Researching Aphid Outbreaks on the Palouse with Dr. Rob Clark

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Episode Transcription:

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Drew Lyon: Hello. Welcome to the WSU Wheat Beat podcast. I’m your host, Drew Lyon, and I want to thank you for joining me as we explore the world of small grains production and research at Washington State University. In each episode, I speak with researchers WSU and the USDA-ARS to provide you with insights into the latest research on wheat and barley production. If you enjoy the WSU Wheat Beat podcast do us a favor and subscribe on iTunes or your favorite podcasting app and leave us a review while you’re there so others can find the show too.

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Drew Lyon: My guest today is Dr. Rob Clark. Dr. Clark is a Postdoctoral Researcher in the Department of Entomology at Washington State University. He’s working with Professor Dave Crowder. Rob is currently working on a USDA funded project that aims to better understand pest insects and diseases in cultivated legumes of the Palouse. As an insect ecologist, Rob has worked on a range of insect species important to forest and agriculture, in both New England and the Pacific Northwest. Hello Rob.

Dr. Rob Clark: Hi.

Drew Lyon: Please tell us a little bit about your area of research here at Washington State University.

Dr. Rob Clark: Yeah sure. By training, I’m in insect ecologist. And I really want to understand what causes outbreaks of insect pests. In some years or locations insect herbivores, whether it’s aphids, or beetles, or caterpillars, will have really dramatic outbreaks. But other conditions, they don’t really seem to outbreak at all. Why is that? It’s a really good basic science question, I think. But it’s also one really relevant to agriculture, because predicting outbreaks is a really important component of effective pest control. I try to look at the big picture as an ecologist, and try to understand what impacts these populations; and for me, that’s for looking at things through the lens of food webs. There are many reasons insect herbivores can outbreak. But their two most general causes are an abundance of food resources, which ecologist’s call a bottom-up effects, and/or lack of predators, which ecologist call a top-down effects. So think things like plants that are susceptible to herbivores would be something that provides a lot of food to herbivores and allows an outbreak, or a lack of natural enemies, if there’s no biological control, you could have insect outbreaks as well. So that’s a general framework I have as an ecologist and how I hope to approach applied insect problems in agricultural systems.

Drew Lyon: I know as a weed scientist, you know, weeds tended to be with us in most years. But I’ve noticed that about insects; you’ll go years without any problem, and then all the sudden, you just get hammered with them.

Dr. Rob Clark: Yeah.

Drew Lyon: That’s very interesting, and if we could understand that, that would be very helpful. What kind of agricultural insects are you looking at specifically?

Dr. Rob Clark: My past work has been on caterpillars, actually, in forest ecosystems. And I’ve changed gears a lot, and now I’m working on pea aphids in cultivated legumes in the Palouse. They’re really fascinating an insect to work with. They have this really high population growth, and they have this one-two punch where they will outbreak, and that they can transmit a whole mélange of pathogens to plants they’re feeding on. Aphids, while they’re feeding can transmit things like viruses to their plans, and this actually can do more damage than the feeding itself. The pathogen we’re looking at right now is a model system. It is Pea Enation Mosaic Virus, or PEMV for short. And it has had some significant outbreaks in the past in the Palouse, and it caused a lot of yield losses. But then in other years, it really hasn’t been much of an issue at all. So that gets to sort of my key question as an ecologist, to understand why that is the case.

Drew Lyon: So how do you go about studying aphid outbreaks in the Palouse?

Dr. Rob Clark: That’s a great question. So a lot of research has examined how biological control agents can prevent population growth of aphids. And more research still is gone into determining what crop varieties, or species, are susceptible to them. I’m trying to build on this work to help us make, you know, better predicted models for herbivores to see when these outbreak might occur. The research I’m doing this summer and the past summer, we’re currently monitoring aphid populations in a range of habitats in the Palouse, and then also along the Snake River. Pea aphids that attack cultivated legumes, especially dried pea, are found on other plant species that are not cultivated like dry pea; things like hairy vetch, which is a weed along the Snake River Valley. It’s also used as a cover crop, it’s used as cattle forage. It’s a pretty abundant plant. And it is a really great host plant for pea aphids, unfortunately. So as I said earlier, a fundamental question in entomology is understanding how outbreaks start. And I think our observation that hairy vetch is abundant, and that aphids can also feed on it, is really important to understanding the patterns of outbreaks. Pea aphids, believe it or not, actually colonize the Palouse from populations that are overwintering as far west as Corvallis, Oregon. And that’s generally where we thought, up until now, where the pea aphids come from, essentially. However, I think that this hairy vetch population is playing an important role in their dynamics, within a given season. So we’re closely tracking populations of pea aphids this year on vetch, and then also tracking population on dried pea that are along the Snake River.

Drew Lyon: Okay. Are you finding evidence that the pathogens move directly from vetch into peas?

Dr. Rob Clark: Yeah, so that was one of the first things we wanted to test, is we see pea aphids feeding on vetch in large numbers, and then we see, you know, pea aphids are one of the most pest to dried pea along the river. So the first thing we did is collected some plant tissue and tested them for legume pathogens. And we found that hairy vetch has a lot of pea enation mosaic virus, this one virus we’re studying a lot. So that’s really-that was really exciting to me as an ecologist, but also raises some flags that this host plant is actually potentially really important reservoir for some for some crop pathogens. So we’ve been able to demonstrate this in greenhouse experiments. If you grow a pea plant right next to a vetch plant, and put infective aphids, so aphids that can transmit the pathogen on vetch, and then watch the aphids move over to pea, they can transmit it. So it’s a simple experiment, but it’s really important thing to demonstrate that vetch can actually have the virus replicate in its tissue, and then aphids can feed on one and move it to another. So that’s kind of the smoking gun we were looking for. But when we did field trials, it didn’t look like vetch was any better or worse at transmitting the pathogens then pea plants themselves. So one of the things we really wanted to figure out was; well, if you have weedy vetch coming up in your field, should you be concerned that it’ll increase the rate of transmission of pathogens and attack crops? Doesn’t seem to be the case. Where we’re going now, is we’re thinking this happens at a landscape scale. So you have these really large populations of vetch in canyons, aphid outbreaks occur there, and then they ride wind currents up to the Palouse. So we have greenhouse evidence and then some landscape scale data we’re following up on now.

Drew Lyon: Okay. So you’re finding that it’s mostly along the river, where this vetch grows, but as you mentioned, I think earlier, vetch is also a component in some cover crops.

Dr. Rob Clark: Yes.

Drew Lyon: And as these cover crops get going, that might be of concern as well. So how can the movement of aphids between cultivated plants, your peas and weeds, such as vetch, be important to the control of this pest and the pathogens they carry?

Dr. Rob Clark: Yeah, so we’re still active in this research, so we haven’t come up with, you know, management decisions yet. But I think the current framework we have is it would be really useful to use vetch, actually, as an early warning system. So if you-it’s much warmer in there-in these lower areas, canyons along the Snake River and other places. So the vetch are coming out a month or two before the pea plants are even big enough for aphids to feed on them. So if we see these viruses building up in those plant populations, or aphids building up quickly, it might help us predict that there’s going to be an outbreak year for aphids. And I think that’s the best use of this information. Because a lot of the places I’m collecting these pathogens are sort of like roadside edges, ditches, sort of like disturbed environments that aren’t managed in any way, is where these outbreaks kind of look like they’re starting.

Drew Lyon: Okay. So I could envision something where these areas are being monitored, and you have some kind of website or place growers could go to see whether this is going to be predicted to be a bad pea aphid year, or not?

Dr. Rob Clark: Yeah that’s definitely what we’re doing this year, and I’m very excited about that, because we have a bunch of traps set up, normally in pea fields, all throughout the Palouse, and now we’ve added some to these vetch populations. And I think it’ll be very useful. And that’s going to be actually put on the website. Definitely our pan traps that are along the Snake River Valley are going to be added to that in pea fields.

Drew Lyon: In addition to peas, do we see this aphid on other legumes, because we grow chickpeas, we grow lentils, now we’re introducing fall-sown peas. Is this a pest on some of those other legumes? Or pretty much just on the dried pea?

Dr. Rob Clark: Yeah that’s a really great question. So dried peas are definitely what we’re focusing on. It doesn’t seem like pea aphids can transmit this pathogen to like garbanzo, for example. But really not much work has been done on it. So we’re hoping to look more into garbanzo. And the other thing I wanted to note that’s important, is that hairy vetch is not the only weedy legume that occurs in the Palouse. There are lots of other species that have escaped cultivation or are exotic weeds. And the thing that’s kind of good to know, is stuff like clover, sweet clover, hop clovers, because anything that call the clover so far that we’ve tested, is really not a competent host for pathogens that attack cultivated legumes. And in fact, they’re actually really poor hosts for pea aphids too.

Drew Lyon: That’s good news.

Dr. Rob Clark: So we’re hoping to follow up on that. Then maybe there’s some cover crops that would be better for controlling pea aphid populations at a regional scale.

Drew Lyon: If our listeners are interested in some of this work, is there a place they can go to find more information, like a website, or do you put out an annual report on what you’re doing?

Dr. Rob Clark: Yeah, so right now, as I mentioned, my work is being contributed to the website, hosted by University of Idaho. But this is all very new work. I’ve been here for a year and a half, and we’re just getting this project started. And I think it’s going to be-it’s going to expand to include more than pea aphids, things like pea weevil and wireworms use other host plants in this area, we don’t really know much about what host plant they could use. So I’m interested to hear from growers and, you know, what are some of the up-and-coming pests in legumes and wheat that we really struggle to predict their outbreaks and it’s difficult to control them for that reason. So I think we’re also going to post my email on here, as well.

Drew Lyon: We’ll make sure your email gets into our show notes. And the website you mentioned earlier at Idaho, could you tell us that website address. Do you know the URL?

Dr. Rob Clark: Oh yeah, it’s

Drew Lyon: All right, very good. Well Rob, I appreciate you coming in and talking to us about your research. It sounds like it could really expand to cover quite an area. And you’re going to be very busy. And we’ll look forward to seeing what you discover in the coming years.

Dr. Rob Clark: Thank you.

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Drew Lyon: Thanks for joining us and listening to the WSU Wheat Beat podcast. If you like what you hear don’t forget to subscribe and leave a review on iTunes or your favorite podcasting app. If you have questions or topics, you’d like to hear on future episodes please email me at drew.lyon — that’s –( You can find us online at and on Facebook and Twitter @WSUSmallGrains. The WSU Wheat Beat podcast is a production of CAHNRS Communications and the College of Agricultural, Human and Natural Resource Sciences at Washington State University. I’m Drew Lyon, we’ll see you next time.

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