EAB Biocontrol

Emerald ash borer (EAB) has become widespread in Minnesota and is a major threat to our state's ash trees. Efforts to limit EAB populations using biocontrol in Minnesota are underway. Learn about these efforts with Minnesota Department of Agriculture’s EAB experts, Jonathan Osthus and Chris Mallet, on this episode of Smarty Plants. 

Smarty Plants is a podcast of the Minnesota Department of Agriculture. Visit www.mda.state.mn.us/plants-insects/smarty-plants for more episodes. Look for a new episode of Smarty Plants every month.

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Jennifer Burington: 0:19

Welcome to Smarty Plants, a Minnesota Department of Agriculture Podcast, informing the public about invasive species that affect our environment and agricultural resources. My name is Jennifer Burington, and I will be your host, Emerald Ash Borer or EAB as it's also known as an invasive insect that feeds on ash trees. EAB was first discovered in Minnesota in 2009. Since then, EAB has become widespread in most of Minnesota. Which has greatly affected our ash trees. The Minnesota Department of Agriculture in Partnership with the United States Department of Agriculture is using BIOCONTROL to combat EAB. Jonathan Osthus and Chris Mallet from the Minnesota Department of Agriculture are joining us today to discuss the basics of Biocontrol and how it is being used against EAB. Jonathan is the Emerald Ash Borer Technical Assistance Coordinator for the Minnesota Department of Agriculture's Plant Protection Division. He began working on early detection and management of Emerald Ash Borer shortly after it was first found in St. Paul in 2009. Chris is the Emerald Ash Borer Biocontrol coordinator for the MDAs Plant Protection Division. Chris started working on early detection of Emerald Ash Borer in 2012 and biological control efforts shortly after. Thanks for joining us, Chris and John.

Jonathan Osthus: 1:35

Thanks for having us. Thanks.

Jennifer Burington: 1:37

All right, so to get a little bit of background on Emerald Ash Borer, let's do a brief introduction on what it is and why it's important to manage this invasive pest in Minnesota.

Jonathan Osthus: 1:48

Well, that's a great question. Um, Emerald Ash Borer is a, a non-native insect that arrived in North America sometime in the early to mid nineties, and it showed up in Detroit, Michigan area. Uh, likely brought into the ports there through solid wood packaging material. And then, uh, fast forward, uh, several years later, it showed up in St. Paul, Minnesota in 2009, and it has been spreading ever since. Um, uh, north American ash trees don't have, uh, natural resistance to this insect 'cause they didn't co-evolve with it. And so there aren't these natural enemies or these, this natural resistance that helps keep the pest in check. And so it causes widespread ash mortality. And so now what we have in, in North America is a very big problem, uh, where we're losing lots of trees, um, rather quickly. And it's now found in, uh, 38 states and five Canadian provinces. So it's spread out throughout much of North America and the native range of, of ash.

Jennifer Burington: 2:46

So that's a lot. I know we have about almost a billion ash trees in Minnesota, and that's a lot over a large area too, so. What is Biocontrol and how does it differ from some other tools used to manage these pest as, and we've talked about other times on other podcasts about, um, cold and having, um, insecticide use or things like that to help protect trees. Like how does this differ from those? If you wanna help out Chris.

Chris Mallet: 3:15

Yeah. So biological control is the intentional introduction of natural enemies from one geographic area to another to manage an invasive pest that happens to be there. It is a long-term strategy aiming for permanent pest suppression. By establishing a natural balance between the pest and its natural enemies, it's not going to eradicate the pest, which some chemical treatments aim to do on a smaller scale. Uh, the method of biocontrol is typically used at the landscape level where other management methods, such as chemical control or physical removal is not feasible or possible.

Jennifer Burington: 3:47

Thanks. Yeah. We have a, like you said, about a billion ash trees in the state. That's a nice option for large ash forests, um, that we have in different areas.

Jonathan Osthus: 3:57

Yeah, it could really play a crucial role in some of our black ash forests in the more northern part of the state, so north central and northeastern Minnesota, where we have these large swaths of basically a monoculture of black ash. Um, it's the, the main tree species that makes, uh, the, the dominant trees in those forested wetland areas.

Jennifer Burington: 4:16

So going along with that, how, how is Biocontrol, um, being used to manage EAB specifically?

Jonathan Osthus: 4:25

So Biocontrol is being released in these natural areas where other management tools, like Chris mentioned, uh, like doing sanitation where you are removing known one infested trees or treating trees with, uh, in like insecticides that help control, um, it within an individual tree, that's just not feasible at a, at a forced landscape level. There's far too many trees to, to be dealt with. And, you know, getting equipment into, uh, remote areas is also a very tough thing to do and can be very cost prohibitive. So, uh, by releasing these, these parasitoid wasps, um, in these forested settings, we're hoping to get them established with Emerald Ash Borer population so they can spread with it as it moves into new areas and suppress that Emerald Ash Borer population trying to reduce overall tree mortality.

Jennifer Burington: 5:13

Yeah, we definitely like to enjoy our shade on these hot, sunny days and enjoy, uh, being outdoors with that. So, um, how. So Emerald Ash Borer attacks ash trees and it, um, is underneath the bark, um, as a larval stage and stuff. And so how do these insects work to limit the EAB population?

Chris Mallet: 5:37

So, EAB Biocontrol is hoping to manage EAB at the landscape level, not the individual tree level. So MDA is currently releasing three parasitoid wasps into the environment that use Emerald Ash Borer to complete their life cycle. They can't exist in the environment without EAB. Uh, there's two larva parasitoids. One of them is Tetrastichus planipennisi, and the other is Spathius galinae. Uh, these wasps target EAB under the bark and use their ovipositor, not stinger to lay eggs beside or inside the EAB larva. There's also an egg parasitoid called Oobius agrili that searches for EAB eggs on the outer bark of an ash tree and will insert its egg into an EAB egg. Uh, these wasps can also move along the invasion front with EAB. So more information on the three parasitoids. Uh,  Tetrastichus planipennisi, is about the size of a net and it has a small ovipositor, and it's very good at attacking EAB and branches and small diameter ash trees. But eventually, as ash trees grow, the bark becomes too thick, where  Tetrastichus cannot reach that EAB larva in the thicker bark. Fortunately  Spathius galinae, it's about the size of a large mosquito, has a far longer ovipositor and it can reach emerald ash borer in the thicker bark of far more mature ash trees. And then  Oobius agrili being that it attacks EAB eggs can attack EAB before it even starts feeding on the ash tree.

Jennifer Burington: 7:01

Thanks Chris. Yeah, it's interesting that there's multiple species that we have that are helping out to, um, manage EAB on a landscape level and. So how are, how do you guys pick which areas to release these EAB Biocontrol agents and like. What all goes into your planning?

Jonathan Osthus: 7:23

Well, first and foremost, Emerald Ash Borer has to be present at the site. You can't pre-release these, these parasitoids in, in areas, um, since they rely on Emerald Ash Borer to complete their lifecycle, that it has to be present. So that's number one. Uh, then we look for kind of these large forested areas. That's, you know, at, at a minimum of 40 acres, um, with at least a 25% ash component to that forest. Um, so that there's enough of a, of a source there for to help get those, those biocontrol agents established. Um. And we also need to have sites that aren't gonna have competing management. Um, done. So we need to make ensure long-term site access for doing recovery work. Uh, and that, you know, stuff isn't gonna be removed from there before the, those wass have a chance to do their job and get established with the Emerald Ash Borer population, uh, we like to find spots particularly on public land and connected to other woodlots that, uh, provide a good area for the, the Parasitoids to continue to spread with the EAB population.

Jennifer Burington: 8:25

So going along with that, um, what is considered a successful area or location and how do we know that it's been successful for EAB biocontrol and the continuation of these, uh, wasps that we have.

Chris Mallet: 8:41

So, MDA follows the U-S-D-A-E-A-B Parasitoid Ring Facility Guidelines, which also supplies all the parasitoids to MDA. Uh, they ship parasitoids in the summer, usually starting just after memorial day and releases take place, usually biweekly from Memorial Day until early September. Uh, we release Parasitoids for two consecutive summers, which should be enough to allow establishment in the release site. And then two summers after that last release, we'll go back and try and do recovery work to find that these parasitoids are still in the environment consuming EAB. Generations removed from what we released.

Jonathan Osthus: 9:22

Yeah. And to pile on with what Chris was saying, um, there's, there's a few different, since this is such a long-term strategy there, there's different kind of goalposts that we're, we're looking for to see if it's being successful so that you know, after your releases, you're looking for establishments, you know, at least a year after those final releases occurred. Uh, next you wanna show increasing levels of parasitism. So to show that those, those biocontrol populations are, are building up and actually starting to suppress that Emerald Ash Borer population some, uh, year over year. And then lastly, you want to, you know, eventually see young ash trees survive and grow and eventually be able to put out seed for, you know, natural regeneration in the forested system. So that's, that's the ultimate goal there.

Jennifer Burington: 10:04

Nice. That would be really helpful for especially those black ash swamps that are up north that are vast and large. Um, so. What, like you've talked about having the releases come from USDA and um, choosing where to release them. So how long have has the MDA been using BIOCONTROL for EAB and how many locations?

Jonathan Osthus: 10:29

So, uh, EAB Biocontrol, uh, and Minnesota was first initiated in 2010. And the initial release site, uh, was selected in Houston County, Minnesota. So on the far southeastern tip of the state, um, along the Mississippi River, that's where the first releases occurred. And then, um, the following year in 2011, we started doing releases along the Mississippi River in the Twin Cities metro area. And now you fast forward to 2025 and we've. Released at over 56 sites in 19 counties. And so a lot of that's in, you know, the greater Twin Cities metro area, the southeastern part of the state. But we also have releases in Stearns County, Cass County, and St. Louis County. So we've, we've covered a pretty big range. We do have a goal of trying to release these parasitoids in, um, all counties where Emerald Ash Borer has been found. And so, uh, when we put in for new release sites each year. Uh, we're looking for locations in counties that haven't received releases before.

Chris Mallet: 11:28

Yep. To date, we've released just over 690,000 parasitoids and release sites. Consist of city, state and county parks, state scenic and natural areas, nature centers, national wildlife, refuges in some tribal lands.

Jennifer Burington: 11:42

Yeah. It's a lot of counties to cover and there's more always being found so. With how many, um, what results are you seeing at these sites over the years? If you wanna pick a couple to talk about, I know you talked about the first ones down in Houston County. I remember going out on the island there to find them. Um, what are other, uh, places are you, uh, seeing and what results have you found?

Chris Mallet: 12:09

So we're still early on in this long-term project, but we are seeing establishment throughout the state from the southeast to the metro to the Duluth area pretty much everywhere we've released Parasitoids, where the release sites still exist in some forested fashion, we can find them, which means they're surviving our cold winters. They're continuing to attack EAB, even as populations naturally decline with the loss of the ash resource. But we're still waiting to see what impact they have long term on EAB.

Jennifer Burington: 12:38

So that's a lot of wasps out in the environment, uh, that are going after Emerald Ash Borer. So what questions does the public have most often about these? Because if they're out in the forested environments, these landscape forests, they're probably not gonna be coming into contact with them too much. But what do people ask most often about Biocontrol and how do you address that?

Jonathan Osthus: 13:01

Well, I'd say the first thing when people. Hear the word wasp, they tend to get a little nervous. Um, just 'cause they're used to, you know, the, the larger wasp that might, uh, sting them, you know, around their house, things like that. These are the size of gnats, they're really small. Um, you're not gonna come into contact with them out in the forest and they're not gonna sting you at all. So they're, they're non stinging. Um. And next would be, um, are they gonna cause damage to something else besides, you know, emerald ash borer? Because there's this, you know, history of biocontrol and kind of, uh. You know that it, you know, it escapes what is originally intended to be used for and then starts causing damage to something else. And so there's a whole lot of work that goes into determining if, uh, a species is host specific enough to be released as a bio control agent. And these wasps are very highly host specific and need Emerald Ash Borer to complete its lifecycle. They're not gonna establish without Emerald Ash Borer. So, um, that is not a worry in this, in this case.

Jennifer Burington: 14:02

So, yeah, walking around in these forests, I'm probably not gonna run across 'em. And if I do, I'm thinking that it's gonna be a mosquito anyway. And they're not yellow colored, so we won't be seeing those. So what is your hope for the future of EAB bio control and maybe just specifically about Minnesota?

Chris Mallet: 14:21

So on the timeline of EAB Biocontrol, we're still really early, even though we've been doing this for almost 15 years. Uh, we hope to continue releasing these wasps in Minnesota and finding a release site in each newly infested county. We hope research can continue to see what impact these wasps are having on EAB in the future. As EAB continues to spread throughout the state, and hopefully decades from now, they're still ash growing in the environment and still making up that 20, 30, 40% of some of our forests.

Jennifer Burington: 14:49

So does this mean that it's. Going to possibly be a time in the future that Emerald Ash Borer won't be in the landscape or in an ash tree,

Jonathan Osthus: 14:59

unfortunately, no. Um, so Emerald Ash Borer is gonna continue to be presented, present, um, for. The long term, our hope is that these was populations can help keep Emerald Ash Borer populations in check that allowed, uh, ash trees to survive. And so, um, not have widespread mortality and, you know, able to regenerate naturally in the forested system, uh, and play a crucial role, uh, ecological and cultural role in our ecosystem. Um, that's, that's the hope for the future and we'll, we'll see if it can do the job.

Jennifer Burington: 15:31

Thanks. Yeah. Hopefully, hopefully they can do their job and keep, keep growing along with EAB and spreading, um, as it as Emerald Ash Borer spreads into more counties. So finally, uh, if you guys do have, uh, can you give us some steps everyone can take to help control the spread of emerald ash Borer.

Chris Mallet: 15:51

Uh, don't move firewood like every other forest pests and also report trees. You suspect to have EAB in new parts of this state to the MDA.

Jennifer Burington: 16:00

Yeah, and you can report that to report Aest, which we have, uh, on our website. You can visit www dot mda dot staten us slash report, aest all one word, and you can, um, use our online tool that you can upload pictures onto our online form. You can send us an email or you can give us a call. We do have our phone number listed on there as well. So if you happen to be out and about and you see a ash tree that's looking uh, unhealthy, you can take a picture of it and send it into us and we'll have John and Chris take a look at it. So, Jonathan, why is it important to have ash, especially in these like black ash swamps up in the landscape that you were talking about in Northern Minnesota?

Jonathan Osthus: 16:47

So, uh, black ash is a. A culturally significant species that plays a very important ecological role and cultural role. So, uh, indigenous cultures, they make things like, uh, they do basket weaving and things like that and use, use black ash. And then these black ash forests, uh, they're, it, they're the, the keystone species. So there's not much else that will grow there. And so the worry is if Emerald Ash Borer kills all these black ash trees and this, these large swaths of, of monoculture, um. We won't have trees growing there in the future. And then that gets swamped out, and then you have a wetland and all the other, you know, flora and fauna that depended on those, uh, ecosystems, uh, won't have that niche any longer. So it can have some cascading impacts, uh, for, for our environment.

Jennifer Burington: 17:37

So where can people find more information, Chris, to learn about what EAB BIOCONTROL is.

Chris Mallet: 17:43

The MDA has an Emerald Ash Borer biocontrol website, which includes information on the PARASITOIDS and release numbers. It also has a map specifically for EAB biocontrol, which shows past and present release sites, as well as recovery locations.

Jennifer Burington: 17:57

So when you go out to these recovery locations and. Um, try to figure out if the wasp are actually doing their job and they're actually still living there. Like you're saying, you go back a year or two later. How, how do you find them and how do you survey for them to know that they're, they're actually there. You're talking about these teeny tiny little things that go after eggs and gnat size and stuff like that. So how, what do you do?

Jonathan Osthus: 18:26

Well, we have a few different ways that we, um. Try to see if they've established at a site. So one involves, um, the. Sampling whole trees and peeling the bark off to look for Emerald Ash Borer tunneling and to look for the, the wasp larvae within those Emerald Ash Borer galleries. Um, another way is where we scrape off some outer bark and then let it dry out and then run it through a sieve. And then look for emerald ash borer eggs that have been parasitized. 'cause they turn black in color after they've been parasitized, uh, underneath the microscope. And so those are about a millimeter big when you find them. Uh, so it, it can be kind of tedious work, but uh, when you do find something, it's quite exciting. Uh, and, and in the summertime we will put out, uh, yellow pan traps. Um, they're attracted to color yellow. And then, uh, we will, you know, collect samples every week or every other week throughout the summer. And, and then look for the larval or egg parasitoids in those, those pan traps. And, uh, lastly there is, uh, sentinel logs that can be placed out. So there's these, um, purposely infested little, what we call ash bolts, that we hang on trees in, uh, release areas and then set them out for a month. Um, 'cause they have these, uh, mature, you know, late instar larvae, emerald Ash Borer larvae underneath the bark in these little ash bolts. And then after we leave 'em out in the field for a month, we bring 'em back and put in a, a rearing chamber and see what emerges and see if we have any parasitoids in there.

Jennifer Burington: 19:56

Thank you John and Chris for the interesting information on EAB and ongoing biocontrol efforts here in Minnesota. It was great to learn about this program and the steps being taken to manage EAB populations. This has been Smarty Plants, a podcast from the Minnesota Department of Agriculture. Our producer is Brittany Raveill. Our editor is Larry Schumacher, and I have been your host. You can learn more about pests and other invasive species that affect our environment@www.md a.state.mn us. And while you head to our website, we'll be working on the next episode of Smarty Plants. See you there.