Al & Juddy enjoyed having Stephen Goldson from AgResearch in the studio as their second guest.
Stephen shares his intrepid journey on controlling the Argentine stem weevil population by retrieving parasitoids from South America and bringing them to New Zealand.
Tune in for a first hand account of ecology in action.
"In terms of Conservation Biocontrol, we cannot use examples of this approach from abroad. What we can do is import biocontrol control agents that have evolved in association with stem weevil through evolutionary time, which is what the importation biocontrol is all about." – Stephen Goldson
Allister Here we are with Lara from marketing with some new questions for us.
Lara Yes, everyone was quite keen, had quite a few questions pop through, so it's really cool to see. First up, we have one from David Squibb.
Allister Squibby is a previous colleague from us in Tasmania. So we're excited to see the question.
Lara Can you please explain the nitrogen production cycle using legumes in a pasture system? And how do the nodules release N?
Allister Yes. So this is the natural relationship with legumes where they have a symbiotic relationship with a small fungus that creates nodules that absorb atmospheric nitrogen and provide the plant via these nodules with a source of nitrogen.
Glenn Because I think we forget that the air we breathe is about 70% nitrogen. There's a lot up there, and I guess the clover plant is just taking some of that and putting it into the ground.
Allister Correct but there's two ways that the nitrogen fixed in these nodules cycle. And you've probably got a stronger lead on the first way.
Glenn Yeah. And I wouldn't say it's the most important, but it's the coolest of the two. And that is where you've got essentially plant proteins in the clover plant that are being consumed by animals. And a proportion of those will then be returned to the soil through urine. And that is a really important way that we cycle nitrogen. So animals coming through the pasture are consuming that material. The nitrogen in that, some of it's used for productive purposes in the animal. But a proportion of that is also cleared in urine is returned to the pasture and becomes soil nitrogen.
Allister I'm suspicious that part of your question is associated with arable rotations and nodulation of legumes in arable rotations, where the primary mechanism for building soil available nitrogen for future cropping rotations is in the nodulation of the legume and the absorption of atmospheric nitrogen and then the breaking down of root material, including the nodules which get released on a warming soils. So what you're tending to find is you can grow legumes and they get nodulated they build up with nitrogen. And then as you go through the heat of summer or the colder winter, those nodules break off and the roots and root hairs die. And you tend to find they all get mineralised when soil temperatures are in the happy place for all the microbial activity to occur, which is pretty much the early to mid spring and early to mid autumn when all that gets released.
Glenn So actually the root death and the nodule breakdown is actually a naturally occurring process.
Allister Technically you would describe a spring flush and an autumn flush and most of that has been driven by microbial activity of breaking down roots and root material that has died through winter and died through summer. And they then get broken down in the following sort of 2 to 3 months when all that biological life really lights up. So Squibby I hope that helps. I do think it's really important to understand, though, that they typically an early to mid spring and early to mid autumn when all that nitrogen gets released apart from in your arable systems, when you actually work in those root structures after you've harvested legume based crops and you tend to find that builds up your soil nitrogen environment well, but you still tend to find the primary breakdown phase is in that sort of like in the early to mid autumn and early to mid spring.
Glenn So summary nitrogen out of the atmosphere into the plant goes into the soil in two ways, directly through root death or nodular break breakdown or indirectly through the animal out through urine into the soil.
Allister Yeah, cycling.
Lara Awesome, what a great explanation. Thanks guys. Another Q from Mark who likes to send through a few. How many liter’s of urine was tested in the development of Ecotain.
Allister Hmm. That's a question for you, Glenn.
Glenn That's a great question.
Allister And I would add another one on to that and what types of urine.
Glenn Yeah, well, I was going to say it would be easily into the thousands of litres of urine that we have collected, and measured.
Allister Oh man Glenn, you really take the piss.
Glenn And to the to the point that a lot of that's been done in with dairy and beef cattle and they're producing quite a large amount per day, so quite easily to fill up a 20 litre container quite quickly from dairy cattle. We have also done this in sheep. So a lot of work in sheep, not so much volume there. Deer, so again, not huge amount of volume, but we've been working in deer. And dogs, we've done a little bit of work in dogs and it's not really around urine volume, but certainly nitrogen concentration. They have very concentrated urine dogs. If you haven't A observed or B smelt dog urine.
Allister I do think it's ironic how proud you were when you showed me the first photo of a bucket full of deer urine. I thought that was really weird. Anyway, moving on.
Lara And one last one. If you were a forage, what would you be and why?
Allister You first Glenn.
Glenn Well, I've thought deeply about this obviously. And I reckon I'm probably the closest to Savvy cocksfoot. And the reason I say that is because it has got good, strong roots. From time to time, I do look a little bit scruffy. So similar there, I've some really clumpy habits, so very similar to a cocksfoot, and I am at home in Canterbury, which is very much like a cocksfoot. So I think a Savvy cocksfoot is probably what I'd be most aligned to.
Allister If well managed. You're quite palatable too, but if you left unmanaged, your palatability does go off a little bit Juddy.
Glenn Yeah that's right I need to be managed.
Allister Gosh, that's a hard one because, you know, I do quite like my plants and my different cultivars within the Agricom portfolio. I actually would just go for white clover. I think it's pretty plastic, I reckon I can be a bit plastic at times and change to my circumstances. It can be treated pretty rough there for a periods of time but if its lax it can actually turn into a completely different animal. I quite like that. Yeah I think white clover it seems a bit of a catch all one but I'd probably have the strongest affinity for white clover.
Glenn Do you reckon you'd be a small leaf clover or a ladino white clover.
Allister I suspect one of the listeners that might be related to me, might say I'd be a large leafed white clover. I think those listeners would fully appreciate that. Anyway.
Glenn Awesome. Thank you to you both. If you have any questions, technical, serious or anything and everything in between, please feel free to email firstname.lastname@example.org or flick us a message on our Facebook page agricomnz, thanks.
Glenn Hey Allister, you're looking good, nice top.
Allister Oh, thanks, Juddy.
Glenn I hope it comes back in style one day. What are we talking about today?
Glenn Well, it's my great pleasure to introduce Dr. Stephen Goldson. I'm really excited about having you here today, Stephen, because my overlap with the discussion today goes back to 1994 when I was a student and I presented a paper out of my masters at the Hamner Springs Grasslands Conference, and I believe that might have been your first grasslands paper at the time.
Stephen Yes, I think it was.
Allister Yeah. And that was just the introduction to the topic we're going to discuss today, which is the story behind the biocontrol of the Argentine steam weevil pest, New Zealand pasture pest by Parasitoid. So, Juddy, that's what's online today.
Glenn Great. Pleased to meet you, Stephen. Just a couple of questions to get to know you a bit. So tell me a little bit about, maybe your first job. What did you do as a job before you became an entomologist?
Stephen Strawberry picking.
Glenn Wow. And did you enjoy that?
Stephen Not really, no.
Glenn That's probably why you're an entomologist, excellent. And your first car, what was your first car?
Stephen Well, it was a Borgward if you've ever heard of it, made in East Germany.
Glenn Was it a good one?
Glenn All right. And then you moved on to something else. What was your second car?
Stephen An Austin, A55 which is slightly worse.
Allister That's classic.
Glenn Oh. I had in Austin and mine was probably not much better.
Allister We called it the pram, if I remember right back in university days.
Glenn Yeah because we were always pushing it. Any mentors? That you had early on that kind of shaped you.
Stephen Well, Dr. Peter Pottinger, well known to many people, was a big influence. And Bill Cain, the late Bill Cain was a great friend and mentor and Rod East and few others who sadly passed away. They were real mentors.
Glenn Because it strikes me entomology isn't sort of a glamorous career, you know, when you think about those things. But obviously, there are some really passionate people in that line of work.
Stephen So you don't think it's glamorous?
Allister And I think you're about to find out just how glamorous it is Glenn.
Glenn One final question is how much sleep do you work on? I have a theory about how much you sleep and your career choices. So how much sleep do you work on Steve?
Stephen 12 to 2 hours, depending on what's going on.
Glenn Right so quite variable.
Stephen And I never know when it's going to happen.
Allister And I think now would be a nice opportunity to just ask, you know, like what do you do Stephen? How would you describe your most recent part of your career and what are you doing today?
Stephen I'm working as emeritus at AgResearch as a principal scientist, I've got very interested in the work we're doing. Funding's not very available. I didn't want to keep grabbing the funding in my dosage. So I work now unpaid, but fortunately AgResearch has given me permission to use all the all the infrastructure there is. And I'm also working very closely with Otago University Biochem Department. So we're pushing ahead with the science.
Allister And in our right to say entomologist at heart and through training or ecologists.
Stephen Population ecologist, really, I'm a hopeless entomologist. I can't identify anything, actually.
Allister Yeah, but population ecology is actually still the heart and soul of some of the discussion today.
Stephen And so we get into population genetics through Peter at Otago University.
Allister Yeah and I think you know I've discussed this in passing but I look at the art of agronomy and some of it's just growing crops in some context around the world. But the way I look at agronomy is there's a really a strong ecological background and you're looking at soil plant, animal insect environment interactions and you have to see it all, which I think is a really, really positive lead into the discussion we're having today.
Glenn So we're going to talk today about Argentine steam weevil. Just gives a little bit of background to that particular insect.
Stephen Well, when I was at Otago, I said I wanted to be an entomologist who said, well, you can't do it here you've got to go somewhere else. Where and they said, Lincoln. I said, Well, where's that? You know? And I finished up with Peter Pottinger, who some of your older viewers may recall. And he did his master's on Argentine stem weevil. And he did two things. One, is he impressed on me that he'd done it all and that I should also work on it. And so, like saying, well, what do you want me to do? You've done it all. So he and I worked on stem weevil.
Allister How long ago was that.
Stephen Well, this is about 1974. I turned up to work with Peter Pottinger, who almost immediately left and went to MAF. So then I was left with others.
Allister And I think we should just clarify a couple of things is that, you know, in amongst the New Zealand pastoral system, you know, we're quite an island nation, very, very remote, and you're going to hear themes about our unique landscape over this podcast, I'm sure. But we have about three or four very, very big pasture pests associated with our introduced production systems, particularly in our grasslands and two natives that have successfully crossed into our farming landscape. But Argentine stem weevil, unless I am mistaken, came to New Zealand really quite early on in the history of New Zealand's farming development.
Stephen Recent work we've been doing with Alan Stewart and others, looking at very old seed samples, we've found bits of stem weevil in those seed samples. We deduced variously that it probably came in around 1900, if not before. And I think we think that that's something to do with trade with South America, which is obviously where the weevil came from.
Allister Called Argentine stem weevil.
Glenn I was going to say it does the name give it away a little bit.
Allister I think so Juddy.
Glenn So we've got this stem weevil lifecycle. Let's just give our listeners a feel for the life cycle.
Allister And what it does.
Stephen Well, its lifecycle is two and a half generations a year. Interestingly, it goes into something called dye pours, which is caused by shortening days. So it's a voter period and it goes into a kind of hibernation which it doesn't need to go into in New Zealand our climate is not such that it needs to do that, but it's what we call relic behaviour is what it evolved when it was in South America and it's still doing it. Its pest problem is caused by its grubs which develop in the stems of the grass. The weevil lays its eggs on the surface of the stems and in go the larvae. And in order to produce another stem weevil at least so 4 to 7 tillers are killed in the process of one generation. The thing about stem weevil here is we're finding we have found up to about 500 per square metre, that is adults, which is astonishing compared to what we see in South America. And it's that burden of a few things. Think each of those weevils has killed five tillers and it can just wipe out ryegrass.
Allister And in practice you know, in my history of practice in pastoral landscapes, I described that as a stem weevil storm where you can see feeding in different locations. But when you get these storm events, it's just complete annihilation.
Stephen Yeah, you don't get any recovery after it's rained. It looks like it's droughted and then you get autumnal rain and nothing happens. And that's classic stem weevil and it's quite uniformly distributed. So it's not like grass grub or something. It's pretty much across the whole.
Allister And that's really why the story today is so significant, because the next part of this discussion is that you're looking at strategies for managing such an important pasture pest in the New Zealand landscape. You know, our business invested in many years of endophyte technologies and endophyte is a natural fungus found in the ryegrass plant, which has the ability to manage Argentine stem weevil to a certain degree. But most of this is found in perennial ryegrass, so you've got annual ryegrass, biennial ryegrass and hybrids and many of these have different relationships with the fungal endophytes so not all fungal endophytes are fully effective against Argentine stem weevil and have different mechanisms for working on. So we've got this. But this story today is about the development of a biocontrol in this field. So really, I suppose delving into what are we talking about as far as a bio control for the sort.
Stephen Well, the first thing I would say is because the larval stages are in the stems, there's no chance at all of using pesticide. And besides, you can't really use pesticide on a broad acre basis anyway. The other problem with stem weevil of course, is it nips off the cotyledon of the emerging grasses. So you've got a real problem there with pasture establishment.
Allister Just to clarify, the adult weevil is a pest of a very, very newly emerged pastoral grasses. And so that's a pest, but it's the larvae that is the damaging event of an established pasture. And economically they're both probably about equal. But the pasture establishment phase has quite a dramatic collapse, particularly.
Glenn And I guess the question is that obviously there are some endophyte protection for some of our pastures with the right endophyte in them. But I guess what you're indicating, Allister, is that at establishment, the alkaloids that those endophytes are producing aren't high because we're in the establishment phase and we're dealing with an adult that's feeding and therefore endophyte while it protects against some of those larvae, for example, it's not protecting against those.
Allister It's about six weeks. And to be fair, the spread of seed treatment as we stand today is on the basis of protecting seedling plants as much as possible until the natural endophyte process kicks in.
Glenn So biological control of adults would be very useful if we had that.
Stephen Yeah, anything that reduces the population is what biocontrols about. The biocontrol is not complete control, as you know. It's about suppressing the weevil levels to a level where they cease to do a whole lot of damage because the plants are compensating for that damage. So the idea is to drive the population down and keep it down.
Glenn Just, I know there's probably more than one type of biological control. Can you tell us a little bit about that?
Stephen Well, as conservation biocontrol, where the idea is that you plant species which will, if you like, encourage natural enemies to establish in the pasture. There's importation biocontrol, which is what we're going to be talking about. And then there's a thing called inundated biocontrol usually in greenhouses and things where you release millions of things which are mass reared. The conservation biocontrol in New Zealand doesn't work very well because our forest areas have biocontrol agents in them, but they evolved to live in our forest areas. They have had nothing to do with the ryegrass clover and European plant species that we're using in New Zealand. So consequently they don't move into our grasslands, into our pastures in the way that they do in Europe. And so quite a lot of what we see about pest management impasses in Europe doesn't really apply here.
Glenn Which is a really important point because I guess what you're saying is we can't look abroad for the solution. It's actually going to be quite New Zealand specific.
Stephen Well, what we can't in terms of conservation biocontrol, we can't use examples from abroad. What we can do is the importation of biocontrol, which brings in specific natural enemies which have evolved and been associated with stem weevil through evolutionary time, which is what the importation biocontrols about.
Allister So the bigger point, you know, very unique landscape. We've got lots of biodiversity, but it's inherently evolved from what we have been in the past. Yeah we're being brought a very developed and a new grasslands to our country and our intensive temperate agricultural system. And so the reality is probably it is well worth touching on this point is that literally any introduced pest that comes to New Zealand has no natural enemies and it's quite a big deal.
Stephen So they're using the jargon, our grasslands don't have much biotic resistance, which means resistance of biological things to the invasive species. So species which are of trivial importance overseas, get here and they go nuts because they get into wall to wall, high quality forages. There's no brakes on their population build up, which is why we get these colossal numbers of species which never show up like that in the places they came from.
Allister Absolutely. And that creates that same discussion and the same potential outcomes from biocontrol.
Stephen So it's double sword. You know, New Zealand is relatively free of pests thanks to biosecurity measures and MPI and all that stuff. But when we do get pests we have a big problem with the few that we do get. There's a lot to be said for keeping them out of New Zealand because when they come in.
Allister Yeah, they just love the place like we do too. So no, but that I suppose, leads on to what are the parasitoids we've been looking at in New Zealand over the years and probably, you know, we are a success story which has got a little bit to be said for what we've just described about the environment is that we have a very distinctly different environment to the forage landscape we've created. We have understood that the border is the best place to protect our country from just any basic pest because when it arrives here, it doesn't come with its whole ecosystem, it comes by itself and you tend to find we have created a very nutritional landscape for virtually anything that does arrive. But the same can be said for the parasitoid’s and the success of them when they are introduced in New Zealand.
Stephen Yeah, well certainly the weevil pests in our pastures, we've got lucerne weevil, Argentine stem weevil and more recently clover root weevil. They're all weevils, they're all big problems in our pastures. They've been controlled by a tiny wasp called microtoners, and it's been highly successful. The microtoners work very successful. And the reason for that, we believe, is that the natural enemies, these microtoner species have been brought in without their own natural enemies. So they go gangbusters as well. So really they've been introduced into an ideal situation, plenty of hosts, no natural enemies. So they've reached colossal the very capable numbers in terms of suppressing these pests. The big challenge was two fold, that is finding them overseas and secondly, making sure they will behave and not attack and wipe out native species, native weevils.
Allister Which is a big part of your importation and isolation process, quarantine.
Glenn Allister, talking about all of these weevils I didn't actually realise the weevils we have got, and I wonder if an Argentine stem weevil and a plantain weevil, for example, were having a fight who do you think might win that one?
Allister Oh, really? I would say Argentine stem weevil. Yeah.
Glenn You'd say the Argentine stem weevil.
Glenn Probably makes the plantain weevil the lesser of two weevils. Ha.
Allister Haha. That's a shocker. But, yes.
Glenn Let's get back to collecting our parasitoid.
Allister Yeah. So, look, you know, I've travelled quite a bit to South America, and I've seen Argentine stem weevil in dairy pasture about 400 kilometres south of Santiago, right through to pretty much just south of Osorno. And the primary dairy sector of Chile. And the key there is, I mean it's only on the other side of the Andes from Argentina. So it doesn't surprise me that they're there. But that leads on to Steve. You know, you've obviously looked at the natural range in the natural locations of Argentine stem weevil as a starting point for looking for natural controls.
Stephen Yes, it was quite daunting to get off a plane and I don't know where I was. Brazil told to go and find the weevils. I mean, it was really there was a 1947 document put out by the Commonwealth Agricultural Bureau that there was some in a place called Bariloche. Very like Otago. I had a Ph.D. student who said there was some in the cereals in South Brazil. I probably turned up at the wrong time of the year. So the place was freezing cold, pissing with rain so my job was to see what there was. And, a number of things presented complication. One was I wasn't good at Spanish. Least of all Portuguese. And the other problem was I had to like, collect at night and see these countries were kind of nervous it was not long after the dictators and there was me at night with a long thing like the barrel of a gun with a net on the end being pulled up by police and others, and unable to explain what I was doing there. So we worked in Brazil, we worked in Uruguay, we worked in Argentina, we worked in Chile. We went to Osorno in all of these places we found the weevil, which was the big surprise because as far as we knew, there were really only known in Bariloche, this place in South.
Allister That's where it was published.
Stephen Yeah, that's 1947. And so I was really surprised to find the weevil so widespread and amazingly that some of them were parasitised. And what I had to do is when I collected the 100 or so at night is sort them out because there's a huge fauna of moths, caterpillars, and God knows what in these samples, which I was bringing back to the hotel room and then having to take the lid off and deal with what was erupting out of the box and try and find the weevils in the bottom. I don't it's this is not a hard luck story it was what it was like was lucky there was a balcony, so some of the stuff would fly out. But I used to spend the night with all kinds of things and fished the weevils out and then dissect them on a little microscope that I had. And it was just amazing to find the parasite in all of these places. It was incredibly exciting. The important thing about that was we collected from very different climate zones some places in south Brazil, which were almost tropical, right down to Patagonia, which is like, you know, Southland or something. Bariloche type places.
Allister Bariloche is pretty much Queenstown.
Stephen Yeah. And right in Chile and certainly around Temuco in those places, which is in the south, right up to the top to La Sirena, which is sort of again desert. And we collected a lot from those places. I dissected them and we established that the parasitoid was widespread. Then I went home because we didn't know what I was going to find. And I wrote a very elaborate report hoping somebody would go over. And I was sent back almost immediately, which was a privilege. It was a good thing to do. But then we had the technical issue of collecting these weevils and sending them back to New Zealand. They had to go into deep quarantine in case of a God knows what the foot and mouth was a big issue. Anyway, they had to be sent back such that they wouldn't freeze in the hole of the aircraft because the planes were flying over Antarctica at the time. And Peter Pottinger was able had a friend that worked for Aerolineas Argentinas, and we arranged for these specimens to come over in the drinks cabinet in first class. So they were packaged. I assure you they were just crawling around.
Allister They weren't in iceblocks ready to go into a drink?
Stephen And they arrived intact. And my colleagues, John Prophet, Neil Craig Phillips, started to rear them out and they were rearing them. I was there for about three months and I had never seen the parasitoid. What we used to do is collect the weevils and then rear the parasitoids out of the weevils. I need to explain the parasite lays its egg inside the weevils body and then inside the weevil the larvae of the parasite develop and then kill the weevil right. So all I'd seen is the parasite larvae inside the weevils bodies. So I got back to New Zealand, went into quarantine. It was a bit like seeing your first child being born. I saw the parasitoid. I've never seen it, you know.
Allister Just to describe. But technically, it's tiny, tiny little wasp with a little am I right to say a little orange ovipositor?
Stephen Yeah, they vary in colour, but they are about two, three millimetres long, maybe less. They flit around the place, they are very fragile, very small. We couldn't really work on the parasitoid itself. So we used to work on the parasitised weevils. But getting the things over and getting them into New Zealand and starting to rear them was quite a thing. In the end we reared over a million and released a million across New Zealand. We found they're only moving about three kilometres a year, so we hit on the bright idea of selling them.
Allister So that's a really big deal because it's actually sets the scene for a little bit of what is to come in the storyline. So again, once they've went through quarantine and you've all also I assume during that phase you were doing a lot of reviews on what other species that could be impacted by it if it was released. A lot of I assume a lot of basic work around existing insect species.
Stephen We spent 700,000 or a million testing this parasitoid this tiny thing on other weevils to see if it laid its eggs in other weevils New Zealand species, native species. And we found that it was pretty much stuck to its knitting. It was particularly enthusiastic about Argentine stem weevil and not very interested or interested at all in the native weevils.
Glenn Which must be really important when you are importing exotic species. This must be a really important aspect of biological control.
Stephen Yes, it is about conservation. The last thing we want to do is wipe out the last numbers of a rare New Zealand species. Also fearful of disease, particularly foot and mouth and other diseases because all sorts of rubbish was coming over, you know, we didn't know what we had. So that was a major part of the project was to get permission to start this.
Allister How many years did that sort of entail.
Stephen Well, it took a year to probably importation, a year to a year and a half. That includes finding it, bringing it in and proving that it was going to stick stem weevil.
Glenn Was that initial importation in the drinks cabinet up the front of the plane? Was that the one and only time that material came over?
Stephen When I was over there I was sending bunches over all the time to my colleagues. So we must have sent several boxes over. We had special boxes with labels all over them, as you would imagine. And so we continuously acquired them over three months or something like that. The important thing was that we kept the populations separate. So the ones we collected in South Brazil were in a different cage, if you like, from the ones we connected somewhere else. The important thing about these parasites is they reproduce without males, so they produced identical daughters. So we kept each line, each identical daughter line separate in order to maintain what we called diversity because we didn't know which were going to do well and which weren't.
Allister Because it's quite a big deal, really, because basically they're clones. And so obviously, the genetic diversity of clones is pretty well very, very narrow. So right from the start, your diversity within this population came from your collecting zones predominately because within a narrow zone being clonal, all that they would have very little diversity within a zone.
Stephen Was interesting. We don't know what diversity we have within the zones or between the zones, and we're only just finding that out now since we've got whole genome sequencing, we know that there was somewhat differences in their appearance. If you tried very hard and looked at the veins in the wings and all this sort of stuff. But the diversity is very much a part of what we were trying to do in order to cover the New Zealand ecosystems. And without going into too much detail, it was suggested we played and we got the ones from South Brazil and released them in Northlands and the ones from South Patagonia went to Otago and I said, no, we'll release equal numbers of all of them everywhere and we'll let nature decide through selection, which was the right thing to do. It was very laborious. We had 100 and I think in the end, maybe 130 separate lines or something. And we equally raised all of those lines and we released equal numbers of each of those lines in every place in New Zealand. This is where the science came into it.
Allister This is a really big part of what is about to become the most interesting part of the story. So coming back to the release phase, I did a wee stint at Dera Sarai and back in the day where we were collecting border controls for ragwort and a number of the other weed species back in the day and used to have to collect them and then send them off for releasing. Now you had a million of these tiny, tiny things, but I assume the release was actually the parasitised weevil.
Stephen Absolutely. So you couldn't really handle the parasitoid. It's so flighty.
Allister And so fragile.
Stephen Very fragile.
Allister So the big point here would be good for everyone to be aware of is that it only spread at about three kilometres a year and nature was going to take a very, very long time to achieve population across the whole landscape. So again, we were dropping, parachuting, literally. These populations into different remote areas and then it would still take three kilometres a year to start to populate the landscape. So we all sort of, as we head into this next part of the story, which is actually what's happened to Argentine stem weevil parasitoid New Zealand, we have sort of got to understand every region of our country is at a different stage of time from release and even within districts and regions there could be 3 to 5 years apart before the parasitoid population has really stabilised. Because what has become most interesting and this is all sat across my career as an agronomist, is watching the impact of the parasitoid on moderating the pasture damage associated with stem weevil. We still see the odd stem weevil storm as the parasitoid has taken time to catch up with the population and for example, a cold spring. But what we've seen in the last decade is more and more of these storm phases taking out our pastures. Both young pasture but also fully established pasture that haven't got effective endophytes in them. We are seeing more and more pasture persistence issues and that started to pretty much kick in around, in my opinion, probably about 2010 to 2012. I started seeing stem weevil again at these levels. So what was actually happening?
Stephen So a couple of things happened. We sold these without knowing if they're going to work, which is a leap of faith, and we put all the caveats around what it is biocontrol, we don't really know. Well, it showed up to 90% parasitism all over the place incredibly quickly within four years.
Allister Hugely successful and this goes back to the ecology, doesn't it? It goes back to the fact the wasp had no natural enemies. So it just had this lovely smorgasbord of stem weevil everywhere and no natural enemies.
Glenn So that tells me the reproductive rates should be relatively high. Just give me a feel for an adult laying eggs. You know, what is the reproductive rate? How long do the adults live?
Stephen So the guts of that is they lay about 40 eggs each or 60, somewhere around there. They live about three weeks. They're incredibly good at finding the weevils. And they don't attack the same weevil twice and they lay one egg in each weevil. They have some magic way of telling that this weevils parasitised and this one isn't. So they use their whole complement of eggs. Now, what's interesting in the native ecosystem, and I'll go back to that briefly in a minute. In the native ecosystem into Montane Valleys in South America is bugger all plants and bugger all weevils. So they have to work really hard to find the weevils. What happens here? They emerge and they find all the weevils they need in about three days and then they're empty. But that there were enough of the parasitoids effectively using their whole egg loads to get this massive build up in parasitism. I think within 18 months down here in the warm areas and a couple years in Christchurch.
Allister About two and a half to three life cycles in a year.
Glenn The fact there was so many weevils probably contributed to the fact that wasn't spreading very far.
Stephen Absolutely. And the parasitised weevils probably weren't flying as much as I remember, but certainly that's why we needed to give it a push along. But the weevil itself came from these into montane valleys. I have to say, I don't want to oversell my adventures in South America because the truth is I got most of the parasitoids off football pitches and hotel lawns. Because you couldn't find it in the native ecosystem because native ecosystems were so shambolic basically.
Allister Absolutely multi-species. So it's only target certain grass species.
Stephen So they're moving into cultivated areas. And I make no apology for that. We couldn't possibly find them in the tussocks.
Allister It wasn't a target species. It was the lolium species amongst the tussock landscape.
Stephen Yes, that's right. But the habitat itself is very species sparse, let alone numbers of weevils, maybe one per square metre, if you're lucky.
Allister Absolutely, classic. So we've got the weevil now. It's in the country, it's been cycling and I think this is the point is that the Argentine steam weevil started to become damaging again. So you know what has happened and what has been the unique story actually about this whole parasitised?
Stephen Well, I was in deep denial for a while. Covered in glory, having achieved this, to be told by Alice and Piper it wasn't working. So in the end, I thought, I better get in the tent so we did quite a lot of work, sequential work. Looking at all the sampling we've done between, say, 1992 to 2010, 2011, then we did a whole lot more sampling and there was no doubt that the parasitism levels were dropping fast. And we found that the parasitism levels were dropping very fast at Ruakura and the levels dropped from about 80% to 10%.
Allister Which is on the verge of a failure.
Stephen But this becomes a failure at 60% because it does depend.
Glenn So that's of the population of Argentine stem weevil only 60% are parasitised.
Allister That's the threshold.
Stephen Yeah. So really to get effective reduction in damage, if you kill half the population, it doesn't make any difference because the other half just does better. So you get this compensation, you know. So we thought, well, 60% is what we need to get control. We were running at 85, 90 or 80 at Ruakura and we're having similar down in Canterbury. And then when we went back, it was down to 40% at Ruakura and then it was down to 35 and then 10. And we went here to Canterbury and it was doing 75%, and it was down to 30. And we sampled and sampled and sampled, and there was no doubt that the control agent was ceasing to suppress Argentine stem weevil because the parasite levels were dropping in the field populations of the weevil.
Allister So again, very unusual and the story of biocontrol. So what was going on?
Stephen Well, I thought of resigning, but then I thought I should pull myself together and made a detailed investigation. My post doc and I worked on this and we discovered there was some effects of grass types. And we found that the rate of reduction in the short rotation grasses was less than in the perennial. Well, to cut a long story short, we discovered that the weevil was becoming least parasitised in the warmer areas and not making much difference in Otago. So that decline and parasitism seem to be related to the number of generations of the parasitoid in the warmer places. So Ruakura may have four or five generations. We got three here and two in Otago. We realised that the amount of pressure, amount of parasitism that had gone on in these places, that was relating to the degree to which parasitism was dropping. And we did a lot of experiments and the Ph.D. student did some work as well, Morgan Shields. And we found that almost certainly what had happened is the Parasitoid had selected weevils that were more invasive. So the Parasitoid couldn't evolve because it's pathogenic, so it's stuck in its groove. The weevils could evolve. And what happened is the pressure that the Parasitoid had put on the weevil population resulted in the surviving weevils being those that could best escape from the parasitoid. Yes, sneaky weevils. So we kind of cracked it. And then when we thought about it a bit more, we realised that the weevils that we collected in South America probably had a bit of evasive ability because of the pressures that it had been under in its native range. And what happened is we selected on that evasiveness in New Zealand to get a crop of resistant weevils to the parasitoid.
Allister And sort of population. You know, so the couple of linkages there, remembering that the Parasitoid only travelled at three kilometres a year as it expanded. So every region in New Zealand hit sort of like peak patriotism and its own unique time. And then after that, what you've got is when you hit a certain number of generations of selection against these weevils that are easily targeted and that let's just use the words sneaky ones are escaping constantly the generations about 30 to 40 generations.
Stephen We think it's about 15 years or 17 years, 30-35 generations this was a world first, this was an astonishing result. No one's ever seen selection for resistance by parasitoid on a pest before. And it got into science and all these past journals. And I hope to God we were right. But I think we were. And again you say well, why did it happen here? Well, New Zealand's not like most places because of the simplified ecosystem that this ecology is occurring in. So the none of the complexity that goes on in mature ecosystems was operating in the New Zealand pasture. So no wonder we got these anomalous results.
Allister Yeah, and I think that's the thing we've, we had this amazing success story based on the success of this parasitoid and it had a big benefit on maintaining persistent perennial pastures in New Zealand only for generational selection to move the singular by control organism away from its host. And I think this keeps coming back to the point New Zealand's only invested in biocontrol to a certain degree. We only literally had one bullet in the chamber as far as the control of the species goes. And the reality is there it wasn't a complex ecosystem. There was just a one pest one parasite. And we've literally moved away. And we actually when it comes to biocontrol, we actually have no Plan B either, do we, because the country hasn't necessarily invested in this area.
Glenn That was going to be my question. We've got to what a sneaky weevil can we find a sneaky a parasitoid?
Stephen We are funded. I'm working with Otago University. The first thing we need to do is understand the genetics of what the hell's going on. If we can understand the genetics, then we may be able to start to select for active parasitism to these parasitoids again. We certainly will know what traits will predispose a parasitoid to success. So the more we know about the behaviour and the genetic drivers, the more we know about what to look for. If we're going to sharpen the thing up again and we may be able to using non GE, adjust these parasites so that they become virulent again, this is deep science. It's difficult science. The other answer is we can always go back to get South America and get some more, but it might just bring back what we've already got.
Glenn And with that in mind, because you're genomics testing all these populations of clonal, basically a clonal parasitoid, it really does highlight that basic scientific principles that you use by using diverse regions of capture and maintaining those populations individually could yet still hold a small key to reach some of the easier reactions to the topic.
Stephen If we look at which pathogenic lines and from which areas they were collected that are doing best in the different zones in New Zealand, we can then look at those, interrogate those and see what traits have allowed that selective advantage. Now, this might not work, it might not happen. This is science. Yeah, but we've got to follow it up and we are following it up. Otago University is working with us a lot and we have got some money for researching what it is that makes an effective biocontrol agent. So it becomes a science rather than an art, which it has been in the past. So we'll keep at it.
Glenn Yeah, I guess one of the really interesting things and when we talk about these being clones, if there was the chance that we could get something that was sexual at reproducing so that those genetics could follow the weevils. Is there an issue with that?
Stephen Yeah, there is. And that is we couldn't find any.
Allister That's a starting point.
Stephen And the other, the other issue is yes, they could, they could co-evolved. Another issue is we don't know what their survival rate would be either, because if you've got a new population establishing and that's actually reproducing and you release a few of them, they can't find each other. So they fizzle out. So the rate of spread of a sexually reproducing species is probably pretty bloody slow because it's been most of the time trying to find mates, so they go extinct. So that's the other problem.
Glenn We don't we don't ever a tinder for insects at the moment.
Stephen We're not working on that. We are we working on pheromones.
Allister No, but at least I understand though there is another complex situation and that a lot of these parasitic wasps of the species that are subtly different for the different weevils that they are targeting can actually cross. And unless I'm mistaken, that's another problem with the more sexually diverse and the more genotype diverse styles is that if you suddenly get two groups crossing, you may actually de-power, both of them from their target species.
Stephen So you've got sexually reproducing strains and strain differences make a big difference in terms of host range and efficacy, and you bring two separate strains in for it before one crop or another and they hybridise. There's a good chance they won't be any good. So great care has to be taken because if you hybridise an effective pest by bringing in an infected parasitoid, by bringing in one that's not effective and they cross, you lose control of the existing pest.
Allister No, that's a very important point because that seems the most logical pathway, but it obviously shows that it's not as simple as that. Now, Stephen, there are other things going on in this area of parasite management and watching what you've just described to us in the Argentine stem weevil and it's parasitoid interaction. There's other things going on in New Zealand that's really important for the future.
Stephen And we're concerned about clover root weevil, partly because there's no endophyte for clover, root weevil.
Allister And if I can, I'll just describe that as well, because New Zealand, through its long phase of intensification of agriculture, has utilised nitrogen effectively to grow a significant amount of outdoor pasture or pasture. Sorry, not outdoor pasture, pasture in our temperate landscape. And this has allowed us to keep our animals outside for the majority of the year, feeding in a natural, very nutritious landscape. However, parallel to our grasses, we have really utilised clovers and New Zealand, particularly trifolium repens white clover. And especially as we're starting to get into the phase where we're focusing on the fate of nitrogen in our landscape, white clover is becoming more and more an important strategy to moderate the amount of synthetic nitrogen we are putting on our landscape. So the health and wellbeing of white clover is paramount at the moment, and unless I'm mistaken, a bit like Argentine steam weevil, but much more recent. We had a massive pest species arrive in New Zealand sometime possibly late eighties, early nineties.
Allister Mid nineties and came in through potentially one of our ports. And I was sort of involved right at the back in the summer of the road shows about its slow move across the country. But at that stage we were also seeing a lot of movement of dairy cattle as they were starting to populate different parts of New Zealand. So a lot of dairy cows were literally being trucked the 15 to nearly 2000 kilometres of the length of New Zealand from the Waikato where this pasture pest started in the Bay of Plenty. And I think what happened is that the weevil hitched rides on cows basically as they moved down throughout the south of New Zealand. So the weevil started to populate and the weevil and from an agronomic perspective, lays a white larvae that colonises the ground and eats the nodules off the white clover plant. And the root hairs of the clover plant, all of which if that clover then goes into a drought stressed environment, having its roots severely pruned by the larvae and having the nodules cut off, it has led to actually white clover being wiped out from our pastures, which leads to the primary control mechanism that was brought in. And the parallel between that and Argentine steam weevil.
Stephen Ellis Bay, all the details that are somewhat similar to what we're talking about with Argentine stem weevil, we do have a parasitoid is very similar to the one that we're talking about with stem weevil. We're entirely dependent on that Parasitoid it's pathogenic, it's clonal, and it's that sort of what there is between us and losing clover. And so we're worried. I mean, we've got selection pressure on the clover root weevil, not that different from what we saw in stem weevil. So the question is, what are we going to do? And I might say we're not doing much at the moment because we're not funded to do anything.
Allister Which is really potentially, as I described, you know, the importance of losing chemical treatment, which there was no chemical treatment for the clover root weevil. You know, really the parasitoid for the clover root weevil has been a huge solution. And I suppose this is the thing is we've only got one bullet in our gun and we've actually fired it. And so some of what we've already discussed today and the high level science behind the genomics that you've identified with Argentine stem weevil, I assume is one of our great hopes of taking the learnings that you and Otago University are finding and the genetic diversities that are coming from these clonal populations could be one of our great hopes for trying to manage its population in the future.
Stephen Yeah, we're doing a bit on the genetics, but not much and there's no crisis now. But there sure is hell will be if this thing gets out of control and we're not really doing enough to know what the alternatives are and what we can do about it if it ceases to be effective, is, again, a large group of us working on this or there has been many of the people have left or have been diverted to doing other things.
Allister Yeah. And so I suppose the nice thing about sharing the story actually is just to recognise that these things are hugely important. They are important for the sustainability of our agricultural system and the efficiencies in the case of clover usage in New Zealand to our agriculture sector. None of us want to go back to those landscapes that were stripped out of white clover. It was a very bad few years when we were losing all our clover and different regions of New Zealand, and that parasitoid could not have come at a better time for the country. And let's just hope that it doesn't follow the same path as Argentine stem weevil Parasitoid. But it does give me a little bit of hope that the science that you're doing on the Argentine stem weevil parasitoid failure will give us a head start to interpreting what's coming and maybe a head start to interpreting the solution.
Stephen There's obviously crossover, but they're both weevils. They're both the same genus of Parasitoid. We do have a start, but we're not actually doing a hell of a lot on it at the moment.
Allister And that's probably the big take home message. Yeah. So no, that's a really important awareness that the story hasn't finished with Argentine stone weevil at all. And in then clover root weevil was sitting there completely as a parallel story to the adventure we've just discussed.
Glenn This has been a fantastic podcast. I've actually learned a lot in terms of this. Summarise Allister, what are the key messages that have come from today?
Allister Well, if I was to start the process, I would look at the unique landscape that New Zealand is, we're very diverse, but we're very diverse in what's evolved here over millions of years and I believe as we evolved and became an agricultural country, we obviously brought in a lot of species to drive that agricultural development. And in doing that, we were an island without a lot of things here and everything's been brought in. And so that one of the big messages is that when a pest gets across our border, it has an absolute free lunch, a free ride, and it just explodes like nowhere else in the world. Really insignificant insect pests around the world come to New Zealand and just become a major economic pest. And what is so obvious is that the only way we can actually deal with some of these pests is to invest and going back into their home ranges and are, you know, thoughtfully reviewing and understanding their ecologies and what is out there predating on these or parasitising our pests in their worlds. Obviously, the process of bringing them back and doing due diligence is quite extreme. And over time, I imagine it's one of the bigger chores of one being excited about having an opportunity, but then recognising that it's going to target something that's too important to our economy to allow through the border. And so not everything that has the potential makes it. And then when it comes here that the message I've picked up from Stephen is that the same success story that can be linked to the pests being so successful and so damaging to our island nation also means that the Parasitoid can be actually surprisingly like world class controls. But then, like everything, we don't know the whole story until it unfolds. And what I've taken away from this is that, you know, it is a high five moment when we have such an incredible success story, relatively speaking. But after many, many generations of interaction, we have experienced and recorded and reported changes to the primary pest species that has seen it move away from the parasitoid in such a unique like world unique way, which I think is very exciting. Even though it's a story of a failure, it's still a scientific story that's very interesting. And so we've got a problem, a re-emerged. We are very lucky that our grasslands has another mechanism. We are lucky that we have insecticides available to us today, both in seed treatment and in pastoral landscape that have some ethics. But the writing is on the wall for some of those insecticides and this is what when we talk about the loss of insecticides from agriculture, these are the sort of conundrums that get unleashed because this is all happening in the background. Insects are in different cycles between being pests and being predated on or parasitised. And in the absence of those insecticides, we're going to unleash different things that we don't understand. In New Zealand, we're extremely lucky that we are world leaders in the endophyte technologies with between funguses, these fungal endophytes and grasses which provide a major mechanism for perennialty in the presence of Argentine steam weevil. But the parasitoid had made a massive impact on our landscape and its ability to tolerate storms of weevils. And so we are back in the bad old days of the pre nineties at the moment and our landscape, our endophyte technology is helping us, it's helping to moderate some of those impacts. But when a stem weevil storm arrives on a farmer's grassland it can be very very damaging. So I think that's probably covers an element of the story. But what I would also highlight and finish on is that this is an area that doesn't really get invested in the New Zealand funding system, but it's still of huge importance to an island nation like ourselves.
Stephen It's not being funded. And to the extent that it was in the 1990s. The other thing I need to say is there is a group of us doing this. It wasn't just me, you know, there was a large rocket base supporting me. The funding is very thin for this stuff now.
Allister Yeah. And when you think about what I've just said about insecticides and chemical controls and even some of the other sort of biocontrol options you have, I suppose what we've learned is that the best solution is a suite of options. And the only way you get multiple options is by funding and seeing value and all these things. And I honestly think that we haven't seen the full consequences of many of the world's decisions about the tools that are in the toolbox. And New Zealand is one of these vulnerable countries whereas we lose individual tools from a toolbox for controlling things, we can be very, very exposed at times.
Stephen Particularly in view of climate change as well. We've been looking at invasive species. We don't really know what we're going to get, let alone what we've got to control.
Allister And how far they travel. And so they're in someone's backyard yesterday, but they're in your backyard today. And that could mean a lot different to all of us.
Glenn Talking about backyards. It's been a really interesting podcast. I'm going to go now and to my lawn and see if I can find this sneaky weevil. Thanks, Steve. Thanks Al talk soon.
Allister Bye. Bye.
Stephen Bye. Thank you.