Oregon fruit, hazelnut farmers struggling with invasive stink bugs

The brown marmorated stink bug is about the size of a nickel, shield-shaped with five sides and eats almost anything. It’s an invasive species that agricultural researchers, farmers and others have been trying to get under control for many years. The bug is wreaking havoc on Oregon hazelnuts and other fruit trees. Max Ragozzino, a biocontrol entomologist with the Oregon Department of Agriculture, says it’s not a discriminating pest. In their labs, he says, the stink bug feasts on fruits, vegetables and nuts of all kinds, and will even eat jellybeans. Ragozzino joins us to tell us more about the success of recent efforts to control this invasive species, and the ongoing work needed to help the state’s agricultural crops thrive.

The following transcript was created by a computer and edited by a volunteer:

Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller. The brown marmorated stink bug is about the size of a nickel. It is shield-shaped with five sides and it eats almost anything. It’s also an invasive species in Oregon. All of this adds up to a huge headache for Oregon farmers and orchardists and an interesting problem to solve for a biocontrol entomologist like Max Ragozzino at the Oregon Department of Agriculture. He is working on a program to introduce a particular wasp to kill these stink bugs and he joins us now to talk about it. Max Ragozzino, welcome.

Max Ragozzino: Thank you for having me.

Miller: I gave a short description of this stink bug, but hopefully you can give us a better understanding of what it looks like and what it does. What is a brown marmorated stink bug?

Ragozzino: A brown marmorated stink bug is as the name implies, a stink bug. Like you said, the description is pretty accurate for physical description. It’s brown, modeled with two antennae that are striped. That distinguishes it from our other brown stink bugs that we have that are native to Oregon.

Miller: What does it mean to call it a stink bug?

Ragozzino: A bug is a group of insects. In particular, stink bugs all have a piercing-sucking mouth part and a half wing that is leathery. But the stink comes from the fact that they’re, they have a defensive mechanism that really stinks.  If they feel threatened by a predator, they can release a tiny bit of stinky chemical. If you’ve ever picked one up off your windowsill to dispose of it, you’ve probably smelled it.

Miller: I’ve seen, what I imagine, are stink bugs all over the place: in my yard, in fields, [and] often you can go for a walk and they could be all over your pants. What’s the chance that the stink bugs I’m seeing are brown marmorated ones?

Ragozzino: Probably pretty high. Brown marmorated stink bugs are pretty prominent across Western Oregon.  That’s probably because of how invasive it is. Its population has grown pretty much unchecked since it first got to Oregon in 2004.  We have a lot of perfect hosts for it. As you mentioned, it eats a lot. It eats over 100 different plants, including things that we like to grow a lot of in Oregon including hazelnuts [and] pears. When we try to rear them for our research or to help control it, we feed them green beans, carrots, almonds, sunflower seeds, and even jelly beans.

Miller: It eats jelly beans?

Ragozzino: It’ll eat jelly beans. If it’s food, it eats it.

Miller: Well, how are these invasive stink bugs different from the native species that were already existing in Oregon?

Ragozzino: These aren’t actually that different except the fact that these came from Asia. So in Asia, the brown marmorated stink bug acts a lot like our stink bugs in Oregon act in Oregon. They’re a little bit of a pest in particular circumstances. They can be more than a little bit of a pest, but for the most part they are just part of the background complex of pest control for agriculture. But when brown marmorated came over to the United States, it escaped all the things that keep its population in check. So it actually left all of its natural enemies back in Asia and came over here where there’s very little that actually predates it.

Miller: But in the U.S.there are natural predators for the native stink bugs?

Ragozzino: Exactly.

Miller: So what kinds of interventions have farmers tried since 2004 to control this bug?

Ragozzino: Growers have gone through all of the different processes for controlling a new pest when it comes in using conventional insecticides, cultural controls, such as trying to manually remove stink bug eggs when they see them, which is difficult because they are light green on the bottom of light green leaves…

Miller: It also seems like that doesn’t seem like a kind of system that could scale up. I mean, if you have a huge orchard and you’re going to go through looking leaf by leaf looking for tiny eggs, that doesn’t seem to work.

Ragozzino: No. So that is something that people tend to do early on when they first look to see if stink bugs are in their field at all, or brown marmorated sinking in particular. But people have tried trapping methods, other lures, other different types of controls. And we’re coming to the point now–between the biological control program that I’m sure I’ll talk about in a minute with the Samurai wasp, as well as conventional insecticides and other organic insecticides–where the brown stink bug is looking like it can be controlled in a couple of different methods.

Miller: I want to get to those in just a second, but, sticking with the agricultural problem first. You said that they’re generalists and that they eat all kinds of things. What are the agricultural sectors that have been most damaged by these particular bugs?

Ragozzino: When the brown marmorated stink bug first got here, it hit the East Coast first. And within a couple of years it was damaging 90% of the apple crop. It hits tree fruits pretty hard. When it feeds on tree fruits including hazelnut–which is a huge crop for Oregon–it can actually prevent the fruit or nut from growing. Like I mentioned earlier, it has a piercing-sucking mouth part, it’s kind of like a straw. So it sticks its mouth in and actually damages the growing fruit. So if you can imagine something like a hazelnut or a bean, if it sticks its mouth part in and feeds on the inside of that while it’s developing, it actually can cause the hazelnut to grow hollow or wrinkled and malformed. So imagine if you crack into a hazelnut and there was nothing inside, it’s not only disappointing for you as a consumer, but for a grower, it means that it’s worthless.

Miller: And it’s been devastating for jelly bean crops, too.

Ragozzino: Oh, of course.

Miller: [Laughter] Okay, so, so let’s turn to the biocontrol.  You mentioned a Samurai wasp. What is it and how does it act?

Ragozzino: The Samurai wasp is what we call a stingless wasp. It’s a bit of a misnomer. It can’t sting people, but it happily stings stink bugs. It is the natural enemy of the brown marmorated stink bug in Asia and it’s part of the reason why in Asia, brown marmorated stink bug is just a minor pest. It actually hones in on a brown marmorated stink bug egg mass, lays its egg inside a stink bug egg, hatches and eats it alive from the inside. You’ve seen Alien, of course.

Miller: [Laughter] This has been the year of learning about fascinating wasps and I have to say that I now have become a gigantic fan of their fascinating and evil–if you are the wrong kind of egg–ways. How does it know where these packets of eggs are?

Ragozzino: It uses its very sensitive antennae. Actually, there’s a lot of really cool research into exactly that question.  It actually hones in on different volatile smells that come off of an egg mass and it will hone in on that.

Miller: And this particular wasp, it’s not interested in other prey, in other egg hosts for its larva?

Ragozzino: That was the topic of research since 2012. This has been going on for a long time. It takes a long time before we decide to release one of these things outside the laboratory.

Miller: Because it’s a gigantic issue that you’re not playing with but you’re dealing with, you’re really “manipulating” nature.

Ragozzino:  Exactly. It’s a permanent thing that we do. You can’t, you know, “cats out of the bag” at that point.

Miller: And just to play this through, what’s the risk of introducing a wasp like this? If it were something like a generalist, if it were interested in having its babies eat a bunch of different kinds of eggs.

Ragozzino: And that’s exactly why it took from 2012 to 2020 for us to want to mass rear and release these. Researchers actually found more than just the Samurai wasp when they went to Asia. They found many other different insect species that attacked our marmorated stink bug and quickly ruled those out because they attacked other insects. Anything that’s in classical biological control, which is what we call this particular field . . . When they first went to Asia they tested it on other Asian insects as well and for the Samurai wasp they found [that] it looks like it really likes marmorated stink bug eggs. So the Samurai wasp passed the first range of checks. It was brought over to the United States and placed into what we call quarantine labs, or arthropod containment labs, which are run by either the USDA, Animal Research Service or universities such as Oregon State University.

Miller: And what did you find when it was brought there?

Ragozzino: With the Samurai wasps, it was a little trickier than we like. We found that if you gave it the choice between a brown marmorated stink bug egg or any other stink bug egg, it’ll go to the brown marmorated. But if you gave it no choice, if you only gave it another stink bug, it would choose that. So we were actually on the fence about whether or not we wanted to release the Samurai wasp and then nature ….

Miller: Why was that potentially going to be an issue if this wasp was also going to eat native stink bugs? Why might that be a problem?

Ragozzino: So that leads to an ecological cascade, where we don’t know what happens if the brown marmorated stink bug gets pushed down and now it’s just as common as the green or the brown stink bug. We’re thinking about hypotheticals in the 20 to 50 year timeline. What happens if the green stink bug that we have here suddenly gets another natural enemy? And maybe the green stink bug population is lower than it was before we released the Samurai wasp, but we just don’t know the ecological effect.

Miller: So in a sense, as a kind of humility that you have to have, you want to have the fewest impacts possible while still accomplishing the agricultural mission here of helping orchardists and farmers.

Ragozzino: Exactly.

Miller: But it seems like you did decide, despite that risk to native stink bugs and others, to go ahead. So how did you make that decision?

Ragozzino: Nature found its way first. In 2016, long before we were done doing research on the Samurai wasp, we found it in Oregon.

Miller: Wait. Just the same way, although a little bit later, that its prey ended up here with the invasive stink bug, so did these Samurai wasps?

Ragozzino: Exactly. Immediately everyone panicked and assumed that it somehow got out of a lab. We did genetic testing and found out no, it’s actually from an entirely different region of Asia than all the ones that we brought back to the lab, the same species, just from a different region.

Miller: We should say this wasp is 1.5 mm, so it’s like the tiny tip of a pencil. Right?

Ragozzino: Very small. If you saw one fly past your face, you would probably call it a gnat.

Miller: So what’s the best theory as to how this wasp arrived? Where did it hitch a ride?

Ragozzino: It probably hitched a ride inside brown marmorated stink bug eggs. Brown marmorated stink bug lays its eggs on just about anything.

Miller: So they came together is the best guess?

Ragozzino: That’s the best guess. Brown marmorated, it came a few years earlier. And then as we reintroduced brown marmorated stink bugs a couple more times through global trade, the Samurai wasp hitched a ride.

Miller: I’m still slightly confused, though, about the scientific thinking here. Just because the wasps arrived on their own, does that mean that all the care and attention you were paying to, “should we introduce ourselves or not,” goes out the window and now you can just freely introduce more of them?

Ragozzino: Absolutely not. We finished our research. We continued our research on if the Samurai wasp is going to be a pest or a beneficial insect in the United States. And it turns out, luckily, in this case we were leaning towards it looking more beneficial than not. So we think that it’s safe to read the rear and redistribute across Oregon because looking at the research, we found that well, it really does prefer brown marmorated stink bugs. And we weighed the risk benefit there, like you were talking about earlier: the risk of ecological consequences versus the damage to both the environment and also agriculture that brown marmorated stink bug presents if left unchecked. And we decided that the benefit was far greater than any risk to native stink bugs.

Miller: Where does the program stand right now? Have these wasps already been introduced in various places in Oregon?

Ragozzino: Yes. They were originally found a little north of Portland and then now we’ve actually reared and redistributed them to growers all the way down to Medford.

Miller: Has enough time passed where you can actually start to see some results?

Ragozzino: We think so. Right now, anecdotally we have a lot of growers asking, “so is that working because I have seen a lot less stink bugs this year.” That’s a good first sign, but we’re still looking at doing additional years of monitoring to make sure that the reduction in stink bugs isn’t just a one year fluke because of the weather or something like that. That it actually is because of the Samurai wasps.

Miller: You’re talking about a reduction in stink bugs, which seems like an important word here. Is the thinking that once an invasive species like this bug arrives in a place like Oregon that we will be basically stuck with it forever, that it may be a population that could be controlled and reduced, but it’s basically always going to be with us?

Ragozzino: Not every time. We actually have someone on the team who is on our eradication entomologist. There are a lot of invasive insects that come into Oregon that we do eradicate.

Miller: But you have to catch them in time?

Ragozzino: We have to catch them in time and they have to have a way that we can catch them all. In the case of the Japanese beetle, which is one of our larger eradication programs, Japanese beetle larvae have to feed on turfgrass. So we have a weak point that we can target turfgrass and we know that if we hit all the turfgrass where Japanese beetles are, we can actually eradicate it. As opposed to something like brown marmorated stink bugs where it can feed on hundreds of different plants, there is no place there where we could actually feasibly eradicate it.

Miller: I can imagine some home gardeners listening right now, who are sick of these stink bugs and assuming, as you noted, that there’s a good chance that the bugs are seeing the invasive kind, might be saying, “hey, I want some Samurai wasps of my own.” Can people get these non-native wasps for home use?

Ragozzino: Not right now. Right now in Oregon, the only people who are mastering these are us and Oregon State University Extension Service for agriculture. So if you’re a grower who has brown marmorated stink bug damage, please reach out. We can do a site evaluation to make sure that these Samurai wasps can survive. Their best chance of surviving comes from when we take a look at a couple of different circumstances. But we want to release them at places where there are going to be heavy brown marmorated stink bug populations like adjacent to agriculture as opposed to home use. But homeowners and home gardeners will eventually see the benefits of this as the Samurai wasps move on their own to those areas where there’s fewer stink bugs, but maybe a little higher density in your garden

Miller: Max Ragozzino, thanks very much.

Ragozzino: Thank you so much for having me.

Miller: Max Raggozzino is a biocontrol entomologist with the Oregon Department of Agriculture.

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