Bug fight: the emerald ash borer vs. parasitic wasps

Michelle Strong (co-host): You can't see it, but there's a fight happening in Canadian forests right now with millions of ash trees dead across North America and billions more at risk.

Greg Rogers (co-host): Today we're talking about the emerald ash borer, an invasive beetle, that's been doing some serious damage since it arrived here in 2002.

Michelle. But Canadian scientists are on it. They released 100,000 wasps into the wild to fight back.

Greg: The battle has already begun.

Announcer: Ladies and gentleman, in the left corner, presenting the reigning, the defending, the pest currently eating its way through ash trees across North America, the emerald ash borer!

Greg: Native to eastern Asia, these beetles are highly invasive. Their body of iridescent metallic green can grow to be 14 mm long, with tiny tooth-like edges on their wings. These woodland monsters lay eggs that hatch into creamy, white larvae twice the size of their adult form.

Announcer: And now, in the right corner, presenting the opposing, the challenging, the predatory, parasitic wasps!

Michelle: Native to Asia, these are tiny creatures, at less than 4 mm long (small but mighty). These bad boys feed on the larvae of the emerald ash borer. Completely ruthless in their survival, they even lay eggs inside their larvae, effectively killing them in their infancy.

Announcer: It's time. The battle of the ecosystem begins!

Greg: I'm Greg.

Michelle: And I'm Michelle.

Greg: And this is Inspect and Protect, the official podcast of the Canadian Food Inspection Agency.

Michelle: So today we're talking about biological control agents, which is basically the concept of introducing a new species to control an existing species. Basically, bugs fighting bugs.

Barb Ustina (Simply Science co-host): You mean bugs literally duking it out with other bugs? Did you hear that Joel?

Joel Houle (Simply Science co-host): Yeah Barb, it has a nice ring to it. Maybe we should do something like that too!

Michelle: Greg, is that who I think it is?

Greg: Barb and Joel? From Simply Science? What are you guys doing here?

Joel: Hey Greg and Michelle, don't mind us. We're just looking for story ideas for our Simply Science podcast. Like, you guys know, the podcast that talks about the amazing scientific work our experts at Natural Resources Canada (NRCan) are doing? Did I also mention our podcast is called Simply Science?

Michelle: Mhmmm.

Greg: Yeah, you mentioned that.

Barb: You know Joel, we have more than a few entomologist here at NRCan that are studying insects like the Spruce Budworm, and I wonder if there are bugs fighting that pest? We should look into that.

Joel: Oh, we definitely should! And you know what we should do… We should totally borrow the whole wrestling theme.

Michelle: What?

Barb: Uh-huh. Thanks for the ideas guys, but we really need to go. We have our work cut out for us now.

Greg: So, I guess this is now a collaboration with the Simply Science team at NRCan. More bugs for everyone I guess!

Michelle: If you don't already follow their podcast on SoundCloud, you definitely should. Now, let's dive back into the Canadian wilderness. We wanted to know more about the introduction of wasps into our forests, so we spoke with 1 of Canada's top experts.

Chris MacQuarrie (guest): My name is Chris McQuarrie. I'm a research scientist with Natural Resources Canada, Canadian Forest Service. I work in Sault Ste. Marie, Ontario. I'm an entomologist, forest entomologist. I like bugs.

Greg: So Chris, I can imagine when we're talking about introducing a swarm of wasps, that there could be concern for people. You know, those visions of, you know, stinging insects. But it's my understanding these particular wasps don't sting.

Chris: No, taxonomically, we have to call them wasps, because that's the larger group of insects that they belong to. And physiologically and evolutionarily, they're related to, like, yellow jackets and paper wasps and hornets and things that people know. Biologically, they don't behave the same way. The thing that we would call the stinger like on a paper wasp has been modified through evolution to lay eggs in the host or on the host insect that that they're interested in parasitizing. And these are all really, really tiny things. And they're only interested in laying eggs.

Greg: So where would we get all these wasps from? Like, is there a giant wasp farm somewhere?

Chris: So, when we're doing a biological control program, we'll set up a rearing facility to grow these agents. So in our emerald ash borer program, there are 2 rearing facilities. The largest 1 is in Michigan, run by the U.S. government, and they produce hundreds of thousands of these wasps every year for distribution across North America within the range of emerald ash borer. And we have a smaller facility at the Natural Resources Canada laboratory in Sault Ste. Marie that produces 2 of those agents. I mean, when Canada first got into forest biological control back in the '20s and '30s and the '40s, they set up a whole lab in Belleville [Ontario]. It was a purpose-built building that just it was just there to grow biological control agents. And it did that for 30 or 40 years. And it was a huge operation. So it's a big operation just to sort of grow insects.

Michelle: So why were these wasps the perfect opponents?

Chris: Because in the native range of emerald ash borer. So, in Asia, parts of China and Russia, these insects... Basically, they eat a lot of emerald ash borer. And they are 1 of the things that helps control those populations within its native range. These particular species are really only mostly interested in emerald ash borer. And because of that, then we hope that they will be good at helping control it here. But they also won't go off and eat something else that we're interested in, like another native North American insect. That we don't want to have negative impacts on. So it fits into that nice kind of sweet spot of doing that.

Greg: Do they have different fighting styles? I've got to know, you've got to tell me like, how do they actually kill the emerald ash borer? Like… the nitty gritty details.

Chris: Yeah, so in the emerald ash borer program, we released 3 species in Canada. 1 is called the Tetrastichus planipennisi. Another 1 is called Oobius agrili. And the third 1 is called Spathius galinae.

Michelle: Wow! Slow down. Can you repeat that? Can I even spell those?

Chris: So basically, we have we have 3 species that were released, and we call them Tet and Oobius and Spathius. So Tet and Spathius are what we call larval parasitoids. So the larva of emerald ash borer is the grub. It's the white stage underneath the bark of the tree. And that's what's actually killing the tree. I mean, that's what eats the phloem and strangles the tree and ultimately causes it to die. Tet and Spathius have the ability to find those larva underneath the bark and then they can insert their stinger... like through the bark of the tree and deposit an egg on or in or nearby an emerald ash borer larva. They will lay 1 egg or more than 1 egg. So they get they get a whole bunch of wasps coming off of 1 larva. And then those parasite insects develop. They go through their whole development inside or on top of a normal emerald ash borer larva and then they emerge. So you get a bunch of wasps, parasitoid wasps, coming out of the tree and you get a dead emerald ash borer. Oobius is different. Oobius comes along and it's a tiny, tiny, tiny wasp like, you know, the tip of a pin sized, like this is a tiny insect. And it comes along, finds an emerald ash borer egg and lays its egg inside the emerald ash borer egg and then its egg hatches and completes its entire development within an emerald ash borer egg and then emerges as a wasp.

Greg: That sounds so sci-fi.

Chris: What we say is, if you've ever seen the movie Alien, where the thing comes bursting out of the dude's chest. That's how parasitoids work. And these are..

Michelle: Thanks for bringing that up, I was trying to get rid of that image.

Greg: It's crazy. Like when we first found emerald ash borer in New Brunswick here, I had a dream that somebody had designed a drone that could like hone in, like a little miniature robot that could hone in on the metallic green color of the emerald ash borer and like, hunt it, kind of thing. So, I mean, maybe that'll happen someday, but I never...

Chris: Well, I mean, I mean, evolution has done that. That's a parasitic wasp, right? That can find the emerald ash borer.

Michelle: There you go.

Chris: The reason we use these techniques is ...especially with something like the emerald ash borer, is it's super hard to find. When you have a pest insect like that, the tools that you're able to use to manage it get really limited, because, if you compare it to like a crop pest, if it's a crop pest, then I'm a farmer. I can go out and I can survey for it.

Michelle: Right.

Chris: And then I can decide, OK, do I need to spray or not spray or do I need to go get some biological control agents or something like that? That doesn't work with something like emerald ash borer, that lives in a forest, that lives inside of a tree. Right. that's why biological control agents become sort of 1 of our tools of choice, because we're relying on work that evolution has done to be able to, you know, find the host insect and kill it to help us control that pest problem.

Michelle: So for the listeners, I mean, you're talking about how hard and how much time it can take to find emerald ash borer. How would people be able to identify emerald ash borer infestation on an ash tree?

Chris: With emerald ash borer, there's a progression of damage. So it looks basically like it doesn't have as many leaves as it should. Compared to, say, a tree, a neighbouring tree of a different species And then as the infestation progresses, you might start to see like woodpeckers. Woodpeckers are really good indication… As it goes on, you might start to see the exit holes, which look like the letter D, capital letter D.

Michelle: Right.

Greg: Okay, Chris, 2 questions. Why D-shaped exit holes? How is that even possible? How can they be in a D shape like…

Michelle: Yeah, I was wondering that, too.

Chris: So if you took an emerald ash borer beetle and looked at it head on, it would look like a D. When it needs to leave the tree, it has to chew a little hole from its gallery out through the bark. And so it's using its head. Pretend you're inside the tree and have to chew your way out. You're not going to chew like a hole any bigger than you would need to.

Greg: Okay.

Chris: So basically you would chew out a Michelle-sized hole or a Greg-sized hole and the hole in profile would look like you would profile.

Greg: Okay I'm satisfied with that answer. My other question is… my other question is, though, like woodpeckers? Why don't we just breed a bunch more woodpeckers if they like emerald ash borer so much?

Michelle: Right, I was thinking, yeah? Team up!

Chris: Yeah, totally, and again, you could and woodpeckers certainly control eat lots of emerald ash borer and they're an excellent of detecting, especially in the wintertime. Woodpeckers being birds. You know, it's hard to breed birds in general, I guess?

Michelle: They must eat other things, too.

Chris: Yeah, I'm not an ornithologist. And but as I understand, woodpeckers are also kind of like territorial. And so you can only… you couldn't release just flocks of woodpeckers because they would certainly disperse. And woodpeckers also being birds and being large vertebrates need other things. So like they need nesting cavities and holes and this kind of stuff. And when we talk about biological control, we talk about integrating it with other tactics. So a natural enemy like woodpeckers is 1 of those things that we want to enhance. We want to work with that. We don't want to replace it and we don't want to work against it. It's part of that whole pest control toolbox.

Michelle: So we have all these tools and tactics. How do we know that we're being successful? Like, what would success look like?

Chris: Success would look like ash trees on the landscape within their native range at some density. So emerald ash borer is here to stay. We're not going to eradicate it in North America. So the next stage is basically can we have an endemic population of emerald ash borer and still maintain ash on the landscape for its ecological and cultural uses? Right. So basically, we have 3 species we released, and we've released them across Southern Ontario, parts of Southern Quebec and New Brunswick. We've been doing this since 2012 and in the places where we've been able to go back and do our assessments, we found that all 3 species have established at places where we've released them. So all 3 species are established in Canada. And so that's what success looks like.

Announcer: And the winner is… the parasitic wasps!

Michelle: So, the release of emerald ash borer's natural predators is considered a successful operation, although scientists are still studying the situation.

Greg: But we had a few more questions… who gets to decide which insect predators are safe to let into Canada?

Michelle: To find out more, Greg and I decided to chat with Bruno Gallant, Senior Legislative Officer of the Invasive and Alien Species and Domestic Programs at the CFIA. So let's say we're looking into introducing a new predatory species. What's the process for that?

Bruno: The process really starts with what we call the petitioner. So the person who is looking to bring in that organism for biological control purposes. So we ask them to fill out a petition. And really, the onus is on that person to provide the information. So information such as why is this proposal being presented in the first place? What problem is there? We have requirements essentially to prevent what we call plant pests from coming into the country and being spread into the country. So plant-based, meaning things that could potentially be hazardous to natural resources, the environment, the economy, those kinds of things. And so the reason why they are being proposed for biological control is because the benefits of it, like controlling another pest, if you will. But the concern would be is that they do not have the risk characteristics as pests themselves, so that they're not coming into the country and doing a better job, if you will, than they are expected to do so, meaning that they are being brought into the country to control something, whether that be a weed or another insect. But we don't want that agent to start attacking other species that are not its normal targets or intended targets. So we want to make sure that it's not endangering our plant health resources.

Greg: So we're kind of like the gatekeeper. It's like a, like a kid who finds a wild animal or insect and wants to bring it home. CFIA is like the parent who makes the decision on whether it's safe or not.

Bruno: Exactly. And we really focus, the crux of our requirements with respect to agents is really the first releases of non-indigenous organisms. So things that are not here in Canada already being proposed for import from somewhere. So our requirements are really targeted towards those situations there.

Greg: Thanks Bruno, thanks Chris! I was super excited for this episode, it was awesome. We really appreciate you taking the time.

Bruno: And thanks for having me on the podcast today.

Greg: The wasps are 1 tool. But the fight's not over.

Michelle: Keep in mind, the spreading of emerald ash borer is mostly done by moving firewood. In some cases, it is actually against the law in Canada to move firewood from 1 region to another.

Greg: So be sure buy local, burn local. Ash trees are super important for Canada's landscape and aesthetic. If you think you've spotted the signs, report it to your local CFIA office, iNaturalist or EDDMaps. Or you can also find more information on our website.

Michelle: And don't forget to catch the other episode of this collaboration on the Simply Science channel. You can find the link to their episode in our description!

Greg: Yeah for sure, it was an absolute pleasure collaborating with Joel and Barb on this, so definitely check them out too!

Michelle: Don't forget to subscribe and listen to us on whatever platform you like.

Greg: We're on Spotify, Apple Podcasts, Google Podcasts, and probably whichever other app you use.

Michelle: This is Inspect and Protect, the CFIA's official podcast, all about food safety and plant and animal health.

[End of recording]