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# Understanding Tree Pests: Disease Interactions, Invasive Threats, and Management Strategies

## GTBOP Green Industry Series — January 15, 2026

Speaker: Dr. Ignazio Graziosi, Assistant Professor, Warnell School of Forestry and Natural Resources, University of Georgia Moderator: Dr. Bodie Pennisi, Horticulturist, University of Georgia Duration: 52:11

## Introduction

Bodie Pennisi: Welcome back, everyone. Our second speaker is Dr. Ignazio Graziosi, who is an assistant professor in Warnell School of Forestry at University of Georgia. Dr. Graziosi studies tree health and raises awareness of the benefits provided by trees. As a field biologist, he has studied the impact of invasive species — insects and microorganisms — on tree health and used this knowledge to develop management and surveillance tools while engaging land managers and the public in education programs. In his early career as a forester, he focused on the management of natural and urban trees. Dr. Graziosi has held positions with non-governmental and governmental organizations, universities, and private companies in different countries. His work involves field and laboratory studies, data collection and analysis, development of protocols, use of photography, team project and partnership coordination, capacity building, education, and outreach. And Dr. Graziosi, the floor is yours from Italy.

Ignazio Graziosi: Thank you. Thank you, Bodie. Good afternoon, everybody. Give me one sec that I'm going to click the magic button. All right. Can you hear me all right and see my screen? Fantastic. It's great to be here. Thank you again.

## The Disease Triangle

So we are all dealing with a variety of different tree pests. You can see on the screen a couple of examples. There is a woolly adelgid. We have fall webworm, caterpillar, beetles, scales — and we tend to concentrate on the pest itself because it's what produces damage to our trees. But it is important to remember that it is always a team result. We have the pest, yes, but there are other actors in the picture that cause the overall damage. Of course, we have the tree itself and we have the environment. And the damage on the tree, the damage from the pest and from the disease, is caused by the interaction of these three components. And this is the concept of the disease triangle. So the damage is not caused by just one component. The pest alone is not enough, but it is the interaction with the tree, which for example is susceptible, and the environment. And we are dealing with trees, especially in the landscape, for the focus of this webinar, and in urban environment. And in those environments, the situation gets worse.

## The Spiral of Tree Decline

And I introduce to you the spiral of tree decline. And this is a diagram that was developed in the 90s and is really useful to understand this concept one step more. So how does this diagram work? You see three different levels of spirals. Each spiral is a family of factors that add stress to the tree at different levels. A lot of those are similar to the stressors that Dr. Klein presented at the beginning of his presentation. And all these different families of stressors, they end up eventually with the death of the tree. And you see at the center of the death spiral, there is in fact the death of the tree.

And if we look at those three spirals one by one, we can see, for example, the first one that is called the predisposing factor — general stressors. The urban environment of course is stressful for the tree, there is the genetic potential of the tree itself, and again it's a demonstration that the disease triangle is really important. And then we have well-known stressors like soil compaction, which is often the number one issue for many trees. And then we have another spiral that is closer to the center of our death spiral, which is called here inciting factor, and we have defoliating insects, for example, we have drought. And then we have an even more internal spiral which is contributing factor, and you see a lot of biotic factors. You have fungi, wood-boring insects, nematodes, Armillaria for example.

The important thing to understand of this diagram is that each of the spirals — the predisposing factor, the inciting factor, and the contributing factor — contain factors that can directly bring the tree to death. If you see, I'm not sure if you are able to see my pointer that I'm using on the screen.

Bodie Pennisi: Yes, we are.

Ignazio Graziosi: Fantastic. Thank you, Bodie. And you can see these lines here. These lines mean that each of these factors — for example, urban environment alone or soil compaction alone — are able to cut through the different layers of the spiral and bring the tree directly to death. One important message to take home from this diagram is that the health of the tree and potentially the death of the tree is an interaction between many factors.

## Native and Non-Native Pest Interactions

And if we go back to our slide visualizing different pests that we have to deal with, we have here non-native pests. We have examples of native pests. We have examples of native trees, examples of also exotic trees. And understanding the interaction among those — native pests attacking native trees and vice versa, non-native attacking native and native attacking non-native — is really important because it allows us to understand the mechanism and to understand what are the general strategies we can use to manage and control those pests. And this is true for many different pests.

So I'm bringing to you three examples, three stories if you want, that investigate, explore different scenarios and present to us some important components of this interaction that will help us to deal in the future with a variety of different pests.

## Example 1: Emerald Ash Borer — A Non-Native Pest on Native Trees

So the first one, the first example, the first story for you is a native tree impacted by a non-native pest. And this is the very famous case, the superstar of insect pests, the emerald ash borer. So the emerald ash borer — I'm sure many of you are familiar with it — on the picture on the left is a canopy dieback caused by the insect. And remember, when you see canopy dieback caused by the emerald ash borer and you identify the problem to be that, the emerald ash borer, that means that the insect has been spreading in the area for at least 5 to 10 years. And then you see on the right that is the damage at a stand or forest level.

### EAB Life Cycle and Damage

So a very quick summary of what the EAB, emerald ash borer, is about. Larvae feed under the bark and doing so disrupt the phloem, the cambium, the outer xylem, and it cuts off the movement of nutrient and water. And trees, they can die very fast. This is an overview of how the damage happens. And if you start from the picture on the left, you see a young tree that is debarked, and you see the gallery caused by the feeding larvae, and you see that the tree is desperately trying to sprout. It has a reaction to the attack, and the water sprouts are actually a very important diagnostic feature in order to understand if a tree is attacked by the emerald ash borer.

And if you get closer to the tree, you can actually see the larvae, like here, that is feeding. This is a fourth instar, is a mature larva, is probably around two inches long. And by feeding, it basically disrupts all the cambium tissue and the outer xylem. And then, after the larva completes its development, which is usually at the end of the season, it folds in a J-shape and gets a little bit deeper in the outer wood, and it starts kind of sleeping, and overwinters as what is called a J-larva, or prepupa. And then at the end of the winter, it pupates and emerges in spring. You can see the shiny green beetle that is emerging from a tree. And while it emerges, it leaves a very characteristic, the famous D-shaped exit hole.

This is another way to represent the life cycle of the insect. We can start from here, where the insect again comes out from the tree, leaving the D-shaped hole, and then mates. The female lays eggs in the cracks of the bark. From the egg, a larva hatches, goes through the bark and starts feeding and causing the galleries you already saw in the previous photos. And then it pupates and will emerge again the following year.

### Generation Time and Temperature

Here it is important to remember that this is usually mostly a one-generation-per-year insect. But there is always a part of the population of the emerald ash borer in any location that requires two years instead of one to develop. And this is true especially in the northern part of North America, where temperatures are lower. As we know, temperature usually increases the development of insects. And so the colder it is, the slower it develops. So at northern latitudes in North America, a larger part of the local populations of emerald ash borer requires two years to develop. And it is important to know when we have to deal with this insect to control it.

### Spread Across North America

It was found, was discovered in 2002 in the Detroit area, which means again, as I pointed out earlier, it was present in the area already for at least 10 years. And then you see all the little red dots. Yes, it took North America, as we know, by storm. This is one of the last available maps from USDA. This is 2023, because in 2021, I believe, the quarantine was lifted at federal level. It was lifted because there was no hope to contain the insect through quarantine.

And then the invasion of North America by the EAB was caused by one single individual cause. There was one culprit that allowed the EAB to move so quickly all over the United States. And I let you guess — you can write your answer if you have an idea in the chat box. I will not be able to see it right now, but I will go later and check.

And this is, of course, firewood. Campers and travelers, they move infested firewood to the next city, to the next county, to the next state. And this really is what determined a lot of the pathways of the invasion in North America. They were able to connect very closely the pattern of the spread with the highway and freeway system. There is one good thing that came out from this disaster, which is the "Don't Move Firewood" campaign. This is a very effective and important campaign that helps, for example, contain other invasive insects, such as the Asian longhorned beetle.

### EAB in Georgia and Ash Species Diversity

Okay, so we know that as the EAB spread in North America, it attacked and impacted heavily the native species of ash. In Georgia, for example, there is of course the emerald ash borer, and this is a spread — I would say the southern edge of the invasion, so it's still spreading. This map is from 2020. So there is active surveillance, it's present in the Athens area of course, and even a little bit further south. So you may think that it's not very important, is not as important as fighting against the emerald ash borer in Georgia compared to other states. It's true, there are other states where there is a continuous presence and availability of ash, and Georgia is more scattered. But if we start looking at the distribution of ash species in Georgia, we see that it is really important for biodiversity and actually the state hosts multiple species of ash. We have green ash statewide, we have blue ash, which is an interesting tree because it shows a little bit of resistance against the emerald ash borer — it will die eventually, but it will take way longer compared to other species of ash. We have white ash, Carolina ash which is a southern ash, we have Biltmore ash which is a subspecies of white, we have pumpkin ash on the southern part of the state, swamp white and small ash.

### White Fringetree as Alternate Host

And then there is another plant that unfortunately is important for the ecology of the emerald ash borer, and it's a surprise that happened in 2014, when they discovered that the EAB was able to expand its host range and attack a native plant in North America, which is the white fringetree — which is the same family, Oleaceae, as ash. And this is present also in Georgia. It's important to know that because not only could it be a damage for the white fringetree, but more importantly, the white fringetree could function as a reservoir for the population of the EAB, even though all the other ash trees in the area are gone. So the EAB can stay in an area utilizing the white fringetree.

### Global Trade and Non-Native Species

Okay, so we know that the EAB is non-native and we know that it is from Asia. So if we look at the map where it was in Asia and where it is now in North America, spreading and causing damage, we may ask — how did it get there? Of course we know, through trade. This is a photo in the port of Savannah. And we know that this accidental introduction through trade of non-native species is not a new trend, but is an exponentially increasing trend. And you can see here an example from different parts of the world. So it is really exponentially increasing. One reason is that our ability to detect species has increased as well, improved. But trade is increasing, of course, and the introduction of non-native species is reflecting this globalization.

If you go near potential ports of entry, such as airports and ports, you may notice traps. This is a generic trap in the port of Savannah. This is another example since we are talking about the EAB. This is the trap that is designed to catch the EAB — it's a series of interconnected funnels. There is a pouch, which is the green pouch there, that is a lure that produces an attractant for the EAB. The EAB arrives, hits the funnel, and it falls in the cup. These types of traps, they are not designed to catch as many beetles as possible to remove them from the environment. It's just a detection, but it's a very important detection methodology.

## The Invasion Curve

Okay, we know of the damage, as the EAB spread in North America it caused immense damage to the native population of ash. And we have another tool here I want to present to you, because it's a useful tool to understand the strategy to manage non-native and native pests alike, which is the invasion curve. This is a diagram that illustrates the growth of a population of a pest, which here is called pest prevalence, over time.

So the story starts with the introduction, when the pest arrives in the area. After the introduction, of course, the population of the pest, the prevalence, is still low. And then it starts growing and start multiplying and feeding on the host. And then it enters exponential growth. And this is when land managers, for example, start to be aware. And it's a little bit more time before the public starts to be aware. And by the time the public starts to be aware, usually the population is already really high until it reaches a plateau which is the so-called carrying capacity — what is that, for example, is where or when all the ash trees in the area are gone, so the population of the pest cannot grow anymore.

This diagram is important because it can be connected with our ability to deal with and control the pest. When the population is really low, right after the introduction, we can even try to eradicate a pest. Of course, it's very difficult, but in some cases, for some pests, it's not impossible. We can do prevention, for example. But then as the pest prevalence starts to grow, it's really impossible to eradicate. And then the only control that is possible is a local control — for example, just trying to save individual trees. But as the prevalence and the difficulties of controlling a pest grow, the cost associated with the control grows as well. And this is really important to understand. And this is why detection is so important, and ideally we want to have effective tools to detect a pest as close to the introduction event as possible, because everything is easier and is possible.

## Why EAB Is Not a Pest in Asia

Okay, so as we understand how an invasion works, we can look at the map again and we can ask ourselves — okay, we know that the emerald ash borer is non-native, is from Asia. And it's a pest here, but what about in its native range? What about in Asia? Was it a pest? The answer is no. And there are multiple reasons for that, and they will relate to our disease triangle.

The first reason is that the native species of ash in Asia, they say, co-evolved with the pest, which means they are less susceptible or resistant. And the only ash trees — Asian species of ash trees — that can be attacked by the EAB in Asia are very weak and stressed trees. That's one important reason. And this is why one of the approaches to control the EAB is to artificially make them resistant through chemical protection.

### Chemical Control for EAB

Of course, this is just a visual summary of the technology that I'm sure you are familiar with. There is tree injection, bark spray, and soil drench. I want to give just a little flash and overview of the chemical control methodology for the EAB. And there are a few involving systemic insecticides. Some of them can be applied by homeowners. Some of them, of course, need a professional applicator. And you have to choose carefully which one, depending on the season — for example, soil drench needs to be applied in the spring before leaves are out. I leave you here two links, two QR codes. I encourage you to check them. One is an overview of the status and the control of the EAB in Georgia. And the one on the bottom on the left is the full protocol for insecticide control for the EAB.

### Importation Biological Control

Okay, we are still trying to answer our question — why is it not a problem in Asia? One reason is the trees are resistant, but there is another reason. The other reason is that the population of the EAB there is kept in check by a community of natural enemies. These are predators, are parasitoids — and we will see later what a parasitoid is — that are able to attack the EAB and to keep the population low.

Okay, so why don't we bring them over? That's exactly what we did. And this is called importation biological control, where you go there, you study the natural enemies that are effective in the native range, and you bring them over. USDA did that after risk assessment and introduced a few different species. And you see here three tiny wasps. Those wasps are parasitic wasps, or parasitoids. The first two, the one on the left and the one on the center, they attack the larvae of the EAB. The one on the right attacks the eggs. And those are specialists. What that means is that they only attack the EAB. They don't attack any other insect. And so this warrants success in a way, because they cannot start attacking another insect and kind of waste their potential.

How do they work? Okay, let's start with the first one here, the one on the left. And you see it's a small wasp and has a kind of a long tail. Its tail is an ovipositor, and it uses its ovipositor to find trees that are infested with the EAB and drill through the bark. It is able to use vibrational cues to understand if there is a larva under the bark and exactly where it is, and it stings the larvae of the EAB and it puts its own eggs in the larvae. Think about the movie Alien — Alien 1, not Alien 3, because the life cycle in Alien 3 gets very complicated — but in Alien 1 is exactly how it works. Inside, there will be the larvae of the wasp that feeds in the body of the larvae of the EAB, eventually consuming the whole animal.

The infographic that you see on the slide is the technology that is used to release it. This is a log prepared in the lab that is filled with larvae of the EAB infested with the parasitoid wasp. You hang them on a tree, the adult wasps will eventually fly out and find other trees infested with the EAB to be parasitized.

The second one is the egg parasitoid. I think you know the story now. It works exactly the same way — it attacks eggs. The technology is a small container. You can see in the picture on the bottom right, it's a drugstore container, called the O-binator. It contains a paper where there are eggs of the EAB that have been parasitized with this parasitic wasp. Look now at the picture in the center. These brown circles are the eggs of the EAB. If you look at the one on the bottom, you can see that inside there is actually a tiny baby larva of the EAB that is waiting to hatch. But if you look at the other two, the dark ones, you see that inside there is something different. That is the wasp that is ready to emerge.

### Native Natural Enemies and the Goal of Balance

Okay, so we understand about biological control now, the importation biological control, but you may ask — okay, so we are in North America. What about our native natural enemies? The answer is yes, we have some. There are many species that have been described of parasitic wasps or other types of insects, but those are not specialists. They can attack also other types of insects. So they are not effective in providing — they cannot be the only ones that can provide control. Alone, they are not enough.

So at the end of the story, what we want to reach for the EAB, and in general for many non-native pests attacking native trees, is balance between the susceptibility of the plant and the community of natural enemies — both native natural enemies and also biological control. But also in the picture there is the chemical protection that is really important, especially to save trees of great value. Because it's true that biological control in North America for the EAB hasn't been fully successful yet, but we can still save large trees of big value in the city and the landscape using chemical protection.

## Example 2: Crapemyrtle Bark Scale — A Non-Native Pest on Non-Native Trees

Okay, so we are ready for our second example — a non-native tree that is attacked by a non-native pest. And this is an example that may be relevant for us in the South, which is the crapemyrtle bark scale.

So the crapemyrtle bark scale — you can see here in the center — is of course a non-native scale attacking our beloved crapemyrtle. There is a huge crapemyrtle culture in the South. There are hundreds, I think, of different cultivars belonging to different species — it's not only Lagerstroemia indica, but there are hybrids of different species, different color, flower, texture of the bark, size. And of course, it's easy to be judgmental toward the crapemyrtle because it's so commonly used and you can say it's used too much. It's true. It's easy to be judgmental, but it's important to remember a couple of things. One is that crapemyrtles provide benefits. And you can see here a little report that has been prepared using this tool called iTree. If you are not familiar with iTree, it is a suite of different tools that can be extremely useful to calculate benefits, so-called ecosystem services of trees, but also can be used to select the right tree for the right place. The second reason is that regardless of how much the crapemyrtle is planted in the South, we have to deal with this pest because it will create damage. We will have to deal with removal of attacked trees or the control of the pest itself.

### CMBS Biology and Life Cycle

Okay, so the crapemyrtle bark scale, starting from the picture on the left. This is a twig of a crapemyrtle — of course you see the white specks, those are individual, mostly females, of the crapemyrtle bark scale, CMBS in short. Why is it black? Because like aphids, of course, scales while they feed secrete droplets of sugary sap. And so black sooty molds grow on that. On the picture in the center, different things. Those white lumps are mostly mature females of the scale, but you can also see here immature female nymphs. And this is important for the life cycle. On the right you see a female, and if you flip the female you see the eggs. Those very nice pink colored ones are eggs.

The life cycle involves both males and females. The male is actually winged; the female is not winged, and a mature female loses her legs and cannot move. One of the things that complicates control is that it's not clear how many generations there are. They describe up to five generations, but the problem is that they are overlapping. So at one point, at any point, you may find different stages of the insect. If I go back one slide, the picture in the middle here has been shot one month ago in Athens, so in the winter. And you can see there are nymphs and adults. The nymphs are called crawlers.

### CMBS Invasion Timeline

Okay, what is the situation? It was found in 2004 in Texas — of course a huge crapemyrtle culture state — and then in 2014 in Georgia, and only in 2018, unfortunately, was found in nurseries in Georgia. The QR code I put there is a summary of the status and the biology of the crapemyrtle bark scale from UGA. So if you are interested, please snatch that.

### CMBS and the Invasion Curve in Georgia

Okay, so we already know the invasion curve, what it means, and it's really important for the crapemyrtle bark scale. Even though it's already present in the South, even though it's already present in Georgia, to be able to detect it as soon as possible — it's not everywhere yet. In Athens, it got there, I think, in 2021. And you can see it in high numbers on some trees, but there are a lot of trees with very low infestation. So I would say we are at the beginning of the invasion in a lot of places in Georgia. So we are in the situation where we can do well because we are at the point on the invasion curve where the population is not so high that our control can mean something.

### CMBS Host Range in Asia and North America

Alrighty, let's go back to our well-known map. So we know that it is non-native, comes from Asia. So we may ask, okay, what about the host there? The bad news is that this insect in native Asia can feed on many different species of plants. It's not a specialist, so it can feed on apple in Asia, and soybean — it has been found on fig. One good news is that since there are so many, they were able to find some cultivars, some species of crapemyrtle that have low susceptibility. And for example, the species Lagerstroemia speciosa — they are studying this still, though.

Okay, so those are the plants in Asia. What about the plants in North America? We know that it attacks basically most of the cultivars of the crapemyrtle, but unfortunately, like the EAB was able to find the white fringetree, the crapemyrtle bark scale started to feed happily on American beautyberry and also on St. John's wort. So this can be a problem, of course, because it can go around attacking other plants.

### Urban Heat Island Effects

Okay, we are familiar with the disease triangle, so we may ask — okay, what about the role of the environment? What is the role of the environment here? Unfortunately, again, scales are one of the groups of insects that most take advantage of urban heat island. Urban heat island, of course, is the phenomenon that causes temperatures due to hardscape in the city to be even 10 degrees higher. And this has two effects. First of all, it stresses trees and they become more susceptible to pests. Second, it accelerates the development of the insect itself. And scales are very good at taking advantage of that.

### Chemical Control for CMBS

Okay, let's go to some good news — the tools, the weapons we have to control it. So this is an overview, again, of the chemical control available for the crapemyrtle bark scale. We have soil drench, we have soil injection, we have foliar sprays, and also some soaps — they can be used mostly to target crawlers, which again are the small, the young nymphs, like the pinkish one in the photo here. You can see in the table different product brand names and how they can be applied. And I encourage you again to snatch that QR code because it will give you the full protocol that you can use.

The control, the chemical control, is complicated by the fact that crapemyrtle is not good at absorbing systemic insecticide through trunk injection. The chemical moves very slowly, so that is not a viable option, unfortunately.

### Natural Enemies: Lady Beetles and Lacewings

Okay, we know about natural enemies, so we may ask now, looking at our map, what is the situation for this pest? Yes, in Asia, there is a healthy community of predators and parasitic wasps that worldwide and in Asia can attack it. In the US, they were not able yet to clearly find an effective parasitoid, but there are many predators that can feed on the crapemyrtle bark scale, and they are used to try to control it.

So this is my last question for you, if you have any idea of what this is. Okay, so those are eggs of lady beetles, because lady beetles — different species of lady beetles — are avid, hungry predators of the crapemyrtle bark scale. There are three main species: the twice-stabbed lady beetle, the bigeminal lady beetle, which looks like the twice-stabbed but is a completely different species, and also the non-native Harlequin lady beetle. These species will find trees infested with the crapemyrtle bark scale and they will feed on nymphs and adults alike.

So they help — yes, they do help — but often they arrive too late in the season and they are not specialists. They will feed on other prey, which means they will not stay for many generations on the tree, providing continuous control. And that is a problem.

So this is another question for you. This of course is an egg from another predator that would happily feed on the crapemyrtle bark scale. It's called a stalked egg. This is a beautiful egg of lacewings. One species in particular, the red-lipped green lacewing, feeds and predates on crapemyrtle bark scale nymphs and eggs as well. And you can see on the sequence on the right, this is a larva of the lacewing, which are the most voracious. Do they work? Yes, they are actually available commercially, of course, to control different pests including CMBS. But the problem is they don't build up a population on the plant, like the previous case. And also adults need to feed on sugar. And this means that you have to continuously, through the season, release them. So just one release at the beginning of the season is not enough. But they are commercially available and they can be used.

### Balancing Chemical and Biological Control

Of course, you need to do chemical control very carefully because it has the potential to interfere with the biological control. At the same way as for the EAB, what we want in the future is a balance. We want the population of the scale low because the community of natural enemies is healthy, but we want to use and we want to do additional research to find effective chemical control that maybe is more compatible with the natural enemies.

## Example 3: Orange-Striped Oakworm Moth — A Native Pest on Native Trees

Okay, this brings me to the last, I would say, five to eight minutes, which is the last story in my presentation — a native tree impacted by a native pest. And our example is the orange-striped oakworm moth.

So this, of course, is a very well-known pest of oaks, especially red oaks in the group of the red oaks, but can feed on other plants including hickory, birch, and maple. On the left, it's interesting because you can see that the skeletonizing damage is the one that is done by the baby larvae after hatching. And then as they grow, they start feeding on the entirety of the leaf lamina. And in some cases, extreme cases, especially for small trees, they can completely strip a tree. And this tree, the photo on the right, is in early August. And it's a young, but not super young tree. It's a willow oak that was completely defoliated.

### Oakworm Life Cycle and Seasonal Timing

Okay, a little summary — I know a lot of you are already familiar with it — it is of course a late summer and fall season pest that overwinters as a pupa and produces in the South two generations per year. So we can start here. The adults mate and the female lays eggs on the underside of leaves in late summer. And then young larvae initially feed all together on the same branch where they hatched. And then as they grow, they disperse a little bit because they need a lot of leaves. And then again, they can defoliate — in some cases they can defoliate completely a tree, but those cases are quite rare and exclusively for small trees. And at the end of the season, after, for example for the South, the second generation is complete in the fall, with the first cold the larvae drop to the ground and they will pupate in the first five inches in the ground.

### Why Urban and Clonal Trees Are Vulnerable

Okay, so we can use our map as a tool to ask questions. Okay, it's a native pest. Why does it cause or can it cause so much damage? What about the plant? What about the other factors we looked at together earlier for the other two pests?

First of all, of course, it's a pest of particular relevance for urban and landscape trees and young trees. Why? Remembering this triangle — what is the role of the plant? This is an example. A lot of the trees in urban environments are trees that come from the nursery, and so are often clonal trees. The genetic variability of those trees is very low. For example, on the UGA campus in Athens, there are a lot of beautiful Nuttall oaks. But those — they come from, they are very high quality trees, but they are basically the same tree. And so the susceptibility is low. One tree means the susceptibility for all the trees on campus of the Nuttall oak is low. And so they are heavily attacked by the orange-striped oakworm moth.

Okay, what about the environment? An example, again — yes, in urban environments, we have the problem of heat. Again, and we know that it will stress trees, but will help the development of the orange-striped oakworm moth as well. These are some of the reasons why it can be a pest.

### Natural Enemies of the Oakworm

Okay, what about natural enemies? So right now we know all the questions we should ask. Yes, there are natural enemies that have been described. We know of them. There are various predators that feed on larvae — for example, yellow jackets and other wasps. There are various parasitoids and fungal diseases that kill the pupae, up to 10 or in some cases 20% of the pupae. And there are a lot of parasitoids that parasitize the eggs.

And this is important — this is an example. On the picture on the left, this is the underside of a pinnacle leaf full of eggs from the orange-striped oakworm moth. But if we look closely, we see that some of those eggs are yellow. Those eggs are empty eggs. You can see the opening here on the side. They open like a wallet, and the baby larvae already came out, so they hatched. But some other eggs — you can see this one, for example, the dark ones — they have circular openings. That means they have been parasitized. So that is a parasitoid, that is an egg parasitoid, a wasp that emerged from that egg.

### Control Decisions: Damage Thresholds and Btk

Okay, let's talk about control. So since this pest can be a pest but in some cases the damage is not so high, it's important to understand the need for control. First of all, we need to distinguish between aesthetic damage and actual damage for the plant. The threshold is around 25% of defoliation. And then we need to assess the season. Why? Because late defoliation, even if it's very substantial defoliation but occurs late in the season, is not really harmful to the tree, because the tree already stores all the nutrients. So it's not very harmful. So it's important to kind of judge the severity of the situation.

What can we use, though? So we can use Btk, Bacillus thuringiensis kurstaki, as a foliar spray, which is effective, but mostly on young instars — on young larvae. It has very little impact on natural enemies, which is good, but often needs to be reapplied. But there are also other options for contact and also systemic insecticides. I encourage you also here to take a look at the publication linked to the QR code here if you are interested.

## Wrap-Up

With that, I came to the end of my presentation. And I hope I was able to provide you some insight on what are the biological parameters and the ecological interactions you have to look at to understand what is the damage and the control that can be applied to a pest. With that, I think I will stop my sharing and I will take any question you may have. And I will ask your help, Bodie, to summarize any questions that came.

## Audience Discussion

Bodie Pennisi: Thank you, Ignazio. That was great. Lots of really, really excellent information. There hasn't been a question in the chat. There's lots of really good comments. Thank you. I do want to mention something. When you were talking about the crapemyrtle bark scale, unfortunately I have seen much expansion of the pest in landscapes — especially new landscapes, but even established landscapes. I mean, I was in Savannah last year, same tree. At that height, there was no evidence. I mean, again, the tree was pretty high. But this year, we were just there like two weeks ago, and it was right there. And, you know, it was a large tree too. And all across the areas around the plantings, I have visited pretty much — I would say maybe about 60 to 70% of plantings have evidence. So yeah, it's pretty bad.

Yeah, we just have lots of really happy people. So thank you so much again. I know you stayed late to entertain us and share with us your expertise and knowledge. So have fun, be safe, and have a safe trip back to the U.S.

Ignazio Graziosi: Thank you, Bodie. It was my pleasure. I really enjoyed it. And yeah, I'm looking forward to being in touch. Thank you. Bye-bye.

## Closing

Rich Braman: All right, everybody. Thanks for joining us again for the first one of these this year. And we'll see everyone in March. And just make sure you get your sign-in sheets to us at gtbop@uga.edu. And if you need to mail those to us, you'll find that mailing address at the top of the sign-in sheet. I think that's it for me, Bodie.

Bodie Pennisi: Thank you, Richie.

Rich Braman: I'm going to hang around for just a minute to make sure we don't have any procedural questions, but I'll see you soon, Bodie.

Bodie Pennisi: All righty.

Transcript processed for UGA Center for Urban Agriculture / GTBOP Archives Source: Corrected SRT (Stage 1) — GTBOP_Transcript_2026-01-15_TreePests_Graziosi.srt (529 blocks)