Pests vs Beneficial Insects

Thomas Whitney, technical advisor from the Davey Institute, shares some of his knowledge on different types of pests and beneficial insects. 

In this episode we cover:  

• What defines a pest (0:47)
• Pest classifications (1:45)
• The worst pest for trees (2:30)
• Which pests homeowners notice the most (4:16)
• Types of leaf chewers (4:52)
• Types of woodborers (5:56)
• Emerald ash borer (6:30)
  • Thomas' first encounter with EAB (6:37)
  • How to deal with EAB (8:47)
  • Is the EAB here to stay?  (10:41)
• The importance of tree diversity (11:30)
• Beneficial insects (12:30)
  • Predators (12:57)
  • Parasitoids (13:06)
• The balance of good bugs and bad bugs (13:57)
• Thomas' entomology journey (15:12)
• Thomas' research on linden trees(19:41)

To find your local Davey office, check out our find a local office page to search by zip code.  

To learn more about the emerald ash borer, read our blog, The 101 on Emerald Ash Borer.
To learn more about woodborers, read our blog, Signs of Tree Boring Insects

Connect with Davey Tree on social media:
Twitter: @DaveyTree
Facebook: @DaveyTree
Instagram: @daveytree
YouTube: The Davey Tree Expert Company
LinkedIn: The Davey Tree Expert Company 
 

Connect with Doug Oster at www.dougoster.com. 

 
Have topics you'd like us to cover on the podcast? Email us at podcasts@davey.com. We want to hear from you!    

Transcript

Doug Oster: Welcome to The Davey Tree Expert Company's podcast, Talking Trees. I'm your host, Doug Oster. Each week, our expert arborists share advice on seasonal tree care, how to make your trees thrive, arborists' favorite trees, and much, much more. Tune in every Thursday to learn more because, here at The Talking Trees podcast, we know trees are the answer. I'm joined this week by Dr. Thomas Whitney. He's the technical advisor for the Davey Institute. He's up in the Pacific Northwest and for Western Canada. Welcome to the show, Thomas.

Dr. Thomas Whitney: Hey, Doug. Good to meet you and happy to be here.

Doug: Nice to see you. We're talking all about good bugs, bad bugs, and what they do with our trees. I want to start off by just asking you, how do you define something as a pest?

Dr. Whitney: That's a good question. First, I'd like to say, there's no such thing as a bad bug.

[laughter]

Dr. Whitney: Pests, how do we define them? Well, it really is a human exercise, I'd say, in trying to designate what organisms affect things that we as humans value, right? You can have termites that affect structures. We obviously value those structures. Pests can also affect ecosystems, so forestry pests. Those resources that we may draw on for lumber, those are of our interests, and pests diminish the value of those. Then on the flip side, which maybe we'll get to soon, there are those beneficial pests that enhance our interests as well.

Doug: When you're breaking down these pests as far as affecting trees, how do you classify them?

Dr. Whitney: Good question. Almost always, we're talking about herbivores. These are insects that derive their nourishment from feeding on plant matter. We can break down pests into three main categories. We have the leaf chewers. We also call them defoliators. The second group, we call sap feeders. They're feeding on the sap of the trees. The third group are wood-boring insects actually, make their way inside the tree and feed on the internal tissues.

Doug: Of those three, is there one that's worse than others or, I guess, it just depends on the tree, depends on the climate, depends on the infestation, right?

Dr. Whitney: In this case, we can make some broad assumptions here and say that wood-boring insects are, by far, the most severe for the health of the tree. If you think about leaf chewers and sap feeders, they're both interested in reaping the spoils that the tree produces. The trees are going to undergo photosynthesis, produce those nutrient-rich sugars. The leaf chewers are going to go straight after those chlorophyll-rich leaves and diminish the tree's ability to produce those sugars.

It's detrimental, reduces the vigor a little bit. The sap feeders are bypassing that whole system and going straight for the end product. They're going straight for the sugars and extracting those sugars. Again, that's diminishing the vigor a little bit too, but a little bit of robbed sugars isn't going to kill a tree. Now, with wood bores, on the other hand, they have a taller task.

They need to penetrate the stiff defenses of a tree, get inside the bark. If they're able to establish, they're actually destroying the plumbing, the vascular system of the tree, and mitigating the ability of that tree to move those water and nutrients up and down. That's when we really start to see branch die back in the tree and slow and steady decline of its health.

Doug: That does sound nasty, but I would assume, and you tell me if I'm right or wrong, are the leaf chewers the things that homeowners notice the most?

Dr. Whitney: Yes, exactly. They're the most conspicuous, at least when we're talking about symptoms and also just seeing the organisms themselves. A defoliation event is pretty noticeable. Maybe sap feeders are a little less noticeable, but they're more sessile organisms that are going to stay put, keep those straw-like mouth parts inserted into the plant tissue for a long time. You may notice things like aphids or scale insects.

Doug: For the leaf chewers, would caterpillars are we're talking about or could it be something else? I'm trying to think in my head. I'm thinking caterpillar.

Dr. Whitney: Absolutely. Caterpillars are a huge one. Again, caterpillars are the juvenile stage of moths and butterflies. You also get sawflies, which are not flies. Sawflies are the larvae of wasp-like organisms. There's also a lot of beetles that are leaf chewers. In your neck of the woods, you got the Japanese beetles, super-important exotic species, but then also you get some natives as well that feed on both the larvae and the adults feed on leaves.

Doug: How about a couple of nasty wood-borers that you deal with?

Dr. Whitney: Oh, boy, that's a good question. The obvious choice is the invasive emerald ash borer. You get these wood-boring insects that the adults lay eggs on the outside of the stem of the trees and it's the larvae that hatch in those eggs. They have the task of going inside, initially boring into the tree and then wreaking havoc, but then you get bark beetles. Out here, there's the western bark beetle. Down maybe where you're at, you get the southern pine bark beetle that is making its way up. It's expanding its range into New England actually. In the cases of bark beetles, it's the adults that bore into the tree initially, and then they make galleries and lay eggs inside those galleries.

Doug: I want to go a little bit off-path here and continue with the emerald ash borer. For somebody that's in your position, talk about the first time you heard about the EAB and then watching the devastation come your way.

Dr. Whitney: I'm glad you asked that. I have pretty unique perspectives because I was in Kentucky for a few years, starting in 2011, when the emerald ash borer was really just starting to get established. I remember as a young entomologist in grad school learning about this pest, and then in the summer of 2012, seeing these beautiful shade trees that were planted on the streets, maybe about 20 to 40 years old. Over the summer, we're just starting to flag branches, die back.

Me and my buddies who would actually-- this isn't Davey-approved, so the safety department, don't get angry with me. As a young kid, we'd climb up the trees and look for the adult beetles. We'd see them up there starting to lay their eggs. Then, in 2015, I moved to Georgia. That's happened to be the time when the emerald ash borer was arriving in that part of the country. I saw that invasion front happen again. I was like, "Wow, I've seen this movie before." Well, fast forward to 2020, I start at Davey out here in the Portland, Oregon area.

Just last June, June 30th, 2022, what happens? The emerald ash borer arrives in Portland, Oregon. It has caused mass hysteria out here. Now, the entire West Coast is on high alert because we have a native ash, the Oregon ash, that's super important in cooling down our riparian areas, salmon, steelhead habitat. You have the whole olive industry in California and olives are susceptible. It's bad news. That is a pest I am all too familiar with. All we can do is hope to slow it down and buy ourselves a little more time.

Doug: Since that early introduction or discovery of this pest, have we been able to figure out anything to deal with it?

Dr. Whitney: Yes, we've made a lot of strides. Unfortunately, when you talk about wood-boring pests, I mentioned earlier that they're, by far, the most severe and devastating for tree health. However, they require a stressed tree to initially establish more often than not. They need those defenses to be down in order to penetrate the bark initially and set up shop. Emerald ash borer is different. It attacks healthy trees.

No matter what the tree is doing, even if it has the most sterling landscape management strategy in all the best cultural practices, it is no match to emerald ash borer. Luckily, though, we've really improved our chemistries over the year. Now, the gold standard is to inject these trees with a chemical called emamectin benzoate, which gives us a two-year protection. It's a systemic insecticide.

The insecticide will translocate throughout the tissues of the tree and remain in those tissues for two years so that when those adult emerald ash borer lay eggs on the bark and those larvae hatch and try to bore into the tree for the first time, they will also be consuming a little bit of that pesticide and then die. For the trees that we want to preserve, especially the really large specimen trees, we need to be doing this every two years pretty much indefinitely, unfortunately.

Doug: There is hope back here that ash trees that are resprouting will be able to grow again, but no one knows. Will the emerald ash borer still be here or has it moved on to the West? No one knows what's going to happen.

Dr. Whitney: Unfortunately, I think that the emerald ash borer has become an endemic resident of our continent now. I'm skeptical that ash will make such a comeback. We've seen this movie before with American chestnut, chestnut blight, elms, and Dutch elm disease. It's unfortunately something that we're just going to have to live with. I just pray that we don't see something that kills off all our maples because dang near all of our urban canopies are planted with maples. It seems like we just moved on and haven't learned this lesson of diversity in our urban canopies. That's something that could really help.

Doug: Again, before we move on, let's talk about that lesson that we should have learned. On this podcast, I hear it a lot from arborists and scientists. Diversity is everything, isn't it?

Dr. Whitney: It sure is. It's a form of bet-hedging. If you have a lot of different kinds of trees and one pest or disease comes along, maybe an invasive, and wipes out a whole subset of those, then if you have a diverse canopy, you don't lose that much. That's the idea. It's quite simple.

Doug: All right, let's get on to something a little bit more pleasant. How about beneficial insects? There's good guys out there.

Dr. Whitney: That's right. Of course, just to remind you, this is all based off of our human perspective of what is beneficial or not. That said, yes, there's a whole group of insects that we deem "natural enemies." These include the predators and the parasitoids. These are the insects that attack the pests, the herbivores. Predators are actually capturing and feeding and consuming on those live pests and killing them outright. Then the parasitoids, I'm sure they've been brought up on your pod before.

For those who are unaware, this is the movie, Alien, drew inspiration from these real live organisms. What they do is these are mostly wasps and some flies. They capture their prey, their pest insect. They insert an egg either on top or inside of that live insect along with some venom and some antibacterial and antiviral substances to keep the insect alive as an egg incubator. That egg hatches and the larvae feeds on the live insect from the inside out. The end result is the same as predation where that you kill an individual pest. It just takes a little longer and it's a little more extreme.

Doug: Yes, we see it all over the garden, parasitic wasps, and they're definitely a positive. Like you said, it is from our perspective. I think that's really interesting to look at it that way because when I kicked it off with good bugs and bad bugs, it depends on who you ask. Mother Nature is doing her thing putting a balance together. People think of a yellow jacket as a bad bug, but it serves a purpose in nature.

Dr. Whitney: Yes, absolutely. Yellow jackets are actually predators sometimes too. They can actually feed on pests, so it really does depend on your perspective. Even the emerald ash borer that we were talking about, Doug, it's not its fault that it was brought over here in Michigan in 2022 or, sorry, 2002. Over the long haul of ecological time, I'm talking tens of thousands of millions of years, it's going to reach a new equilibrium and whatever new ecosystem happens to be here. You're spot-on.

Doug: Tell me a little bit about your journey to this position that you're in now. Where does it begin?

Dr. Whitney: Well, as many entomologists say, I became an entomologist by accident sort of. [chuckles] You kind of fall into it. I was a biology major in college at Gonzaga University in Spokane, very interested in ecosystems, ecological interactions. Quite broadly, ecology, the interaction between the living and the non-living environment. I got this summer job with the USDA Agricultural Research Service in Corvallis, Oregon, working on pests of small fruit crops.

Think weevils that attack the roots of strawberry plants, for instance, or the spotted wing drosophila that lays eggs inside of blueberries. I found that, "Hey, you don't have to do any ethics paperwork surrounding these organisms. People don't really care if you study them or even kill insects, so it's a really good model organism to study ecology." I ran with it and I did a master's of entomology at University of Kentucky.

I was actually researching spiders. I was looking at predator-prey interactions of woodland wolf spiders. I would go out every week by myself with a headlamp on in the middle of the night and look for spiders. The reason why you do that at night is because wolf spiders have these iridescent eyes where if you shine a light on them, they'll sort of reflect back on you, so they're easy to spot.

I'd collect them and I was doing molecular gut content analysis. I'd essentially mash up these spiders and use PCR, similar to what we test COVID with, to test for certain prey that they may have been feeding on. The question there was, how does their feeding change throughout the season? These are winter-active wolf spiders. That was a broad ecological pit stop in my career. From there, I wanted to do more problem-based applied research, more to do with pests and plant-insect interactions.

I found this program at University of Georgia in Athens, where I was looking at a scale insect. This is the eastern white pine bast scale. It was, at the time, fairly novel and new to be finding it so prevalently on eastern white pine. It was associated with this canker disease called caliciopsis canker on eastern white pine. My job was learning more about the scale insect. Probably, my most impactful data chapter out of that dissertation was doing population genetics to determine if this was an exotic species or not.

We found that it's native and behaving in unusual ways. I think my dissertation just opened a can of worms and more questions arose. My last stop before coming to Davey, this was my stepping stone into the ornamental tree world, is I got a postdoc at Washington State University in Puyallup. This is outside of Tacoma, so it's on the western side of the Cascade Mountains. I was working on pests of Christmas trees, so I was doing a lot of young conifer pest research.

I was learning a lot about diseases as well because they deal with a lot of diseases and these conifer monocultures that they grow out there. Pandemic hit. Davey job came up. Wow, what a cool gig. Being able to travel around and serve as an extension agent for this company has been a real thrill actually. I've learned a whole lot. To get paid to learn and enrich myself is pretty much the best job I could think of.

Doug: Well, tell me a little bit about the research that you're doing right now with linden trees.

Dr. Whitney: Yes, good question. We were talking about these natural enemies. They are all around us. They're ubiquitous in the urban landscape, but sometimes they lose the battle or they're just not quite effective at bringing down pest populations below a threshold that we see as adequate. What I'm doing out in Portland is using biological control. It really hasn't been explored too much in the home landscape outside of small garden scenarios. Maybe you're familiar with this, Doug.

The idea is to augment the population of natural enemies, providing more supplemental individuals to try to turn the balance. What I'm working with, I'm working with the city of Portland and working on their street trees. They have a nice online street tree inventory. The legal designation of the street trees are, it's the city's property, but the homeowner needs to take care of it, kind of a raw deal for the homeowner. It's a good Petri dish for us to work in.

Linden trees are notorious for getting aphids. Aphids are pretty benign pests. They decrease the vigor a little bit, unless you've got a really bad infestation, but they're more of a nuisance pest. They drop that sticky honeydew, gets on your cars, on your patio furniture, things like that. Some people want the nuclear option to get rid of it. "I don't like the honeydew. Come spray my trees. Come do a soil injection of a nasty systemic insecticide."

Especially for something like a linden that flowers and is so bee-attractive, we'd like to get away from some of those chemical management strategies if we can. The idea here is asking the question, "Is there a biological control option that we can deploy that actually is effective on single landscape trees?" We found a product that we think is interesting. It is an insect called aphidoletes. It is a midge, a little fly, similar to a little mosquito you'd see buzzing around. These flies are-- number one, they're pretty weak flyers. They're not like lady beetles that'll just fly away as soon as you release them.

Number two, they're highly attractive to that aphid honeydew. They'll seek it out and lay their eggs right where the honeydew happens to be present. Number three, lastly, the larvae that hatch from those eggs are voracious aphid predators. They'll go after those suckers real hard. We're going to see. We hope that this product, it's a little vial of 250 individuals hung on a tree early in the season where aphids are active. We're hoping that can provide some early season control and hopefully mitigate the amount of honeydew that we get on those trees.

Doug: Tell me just a little bit more. If I had a big tree, how many of those vials would you think you'd be hanging? A lot of them or just only needs one and then they keep spreading and spreading?

Dr. Whitney: We're starting with the lowest amount possible. There's two schools of thought. You can either do early-season control or later-season severe knockdown. Once you've waited late in the season, the aphid population has already exploded. It's an exponential growth curve at some point, then maybe you need to put out lots of insects. If you can hit them early, we're hoping to flatten the curve as it were and hopefully, over the course of the season, not explode to those high numbers in the first place.

Doug: How does that feel to be working on something like that? It's so positive. It's like, "Okay, we don't have to use chemicals. We can use this insect to deal with that insect." That's got to feel great. [chuckles]

Dr. Whitney: It does feel great. The asterisk, I will say, is this particular predator has proven efficacy in settings like greenhouses and then highly-controlled outdoor, monocultural ag situations. The fact that we're in uncharted territory here is a little bit anxiety-inducing because it may not work, but that'll be good. This is what science is all about. You need to rule out these low-hanging fruit in order to move on to other strategies.

Doug: Well, Thomas, this has just been so enlightening. I just appreciate your time. Just great stuff. We're going to have to talk again because I think we only scratched the surface. I probably have 20 more questions. Thanks again for your time. We will set up another time to talk.

Dr. Whitney: Happy to do it, Doug. Thanks so much.

Doug: Well, I hope you found that as fascinating as I did. I can't wait to talk with Thomas again for the show. Now, tune in every Thursday to the Talking Trees podcast from The Davey Tree Expert Company. I am your host, Doug Oster. Do me a big favor. Subscribe to the podcast so you'll never miss a show. If you've got an idea for a show or a comment, send me an email to podcasts@davey.com. That's P-O-D-C-A-S-T-S-@-D-A-V-E-Y.com. As always, we'd like to remind you on the Talking Trees podcast, trees are the answer.

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