald ash borer. So, what did you find out with your research? And do say fungi or fungi? I have to know.

[LAUGHTER]

COLIN PETERS: Either is acceptable in the world of mycology. However, I say fungi.

NINA MOINI: OK, I will too.

COLIN PETERS: The kind of soft J.

NINA MOINI: All right. Soft J. Got it. So what stood out to you with this research?

COLIN PETERS: So, this research was exciting because this is the first step toward the development of a biological control for emerald ash borer using these insect-killing fungi. And what was cool about this study is that the majority of fungi that we tested originated from Minnesota. And so what we found is that we have fungi here in the state that are able to kill these beetles.

NINA MOINI: And let's back up and just talk about why this is so important to try to find a solution and protect these ash trees.

COLIN PETERS: Well, ash trees comprise a major component of our forests in Minnesota. Our state is unique in that we actually have the largest population of black ash trees in the United States. And the majority of those black ash are in our northern marshlands. So wet forest types, where they can form these really expansive stands where almost every tree is a black ash.

NINA MOINI: Wow.

COLIN PETERS: And also, they are a major component of our urban forests. So in some municipalities, ash trees were largely planted to replace elms after Dutch elm disease swept through. And so they can comprise up to 20% of the urban forest canopy.

And so these are a super important tree species in our state especially. And there just aren't that many options for land managers to control for emerald ash borer in these natural forest settings. And so we need to be developing more options for land managers, more tools for their tool belt.

NINA MOINI: And there are areas along the river in the Twin Cities where you can see many dead trees that were infected, to your point about the canopy. Why has this beetle had such a dramatic impact?

COLIN PETERS: Well, so this beetle was introduced. It is native to eastern Asia and made its way over to North America, we think, in the 1990s on infested wooden shipping materials. And the problem is that in its native range in Asia, it's mostly attacking stressed ash trees.

And these Asian species of ash trees have some resistance to the beetle's feeding, whereas here in North America, our ash species, by and large, have no resistance or drastically less resistance to the beetle's feeding. And so once it arrived, it just caused devastation to our ash trees. And now it's actually threatening essentially the extinction of a whole genus of tree across the continent. So this is a big deal.

NINA MOINI: Yeah. I mean, when you said the '90s, that doesn't seem like that long ago to me. I mean, it is at this point. But I wonder if you find these types of invasive species and things getting worse over this 30-year time frame as maybe the global economy relies more on each other.

COLIN PETERS: Well, certainly it has gotten worse just in that the sheer number of ash trees that have died exponentially increases as the range of the beetle increases, so--

NINA MOINI: Yeah. I wonder too, the state and federal agencies I'm reading here have released three types of parasitic wasps that specifically attack emerald ash borer. So, can you explain what the difference is or if it's better to use the fungi?

COLIN PETERS: So I wouldn't say that it's necessarily better to use the fungi. I think our goal with our research really is to create additional tools. And actually, ideally, our fungi could be used with those parasitoid wasps.

And we have yet to look at the interactions between our fungi and those wasps, for example. But the potential for that could mean more effective control of the beetles in these natural forests.

And so the wasps are generally targeting one life stage of emerald ash borer, depending on which wasp species we're talking about. And what's cool about those wasps is that they are reproducing out in our forests and have been naturalizing and establishing themselves.

NINA MOINI: Nice.

COLIN PETERS: And so they provide a baseline level of EAB control after their release.

NINA MOINI: And EAB control is?

COLIN PETERS: Emerald Ash Borer population control.

NINA MOINI: Got it. Got it. So I do wonder too, Colin, since the fungi don't exclusively attack emerald ash borer, do you have ways to ensure that it doesn't kill maybe other insects or have an unintended consequence on the ecosystem?

COLIN PETERS: Yeah, this is a great question. So, these fungi that we found were successful at killing emerald ash borer. They are considered generalist insect pathogens. So they have relatively a broad host range of insects that they can infect.

A part of our job as researchers is to try to minimize the potential for that nontarget effect. And so we're doing that firstly by using native fungi, which already are on the landscape in Minnesota.

And then we are working to develop targeted approaches at delivering those fungi to emerald ash borer specifically. So, essentially, in a nutshell, the fungi themselves can kill a broad range of insects. But the way that we are delivering the fungus, we are working to make that more specific toward emerald ash borer.

NINA MOINI: Would you say that's the next steps then in your research that you're talking? I'm just wondering what's next. Like, when might people really begin to use this?

COLIN PETERS: Well, we are currently testing out these fungi in field trials. And we're trying out a couple of different methods for applying them to the land. And so one is using these autodissemination devices, which are traps that coat the beetles in spores.

And then we are also trying injecting trees, ash trees, with these fungi. So this research is still underway. And again, this is essentially a first step toward that ultimate goal. But within the next couple of years, we can expect to see some more information about this project surfacing.

NINA MOINI: It's really great to talk about possible solutions on the show. And it's really great to hear how that research is going. So we really appreciate your time. I learned a lot. Thanks, Colin.

COLIN PETERS: Thank you.

NINA MOINI: Colin Peters is a PhD candidate in the University of Minnesota's Department of Plant Pathology and the lead author of a recent peer-reviewed study published in the journal Forests.