Mar 06, 2023 —
When the emerald ash borer was first discovered in Akwesasne Mohawk territory in 2016, it was a painful blow. Not only are ash trees essential parts of the forest, but they’re also the raw material for the basket-making tradition that’s at the heart of Mohawk culture.
So when scientists in Akwesasne took on how to stop the beetles from devouring all the ash trees, they started by observing how the insects kill a tree.
“They carve these very characteristic feeding galleries, which are like tunnels,” said Jessica Raspitha, land resources program manager for the St. Regis Mohawk Tribe’s environment division. “Over time, that damage gets so excessive that it cuts off the vascular tissue, which prevents it from transporting the water nutrients through the tree, effectively killing it.”
The Tribe recently got the third year of a nearly $650,000 U.S. Department of Agriculture grant to find innovative ways to keep the emerald ash borer population in check, mostly without using toxic pesticides.
Raspitha told David Sommerstein about a series of measures rooted in biology and silviculture designed to outsmart the EAB and keep the insects from destroying all the ash trees in Akwesasne. She started by describing one way, setting up what she calls “trap trees.” Their conversation has been lightly edited for clarity.
JESSICA RASPITHA: What that entailed was removing sections of the bark on the trunk, and that induces stress in the tree. The tree releases a certain type of pheromone that attracts the EAB, and at the end of the season, that tree would then be removed from the forest. We would strip the bark off of it to see how many EAB have come into that tree.
So this serves both as a population sink because the EAB was drawn to that particular tree rather than toward the healthy trees and it also allows us to evaluate the population.
DAVID SOMMERSTEIN: Wow. So you were actually attracting the emerald ash borer, like ‘hey, come over to this tree. So we can kind of get a sense of what’s going on, but also so that you won’t go over to all those other trees.’
RASPITHA: Yes, that was the intent and how it works. What we did find was that the populations were growing, but we didn’t find any old galleries. All the galleries that were there were new, which indicated that our detection methods were fairly early and that we were seeing an early infestation and not one that had been building for years.
SOMMERSTEIN: How widespread is the emerald ash borer in Akwesasne in the territory? What percent of ash trees are infected? Do we know that?
RASPITHA: I don’t know that we know a specific percentage. We do know that since its first finding in 2016 in one of our green funnel traps, we’ve continued the funnel trap method every year since and we’ve seen it slowly spread from one corner of the reservation all the way through the territory. So we do know that it is everywhere. But the exact percentage of infestation is unknown.
So to speak to some of the other approaches we’ve used, some of them are a little more long-term than the population sinks. The population sinks are good for trying to prevent further spread in certain areas. But we also do silviculture work. So that’s part of a long-term strategy.
In some of the state forests around Akwesasne, we have traditional rights within certain state forests. So those are customary use areas that we also try to protect as well as the trees within the tribal territory. Silviculture is a form of forest management. It includes the removal of some trees in order to prompt desired growth.
We are also doing some pesticide application. So we have been for the last three years now doing trunk injections on certain high-value ash trees. We’re using an insecticide made out of emamectin benzoate. It’s injected into the trunk of a tree, and what happens is that when the eggs of the EAB hatch, the larvae are not able to eat the vascular tissue because it will kill…
SOMMERSTEIN: Yeah, I’ve heard about that, that you can protect certain trees and inoculate them. How do you decide what’s a ‘high-value’ ash tree?
RASPITHA: That’s done both under the guidance of our tribal forester and also we have the great fortune of working with a sixth-generation basketmaker on our team. Our land resources technician has a really good eye for spotting what is a high-value tree in terms of basketry. They have a good eye at evaluating what is the high-value tree in terms of forest health.
But the limiting factor with the pesticide injection is that, for one, the insecticide itself is expensive. And for two, there’s a lot of time that’s required to evaluate whether a tree is a good candidate for injection or nor. But to date, we’ve injected 118 trees, so we’re able to do about 50 a year.
The other drawback to it is that the insecticide only works for about three years. So we do need to revisit the site every couple of years to make sure that they’re still healthy.
SOMMERSTEIN: So what does this all mean for the future of ash trees in Akwesasne? I mean, this is a problem across the North Country, certainly in the Adirondacks where there are huge amounts of ash trees, but in Akwesasne, it’s an especially difficult problem because not only are they beautiful trees that are a huge part of the ecosystem, but they’re also a huge part of the culture and people’s livelihoods in making black ash baskets and basketry.
RASPITHA: So right now the trees are still in a steady decline. But one of the other long-term methods that we are starting to work with is facilitating the release of bio-control parasitoid wasps. So we are working with three different species. Two of them attack the EAB during the larval stage. One attacks the egg stage.
SOMMERSTEIN: Wow, certain kinds of wasps that attack the emerald ash borer?
RASPITHA: Yeah, so we’ve been working really closely with USDA to try to evaluate the sites, because you need to first find a thriving EAB population, so the wasp has something to eat. And once we’ve established that there is a sufficient population of EAB, we release the wasps, and then we revisit those sites every year to make sure that both the EAB populations are declining and that the wasp populations are sustaining.
I think the long-term goal, at least from my perspective, is that we will eventually reach a point where if our biocontrols are sustaining their populations, they will be able to keep the EAB populations in check. And so not so much that we’re reaching toward eradication of the EAB but that their populations won’t reach the point where they are killing our trees.
SOMMERSTEIN: Do you feel pressure because you’re in charge of this thing, you’re trying to maintain this huge Mohawk tradition?
RASPITHA: Some pressure, yes, because the ash tree is so important to the culture, and the cultural practice itself relies upon the availability of the resource. It’s something that’s been available to continue to practice for thousands of years, so there’s a lot of fear that if our control efforts don’t work, that it might not be there in the future, to sustain the actual cultural practices that go with it. But I also think it’s important to acknowledge that while our current efforts have only been going on for the last three years, the work to preserve ash trees has been going on for decades.