When Insects Take Care of the Pest Control For Us

Episode 12:  When insects take care of the pest control for us https://www.mnipm.umn.edu//sites/mnipm.umn.edu/files/when_insects_take_care_of_pest_control.mp3

Show Notes

Episode 12:  When insects take care of the pest control for us

What is UMN Extension Field Crop IPM Podcasts?

Hosts Anthony Hanson, Dave Nicholai, and Bill Hutchison at the University of Minnesota alert growers, ag professionals and educators about emerging pest concerns with Minnesota Field Crops, including corn, soybean, small grains and alfalfa. They offer useful, research-based pest management solutions.

Dr. Anthony Hanson, IPM Educator - Field Crops
Dr. Bill Hutchison, Coordinator of the MN IPM Program
Dave Nicolai, Crops Extension Educator & Coordinator of the Extension Institute for Ag Professionals

Anthony Hanson: 00:06

Good morning. I'm Anthony Hanson hosting the sixth episode of twenty nineteen University of Minnesota IPM podcast series. Today, have George Heimbold with people in his lab, Jonathan Dreigny and Carl Steinhorn. So George, do you wanna introduce yourself a little bit, give a little background on who you are, and then also the other folks in your lab here?

George Heimpel: 00:25

Thank you very much Anthony for hosting this and for having us here to talk about the work that we're doing in our lab. My name is George Heimpel and I'm on the Mentomology faculty here at the U. My sort of role here is to work on biocontrol of various insect pests and I have a couple of people here with me as you mentioned Carl Svenoyan who is a postdoc here at the U, got his PhD here a couple of years ago, is here with us. He's been doing some great work and Jonathan Bregney has been sort of my right hand man for the last eight or ten years on the project that we're going talk about here and others as well.

Anthony Hanson: 01:07

So you mentioned biocontrol. So what is biological control compared to what we often know about using insecticides? That's one part of IPM, but that's only one branch. Biological control is another pretty important one,

George Heimpel: 01:20

right? Yeah, so biocontrol or biological control is basically using the good bugs to fight the bad bugs. And it could be bad bugs, there could be weeds. But as we know, nature is very diverse and there are a lot of interactions in nature and some of those happen to be certain animals, in this case insects that naturally feed on pests or invasive species. And so the discipline of biocontrol is one where we try to understand these interactions and try to harness beneficial insects to control pests.

Anthony Hanson: 02:03

So there's certain groups of insects rather that can be beneficial. You can have some that just eat the insects outright. I know there's some others parasitoids called that are kind of unique in that sense.

George Heimpel: 02:14

Right. So we typically would classify biocontrol agents into predatory insects and parasitic insects. And the predatory insects are like you say, they just eat other insects. They could include things like lady beetles. But then there are parasitic insects, which include the parasitic wasps or parasitoids.

George Heimpel: 02:37

And these are fascinating creatures. What they do is that they lay their eggs within or on other insects and those eggs hatch, turn into larvae, which feed on that host, which is then the pest, killing it in the process. Parasitic wasps are a huge group so there are thousands and thousands of species, almost all insect species have multiple species of parasitic wasps that attack them. So there's ample opportunity for us to find and study these parasitic wasps and to figure out how well they might be able to control our pests.

Anthony Hanson: 03:21

So your labs worked a lot on soybean and parasitic wasps in that group, as well as some other crops too. But this new parasitoid Aflinus cervicis kind of hit the news a little bit in the last few years. What's been happening with that in soybean?

George Heimpel: 03:36

Yeah, so going back a little bit, one thing that we found with soybean aphid was it when it invaded from Asia back in the year 2000, it really didn't bring with it any of those natural enemies that control it back in China. And the main natural enemies that control it in China are these parasitic wasps. So they were sort of a whole effort put into trying to find those and to try to bring over ones that would be ecologically safe to release, and that's a whole story in itself. This species that you're mentioning, Aphae line assertus is also from Asia, so it also coevolved with soybean aphid, but it came over by itself. We didn't bring it.

George Heimpel: 04:21

It just came over we're not sure how and it was first found in Minnesota in 2011 by our lab group I think Jonathan was there on that day and it's now eight years later one of the dominant natural enemies of soybean aphid, one of the species that's doing the best job in keeping numbers of soybean aphid far below what they would otherwise be.

Anthony Hanson: 04:45

Do you know of any numbers you might find in the field? So say for instance, I'm out there, how do I know this parasitoid is out there? Oh, yeah. And then how much of reduction might you see in soybean a for two? Gotcha.

Anthony Hanson: 04:57

Because of that.

George Heimpel: 04:58

Well, it actually is pretty easy to see in the field, even though they're tiny little wasps, know I should I should maybe emphasize that we call them wasps or parasitic wasps, but they're nothing like a yellow jacket wasp, they're really tiny, they're literally about the size of a printed period on a page. So they're really tiny, they pose no risk to humans or to animals other than aphids. But even though they're tiny, we can see them in the field pretty easily because when they sting an aphid, as they're killing it, they turn that aphid black. And what you see on your soybean leaf is rather than a plump green aphid, you see a little black shiny bullet shaped thing that we call a parasitoid mummy. So if you're a farmer or if you are a pest control specialist looking at soy leaves, you can see these little black mummies and then you'll know that you have this little wasp that's attacking and killing aphids.

George Heimpel: 06:07

And as far as your question in terms of what kind of benefit that they're providing, from the work that we've done over the last years, we've found that they're able to reduce the population of aphids below the economic threshold in something like 10% of fields. So what that means is that if farmers are using the two fifty AFib per plant threshold, then there'll be a 10% reduction in spraying statewide. Is the parasitoid widespread enough to where you might have a situation where a grower has to spray, but is it maybe slowing it down where maybe it may not be until later in the year or other areas maybe further down south where you maybe only have to spray once instead of twice? We have found it throughout the soybean growing area in the state. Actually Jonathan is the one that did some of that.

George Heimpel: 07:05

But yes, we have found it throughout the state and we also find it from early in the season throughout the whole season. So I do think it makes sense that it would delay the timing of the soybean aphid outbreak. So it could certainly push the outbreaks back into that sort of August timeframe when some growers might not even need to spray at all. And it could certainly also sort of slow the spread as soybean aphids are moving through not only the state but the whole soybean growing area. Did you want to mention something about your sampling, John?

Jonathan Dregni: 07:45

Well, can report the sampling for this summer we've had in Minnesota and throughout the 12 state North Central Region from Ohio to North Dakota and down to Missouri, very low aphid numbers generally. However, in Eastern Minnesota, Central Eastern Minnesota, we did find high aphid numbers, which is kind of interesting. But we've been doing a survey of many counties in Minnesota and across the North Central Region. And while we found very low aphid numbers, we do generally find Aphelinus even at very low populations. And so this parasitoid wasp, we do find in low aphid numbers.

Jonathan Dregni: 08:23

So the thought is that it is very closely following tracking the aphid to the fields in the springtime. One of the challenges that we have is understanding and trying to figure out what sort of management techniques might improve the effectiveness of this biocontrol agent.

Anthony Hanson: 08:41

So how many years have you been finding the wassail in the fields? Has it been just slowly building up? Or did you suddenly find it widespread, even multiple years? Or was it pretty recent that we really started seeing these high numbers?

Jonathan Dregni: 08:54

When I started working with the lab in 2008, we were still in the process of doing the host range testing. So these parasitoid wasps which we brought from Asia, we brought into a quarantine lab and were very cautious in handling them for many years. So that was my job was to handle those colonies and do some of those tests in quarantine here. We, in the year 2012, I believe it was, we had a major infestation of A. Folina certus, this parasitoid which arrived on its own to North America.

Jonathan Dregni: 09:23

So from that point on, we've been finding it basically everywhere that you find soybean aphid. It did take a while to get to Southeastern Minnesota, which is kind of an interesting pocket. But, Northwestern Minnesota has been, North Dakota as well, have been sort of central areas where we first find the Aphalinus certus in the spring and where we find the largest numbers. Minnesota is sort of the center of this question.

Anthony Hanson: 09:48

So Jonathan, you mentioned how we're finding the parasitoids with the Aemis pretty early on the season. How does that seasonality affect in terms of whether a parasitoid will work well with a given species? George mentioned we also have Carl here as well who's worked on overwintering, that seems like an area where can these aphids survive the winter well and are there areas related to that?

Speaker 4: 10:11

Yeah, so George mentioned this being a thorny question and I would agree potentially even a buckthorny question. This overwintering potential is pretty important because when you're importing an organism or if it shows up on its own, it's only gonna establish and be successful if the environmental conditions are appropriate

Anthony Hanson: 10:37

to,

Speaker 4: 10:37

that from which it came. So in some cases, we've seen biological control agents fail because of their inability to overwinter in a new habitat. Perhaps because they weren't adapted to that type of winter environment in the first place or because time spent in a laboratory while testing them resulted in evolutionary changes that led to them losing the ability to properly spend the winter. So we know that overwintering is important and when we're thinking about this parasitic wasp, A. Colina certis, some of the main questions are where is it overwintering and to what extent is it successful?

Speaker 4: 11:19

On the where front, we know that soybean aphid has a primary host or an overwintering host, which is buckthorn, another favorite invasive species of people in Minnesota and the Upper Midwest. So the question is, are aphelinus certus spending the winter in soybean fields after harvest just being laid down on the surface of the field and spending the winter there, or are they following these aphids into buckthorn patches continuing to parasitize them there while the aphids go through another generation or two and then coming back from the buckthorn to find the soybean aphids in the soy again in the springtime after planting. On top of that type of where question, there's also that micro habitat question. So we've done some experiments where we place these mummies out in the field, they're ready for winter. And then we either place them on the surface of the field or, on on the ground in buckthorn plots or on the twigs of buckthorn plots.

Speaker 4: 12:17

And then we come back in the spring, collect these mummies, and see how well they survive in these different micro habitats as we call them. And it turns out that a lot of insects and other animals spend the winter underneath the snow. The snow really acts as a blanket insulating any organisms underneath the snow near the ground at much more stable and oftentimes warmer temperatures in the air. And so this seems like an important consideration when thinking about where these insects might spend the winter. Are they capable of surviving the harsh fluctuating cold temperatures that would happen if they stay up on the buckthorn twigs?

Speaker 4: 12:56

Or are they landing on the surface of fields or in the woods and then being blanketed by snow and being protected that way.

Anthony Hanson: 13:03

So you mentioned how there might be some mismatch where certain insects may not be able to survive winters. So this isn't the first parasitoid for soybean aphid that's been considered here in Minnesota, is it?

George Heimpel: 13:15

Yes, so Anthony I think you're alluding to a few species that we brought in from Asia into our quarantine lab and did a bunch of studies on those which are basically aimed at trying to determine how specialized these parasitic wasps are. So let me just talk a little bit about the fascinating sort of life cycle of these insects. What they do is that they have a specialized egg laying organ, an ovipositor and they sting the aphid and lay an egg into the body of that aphid. And then that egg sits there for a day or two and then it hatches and then you have the larva that's kind of swimming around within the aphid blood or as we call it the hemolymph. And so it goes through this larval stage takes a few days and then it goes to the pupil stage as I said it turns the aphid into this sort of leathery husk that we call a mummy and then after about another week it pops out as you know an adult wasp and is ready to start the cycle again once it mapes.

George Heimpel: 14:26

So the question is for a given bio control agent when we bring it into quarantine and try to determine whether it would be ecologically safe to release it, can it parasitize a lot of different species of aphids or other insects or just the soybean aphid and maybe maybe a few more. And so that's what we spent years doing with a total of about 20 different species of parasitic wasps and we actually found that most of them were able to attack a lot of different aphid species, which maybe to some people doesn't sound bad if it attacks other aphid species, but we have to realize that there are also native aphid species here that live in natural habitats. And we actually don't want these parasitic wasps to sort of infiltrate native ecosystems and have possibly unforeseen ecological effects there. Also, even if we didn't care about that, the federal government would not let us release a species of parasitic wasp that attacks many aphids species. Anyway, so we did these studies within our quarantine lab and in case our listeners don't know, we have at the University of Minnesota one of the very few such quarantine labs in the country.

George Heimpel: 15:51

So it really gives us the opportunity to do these studies in-depth. After all of that work, we came up with, there were three species of wasps which showed high level of specificity meaning that they should be ecologically safe to release. One of them the name was Binaudoxus communis and we had we ended up getting a permit to release that one back in 2007. And then another one was A.phalanus glycinus and then a third one was A.phalanus ramini. So we have a permit to release these three species and we have tried to release two of them and they did not establish.

George Heimpel: 16:38

And so that brings up a lot of questions. Some of those questions Carl has already mentioned, but why did they not establish? I'll tell you one reason that was not, that did not explain it and that's the effort because we released tens of thousands of these at various sites, actually more like hundreds of thousands. So the effort was there but they did not establish one of the theories for why they didn't has to do with this overwintering piece that Carr was just talking about. And it is certainly true that when you're holding an insect under lab conditions for many years, things can happen.

George Heimpel: 17:31

The evolution of traits that favor living in the lab, which is sort of a super cushy environment where you don't have a cold period, you don't really have to search for hosts, there's a lot of things that can change when you put an insect into a lab setting for many generations. So there could have been basically the genetic erosion of some of these important traits like the ability to overwinter, the ability to find hosts well, the ability to fly well. There's a lot of those things that could have eroded in the lab. And this is unfortunately a trade off of sort of modern biocontrol. So modern biocontrol is very safe.

George Heimpel: 18:16

So as I mentioned, we're very focused on not releasing something that's going to cause either ecological harm or economic harm or any kind of harm because that's what we've learned over the years, it's something that we really have to guard against. So we're doing great on that front and we need to do that, but it does come at a cost and that cost can be that you need to keep these insects in culture for many years. In doing that, you might get the genetic erosion of important traits. So I think this is maybe going beyond the question you have, but I think a sort of frontier in the science of biological control is how do we deal with this? And there various methods that can be used to overcome this.

George Heimpel: 19:10

But that's sort of something that the biocontrol community is grappling with now. To make a long story short, we have released two species and they fail to establish. Those are both released basically, one was before A.phalinus cervis, one was just as A.phalinus cervis was starting to come into play. The third species we could still release it, we've been doing overwintering studies on it and it seems to not be able to overwinter as well as the others. And also we have A.

George Heimpel: 19:44

Feline assertus now, so it's not as clear that an additional species like that would really help a lot. But anyway, that one is still in play.

Anthony Hanson: 19:54

So a lot of your lab's work has been based in soybean, but what other crops that could benefit from biological control in

George Heimpel: 20:00

As far as the crops that benefit from bio control in Minnesota, I would say I would probably talk about alfalfa first. And there are two major pests of alfalfa that are being brought under bio control and the first is alfalfa weevil, which I guess it's kind of rearing its head again now. It was a really bad pest going back to the 70s. And in the 1980s, you started to have people bringing in various species of parasitic wasps. There were at least three species, three major species that were brought in.

George Heimpel: 20:38

And they, you know, one of them was especially important, brought that pest under complete biocontrol to the extent where, you know, a lot of growers from the 80s and on through the 90s and the early 2000s didn't really ever see alfalfa weeble. I think as we were mentioning off mic earlier, there is sort of the specter of the reemergence of that pest so that will be interesting to study. But there's also another pest of an alfalfa that was brought under BioControl and that's the alfalfa blotch leaf miner. And it may be that some of your listeners might not even know this pest, it's the same kind of thing where two parasitic wasp species were brought into control, this was in the late 1990s and brought it under complete biocontrol too. So you know the alfalfa bush leaf miner and the alfalfa weevil were two pests that at a certain point were causing a lot of damage causing farmers to have to spray.

George Heimpel: 21:45

For the alfalfa weevil there were decades of no problem at all, so saving a lot of need to spray. And it's the same for the blush leaf liner.

Anthony Hanson: 21:56

So for just kind of a wrap up question though, we talk about parasitoids a lot, all spreaders, but how do they fit into integrated pest management in general? Biocontrol is essentially kind of a free pest control in a way we have our other tactics too and insecticides come up a lot. How do those interplay whether things to watch out for or when it can be beneficial? We talked a little bit about how we can delay insecticide treatments if need be, but what's the other end and how the other tactics affect these biological control agents?

George Heimpel: 22:25

Well, I think that's a great question, Anthony. And different people talk about IPM in different ways, but I think of it as sort of a three legged stool. And one of those legs is pesticide use, certainly, and another leg is plant resistance. And the third leg is bio control. And they all affect each other in interesting ways.

George Heimpel: 22:52

So you mentioned the effect of bio control on insecticide use. Certainly bio control can lead to lessened insecticide use, but in order for that happen it's really good to have a threshold that is used by farmers so that they don't just spray early in the season or on a schedule. If you have a threshold then it allows biocontrol to lead to less spraying in an organised way. By the same token, insecticides have an influence on biocontrol and that influence is to disrupt it. And so you know it's important to know and it makes a lot of sense that you can get better biocontrol by spraying less or by spraying only in certain areas.

George Heimpel: 23:44

So that's another way that they interact. These things also interact with host plant resistance and often host plant resistance and biocontrol can kind of work together as a team. And we've actually done work on that for the soybean aphid system and found that to be the case because often host plant resistance can bring the pest levels down to a level at which biocontrol can further knock them back. And typically host plant resistance doesn't have a negative effect on the biocontrol agents in the same way that pesticide use does. So I think we have to recognize that biocontrol is an important part of the IPM trifecta and we have to understand how it interacts with those other legs of the IPM stool.

George Heimpel: 24:42

Is really an important part of how our pests are controlled naturally.

Anthony Hanson: 24:48

Well, you, Doctor. Heimpel and the rest of your lab for stopping in today. We'll meet up with everyone else most likely next year. This will probably be our last episode for this year of the IPM podcast series. Thank you.

George Heimpel: 24:59

It's been a pleasure. Thank you.