Spotted Lanternfly - Host Study
Dr. Gregory Setliff, associate professor of biology at Kutztown University, has been working with his students to conduct research to find out what plants Lycorma delicatula (spotted lanternfly) will feed on throughout the growing season.
- [Greg] Hi everyone, my name is Greg Setliff.
I'm a professor at Kutztown University.
And in early 2014, my team was brought in to examine what Lycorma delicatula, or the spotted lanternfly, was doing to native plants, and Pennsylvania trees in particular, in southeastern Pennsylvania in Berks County.
So just a quick review here.
Lycorma delicatula, or the spotted lanternfly, is known to invade other countries from its native ranges in Asia.
It has gotten into Korea and Japan.
And from studying those invasions, we know a couple of things, mostly from anecdotal observations and some scientific observations, that the preferred host of the pest is Ailanthus altissima, or the tree-of-heaven.
But it also attacks many other trees and plants.
In South Korea in particular, we know it goes after grape, which is a commodity of great concern in our area.
We know from looking at the literature that, although many of the plant species are not directly shared with Pennsylvania, many of related trees instead and other plants are.
So in case, we have about 60 species, where there's an overlap in the genera between Korea and North America in the plant list that the Koreans are seeing on being attacked by Lycorma delicatula and by what we have and expect to be possibly attacked here in North America.
So I'll go into, briefly, some of the experiments we've done in the 2015 and 2016 summers to examine this.
So we set out to try to find out what spotted lanternfly was doing here on PA plants and determine a couple of things about that, for example, if spotted lanternflies' host preference changed as they got older, which is something that we suspected from the literature.
We also wanted to identify possible alternative hosts that would support populations of spotted lanternfly while the main host of the Ailanthus altissima was being managed.
So our protocols were very similar to that of Pennsylvania Department of Agriculture's study on Ailanthus altissima.
So the PDA are using brown sticky bands on Ailanthus altissima, the primary host of the pest, to catch the migrating nymphs.
And the nymphs will climb up the tree from the base on a daily basis to get up to access the crown.
And so the sticky bands provide a barrier and actually capture and kill individuals.
We did a similar protocol on non-Ailanthus trees.
So these are your oaks and maples, and elms and birch, and lots and lots of other tree species, 30 more different tree species.
We did record, for example, a couple of things.
We made sure our trees were greater than 15 centimeters DBH.
They were larger trees.
They were within 10 meters from the edge of a path or the road.
That was not just for convenience sake, but also because we believed at the time that spotted lanternfly would not go deep into the forest.
That turned out not to be true.
But it was, we were taking a guess, and that was what we went with.
We did record the distance to the nearest tree-of-heaven from our non-tree-of-heaven trees.
And this was to measure the influence of close trees, of close primary hosts, on our non-host trees, what we thought might be non-host trees.
And then for our protocols, we took the bands down after they were out in the field for two weeks, every two weeks from May to September for two years.
For our research sites, we worked entirely inside the quarantine area at Berks County.
We worked at four different properties originally.
All of these sites were positive for spotted lanternfly in the very first season they were discovered, in the latent winter in 2014.
Now, we weren't a part of the project that time.
And so we were, in early May of 2015, starting our project.
There were no leaves on the trees.
There were no spotted lanternflies out.
So we had to choose sites where we knew they might be.
And so this is where we ended up working.
That turned out to be fortuitous because there's a lot of spotted lanternfly at these sites, even today.
We did work at a commercial orchard.
And that commercial orchard was using conventional management practices, like using pesticides.
And the pesticides did work to keep the lanternfly out.
So we did not continue to work there the following year in 2016.
We managed a total of, we examined a total of 30 tree species in our first two years in the study.
And here is a list of their scientific names And you may not recognize these, but there's a lot of things that are familiar to you, elm and sassafras, dogwoods, hickory, all kinds of things, birch and tulip tree, maples, oaks, so on so forth.
Essentially, a good cross section of Pennsylvania tree species.
All told, in the two years, we killed more than 12,000 immature spotted lanternflies.
You can see this band up here is spotted with spotted lanternflies They got stuck on this, the sticky band there.
Unfortunately, as all of the species in our study, just about all the species, tree species, non-Ailanthus trees and Ailanthus trees, had at least some spotted lanternflies on them over the course of the study.
And many of those had many hundreds of individuals attacking or using the tree in some way.
We weren't actually able to witness a whole lot of feeding, and so that's an encouraging thing.
We did see nymphs feeding on shoots and leaves, and on stems and vines, over the course of the study.
But we weren't able to document, or very easily document a lot of damage to those plants.
And that led to some changes in the 2016 study.
So, from our point of view, we have a total of 24 studies, 24 plant species.
Here are the common names that we did find being utilized by spotted lanternfly over the course of the study.
We did find that it didn't really matter if tree-of-heaven was close to these trees or not.
You know, a black walnut that had a tree-of-heaven next to it and a black walnut that was at least 60 meters away, or more than 60 meters away from, of a tree-of-heaven, had approximately the same load of spotted lanternflies on it.
So it did not seem to, at least our study indicated, it did not seem to have a strong influence.
But one of the things we were able to confirm statistically was that, overall, spotted lanternflies do prefer Ailanthus.
And this supports the Pennsylvania Department of Ag's decision to focus on this plant.
It gives a little support, sort of a, a focus management option.
And this is good because at least overall, while they are on lots and lots of different trees in the forest, they will preferentially align to Ailanthus.
Now, one of the interesting findings, at least interesting to me, is that while they're juveniles, what we call the first through the third instar stages, what is the time between their time they hatch from the eggs to their third molting stage, before they molt for the fourth time, at this stage, they are just as likely to be on other trees as they are Ailanthus altissima.
And so they are, there's no statistical difference shown here because they're just pretty much evenly distributed across a lot of the trees in the forest at this point.
When we looked at the development and the phenology of when the different life stages were on our trees, captured on our tree bands, we did not find a difference between that and what the PDA was finding on their bands, very similar phenology.
So not surprising that they're not developing any faster or slower on the others trees, and that's probably because, in reality, they probably move between them across the landscape.
But one of the findings that was significant in this study was that, at the end of July, right before August began, we began to see very few spotted lanternflies on non-Ailanthus trees, while the PDA continued to get spotted lanternflies for an additional 50 days on tree-of-heaven.
And so this is significant.
It suggests that, in the forest, the nymphs, at some point in their development, probably around the fourth instar, begin to leave other trees, and they congregate on tree-of-heaven.
And we, at some point, we eventually just stopped managing the non-Ailanthus trees because there was nothing happening on them, certainly when the adults were out.
So, we wanted to find out a little bit more about whether or not these non-Ailanthus trees could be used for, could be used as a secondary host.
We knew it wasn't the primary host.
That's Ailanthus altissima.
And that's where, at least at some point in their life, it appears spotted lanternflies have to congregate on in order to complete their life cycle.
And ideally, we were going to, early on in the season, capture nymphs and enclose them in these, what you can see here, are some sleeve enclosures, trap them on the branches of different tree species and keep them on there until they developed to adults or they all died.
Unfortunately, our funding and back-ordered sleeves sort of slowed that process down.
And by the time, and the fact that this, in 2016, we had nice, warm winter, and things seemed to be moving pretty quick, before we were ready to do the study, we already had adults in the field.
So we had to modify a little bit.
And we captured wild-caught adults, and trapped them into these sleeves.
And we ran replicates of black birch, sassafras, spicebush, sugar maple, tulip poplar, wild grape vine, and Ailanthus.
And then we also did a control, where we just took a dead stick and tied it up in the canopy and put a sleeve on that.
And what were doing is we were controlling to see if these guys, if these spotted lanternflies are able to live on black birch, which we know they are using as nymphs.
But as the adults, are they able to live on there?
Are they able to continue to survive over a period?
And they can survive better on black birch and sassafras than they can on just a dead stick?
And so that was where we started that study.
We ran this entire study two times.
So we had a total of 10 replicates each and each one having 10 adults.
So a hundred adults were subjected to this study for each species.
We standardized where the sleeves were in the canopy and how much sun and shade conditions they had.
So they were all at the same height in the plant, things like that, and every four days, we went back to check to see how many SLF, how many spotted lanternflies were still living.
We also indicated whether or not honeydew, which is the by-product from feeding on phloem, the waste product that the lanternflies produce when they're actively feeding.
We were seeing if there was honeydew produced on the sleeves and if any of the sooty mold that's associated with that was growing on the sleeves as well.
Now, this is a busy little graph here.
Essentially, what you have is the burgundy line, indicated here, is the control.
So this was essentially, spotted lanternflies trapped in a container with no living plant tissue.
And you can see, by eight days on, all the spotted lanternflies were dead in the study.
So percent of the population here, of a hundred percent alive to zero percent alive, by eight days, they were all dead.
Now, all of our plant species performed slightly better, but only slightly.
So all of our non-Ailanthus plants, with exception of Ailanthus and grape vine, these two lines here, they all did pretty well by day four but began to decline rapidly.
And by day eight, all but a few of them were dead.
By day 12, they were all dead.
So this is on black gum, sorry black birch, sassafras, the spicebush, and the maple.
So all of these plants were able to support the spotted lanternfly only for a couple more days past having no food at all.
And that does not suggest that they are a very good secondary host.
However, grape vine and tree-of-heaven, the individuals, the majority of individuals, at least half or more of the individuals survived 'til the end of our study, when we called it at day 12.
We actually went past this, to day 20, just to see what would happen.
But we didn't do that for all of them, so I'm not showing the data here.
And the grape and the Ailanthus all survived way on out to day 20 as well.
Honeydew and sooty mold production on the sleeves was significant.
You can see here, this is after the 12 days in the field, of one of our tree species, I don't see which one that is, but probably the birch it looks like, there's very little damage done to the sleeve.
Whereas, out here, on the tree-of-heaven, there's a lot of sooty mold growing on the inside of the sleeve, and the sleeves are just dripping with the honeydew from the Ailanthus, from the spotted lanternfly.
So to wrap up here, we have a couple of conclusions to support the Pennsylvania Department of Agriculture's management plan.
Immature spotted lanternflies are broad generalists, and they will likely be able to impact a number of different North American plant species.
The extent to which they do that is still unclear.
The adult preference for Ailanthus is gonna allow us to target management opportunities.
This is already happening.
And it turns out, we support that as a good idea.
Wild grape appears to be a suitable secondary host.
And the wild grape is likely gonna act as a refuge, a place where the spotted lanternflies can hide out when the Ailanthus altissima is dormant or if it's been removed from a certain area.
Now, what's still unclear, and what we'd like to discover next year, is can spotted lanternfly live on grape and complete its entire life cycle?
That's still unclear because a number of our grape extension workers have been trying to rear spotted lanternfly in the laboratory on grape and not having a great deal of success.
So it's possible that they may be able to get nutrition from the grape and then have to move to the Ailanthus to trigger some sort of developmental pathway that leads to production of eggs or development into the next larval stage, or maybe even the adult stage.
It's still unclear what that is, and that's, remains to be seen.
But it is also clear that other trees, other non-Ailanthus trees in Pennsylvania, can be utilized in some way by the spotted lanternfly.
And those are going to have to be continually monitored as we remove Ailanthus as a part of the management plan.
So as we begin to take away the Ailanthus, we need to keep an eye on it and see if, you know, are they now hitting the maples, which could be a problem.
So we'll continue to watch that.
Lots of people to thank, and I appreciate you listening to my presentation.
If you have any questions, please get in touch with me.
I'm available at the information at the beginning of this talk.
Thanks very much.
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