To this day Dr Stephen Goldson remains flabbergasted by the success of a scientific project which by any count should have been doomed to failure.
The punt to put a noose around three types of introduced weevils has paid off with farmers no longer looking at costs of $400 million to $500m each year from their pasture carnage.
Much is at stake.
On top of pastures being ripped to shreds, insecticides were unviable because their sprawl over a massive land size was too great to control.
In the end, minuscule biocontrol agents - three types of tiny parasitic wasps - were all that stood in the way of introduced weevils continuing to have their hungry way.
Free of natural predators, they would otherwise have continued taking their unaccountable toll on pasture production.
On paper, the odds of finding tiny wasps with the parasitic clout to beat up the pests, let alone releasing them to establish colonies in a foreign environment were stacked against Dr Goldson, now an AgResearch emeritus scientist, and his team.
From early on, he rated the chance of success as "very, very low".
He had no idea it would produce such an overwhelming result so soon.
"The big surprise for me, well, first of all was that it worked and we got a three out of three success. The clover root weevil, the Argentine stem weevil and the lucerne weevil, all three were beaten by different variations of the parasitoid wasp called Microctonus.
"The chances of that result is one in 1000. It’s probably one in 10,000 that we were going to get that result if you put in statistics where biocontrols have actually had a major effect.
"It caused me and the group bathing in this success to ask the obvious question: what the hell is going on?"
By the numbers, the odds of any one of the parasites succeeding against any one of the three weevils was one in 10. So to get all three right was 10 by 10 by 10 and the odds raise to one in 1000.
Such high odds failed to deter them from starting out in the first place.
Dr Goldson said they had nothing to lose and the problem for each pest was so severe they had to at least give it a go.
The Argentine stem weevil had an endophyte - a fungus found naturally in some pastures helping to protect plants from insect damage - to curb to some degree its explosion. The other two weevils had nothing preventing their bloated numbers from swelling and colonising new ground.
"It was really serious," he said.
"Stem weevil even with an endophyte was costing $200m to $300m a year destroying pasture, forcing the need to renew pastures and damaging seed establishments. And the endophyte doesn’t work as well in some grass rotations sometimes so there’s a whole range of things. In the end it was worth trying to bring in things that could work."
Furthermore, more nitrogen would have gone on pastures, yields would have spiralled downwards and struggling ryegrass and clover would have been crowded out by brown top and a rag tag of lesser grasses.
Fortunately for farmers, the parasitoid wasps are the natural enemies of the weevil trio. After seeking them out, they sterilise and kill the pests by laying eggs inside them.
Female wasps sourced from nine different locations in South America were raised and released in population groups - one in Uruguay, two in Argentina and others in Brazil and Chile. In equal numbers from these areas they were released in New Zealand.
This work did not happen all at once. A biocontrol wasp for the lucerne weevil was initially brought in by a government science agency in the early 1990s with Dr Goldson involved in this work.
He led the science to bring in biocontrol agents for the other weevil pair.
Nor were the initial signs of parasitism for the stem root weevil in South America promising.
Parasitised levels within its population were about 10% and needed to be more like 60% to 70% to push weevil numbers down so they could not reproduce and snuffed it.
Without slugging them hard, they just compensate for small losses by reproducing faster.
As if the mission was not already on a knife-edge, it should be remembered just three different types of parasitic wasps - one for each weevil - were brought in. Scientists looked in 10 countries alone in Europe to identify one of them and only came up with the trio, before funding dried up for further searches and the urgency went on to make them work.
So why was it so successful?
"It’s not because we were brilliant. We were incredibly professional and careful in how we did all the rearing and distribution all the time because we had all the problems with the threat of it attacking native weevils and Environmental Risk Management Authority [involved].
"So we did it and got good results, but we could’ve done it well and got no result."
Over the past 10 years he has pondered on the answer to reach a clear conclusion.
It lies in our simplified eco-systems and the mismatch of few natural enemies.
"Our farmlands are transplanted from a few plant species from Europe. They’ve gone into a completely alien eco-system - that is New Zealand forest and tussock. So we have all this plantation of ryegrass, clover and several other plants going into New Zealand from northwest Europe and the whole of the Palearctic and we had great performance from those plants.
"But they were left wide open to invasion because amongst them there were no natural enemies to take out the weevils. The weevils went bonkers because there were so many holes in the eco-system and they built up to numbers possibly hundreds times higher than they are in their native range."
At their peak, 600 to 700 stem weevils could be found in a square metre, whereas in their home country Dr Goldson struggled to find any of them.
By the same token, the natural enemies of native weevils evolved and stayed in native forests, unwilling to migrate into introduced pasture eco-systems.
"The fact that the weevils did really well is they had no real opposition. The reason the parasitoids did really well is they didn’t have any problem either. They came bumbling into an empty eco-system as well, stuffed full of prey.
"They came in and had a huge free lunch because there were massive numbers of weevils around. The stem weevil parasitoid in its place of origin had about 35 days to lay all of its 40 to 50 eggs after having to search for weevils.
"In New Zealand, with wall-to-wall weevils, the parasitoid was found to run out of eggs in 10-15 days."
Finding parasitoid wasps was no easy matter. At one stage a parasitoid called Microctonus aethiopoides was identified as active against the clover root weevil in Europe, but had to be dismissed as they would have crossed with another strain of Microctonus aethiopoides that had already been brought in to New Zealand from Australia to control the lucerne weevil. It was found that when these two strains were crossed the offspring had no effectiveness and ended up being useless.
Therefore, the team had to scour Europe again and uncovered a suitable strain of the parasitoid in western Ireland that would not cross with the lucerne parasitoid strain.
For the Argentine stem weevil Dr Goldson travelled to South America - twice for three months - in the late 1980s to find a suitable candidate.
Of odyssey proportions, his efforts took him to many parts of Brazil, Uruguay, Argentina and Chile in the search to find Microctonus hyperodae.
Step one was locating the weevil in its native range of the swamps and boggy valleys of the Andes.
A romanticised picture would have him traversing the vast mountain chain in a race against the clock.
Search he did, but they were not there. The reality was boxes of weevils and countless other flying insects were opened up in his hotel after being collected with a butterfly net at night by sweeping picnic areas and football pitches.
Even these evening excursions had their dangers when South American countries were rolling over their general leaders and on edge.
Captured weevils were carefully dissected under microscope, again in the hotel room, night after night to reveal the parasitoids.
By plane they were sent to New Zealand in the drinks cabinet to maintain a non-terminal temperature. On arrival, $1m was spent to keep them under strict quarantine for a year before their release.
Fortunately for the scientists success came early and the track they were on was recognised as valuable.
Dr Goldson said the decision makers of the 1990s took the risk to back the project and after wasp numbers built up in less in two years ongoing funding was secured.
The project showed there was a need for sensible long-term science, he said.
As well as restoring depleted pastures, the wasps reduced insecticide use and prevented chemicals entering the environment.
In the climate change stakes a lower pest burden on grazing plants increases pasture persistence which reduces the cultivation of soils and the release of soil carbon.
Some of the team behind its success have since scattered to other corners of science or retired, but Dr Goldson has carried on in his mostly unpaid emeritus role.
"The worry is if you are looking at clover root weevil control the existence of our white clover hangs on one parasitoid wasp and if something happens, say the Irish ones become sexually reproducing and become all muddled up with the ones under lucerne then we have a big problem with lucerne and in pastures. So that’s why I think part of our biosecurity obligations is to understand the dynamics with the pests we’ve got in New Zealand as well as keeping them out."
So the job is not done and biocontrol research has become the launching pad for a new genetic direction.
Dr Goldson is carrying on this work with Otago University’s biochemistry department in a $2m project.
The work includes matching the genetic potential of parasitoids already here, and those that might later arrive, to become more efficient and reliable, matching them for different regions and possibly even making a start on selecting and breeding the most virulent.
"So we are starting to understand the genetic mechanisms behind some of the results we’ve been getting and what pre-disposes the biocontrols’ success and whether different races, if you like, matter when we talk about a single control agent like the agent we have for a stem weevil or a clover root weevil or a lucerne weevil. So really we’re looking at the variation within the biocontrol agents for each of those three pests and try to work out how to optimise decision-making around the next biocontrol agents we need to work on."
By a stroke of good reasoning by the team, rather than luck, all of the wasps found inside weevils from South America were placed in a deep freeze to allow their genome sequencing.
After 1 million were reared and released into New Zealand, scientists still did not know exactly which lines of each population had been released.
That is because the wasps almost always produce clones of identical daughters so, for all they knew, they could have brought in 40 of the same females, or 40 different females, because they could not tell them apart.
The parasites still have the machinery to be males, but the switches to do this are virtually turned off. A mother producing female clones will occasionally bear the odd impotent male before it withers away.
Scientists looking at their DNA, and the components for sexual reproduction, now believe they might be able to turn the male genes on in the clones which means they can start to select for virulence.
Dr Goldson said this was the type of future science they were working on to safeguard future attacks.
"There are 100 species very much in the same bracket as the Argentine stem weevil on its own and a lot in lucerne and clover and a bunch of them in America so this is where the biosecurity thing comes in.
"We’ve targeted the three weevils because they busted through our border biosecurity. There’s dozens of them in the United States which are under better control there because they have more natural enemies than we’ve got so we can use the success of this work as models for designing reaction to other invasive species."
In the meantime, the Dr Goldson-led team now has the genome sequencing to trace their heritage and see which ones did best, and where, by looking at their traits.
After their release into New Zealand, they wanted to know, for example if the wasps from South Brazil performed better in Northland or the ones from Patagonia succeeded the most in Otago.
They could not answer that question at that stage because they could not tell them apart.
Now they can because they have their whole genome sequencing and the use of DNA to classify them into different groups and compare them.
Dr Goldson said the results so far were good and bad.
"We’ve confirmed without any doubt at all that the parasites we collected from the west of the Andes are different from east of the Andes. So Chile’s on the west and Argentina, Uruguay and Brazil on the east. So we are starting to show that there are, if you like, evolved differences between these different places and that confirms some early work."
A troubling discovery has added urgency to developing new environmentally-friendly methods to counter the pests.
About eight years ago they found the Argentine stem weevil reacted to its parasitoid by becoming resistant to them.
Selection pressure by the wasp on the weevil was so great it developed the ability to ward it off. This was more visible in the north where it was hotter with parasitism now down to about 14%, he said.
"So this is the first time it’s ever been discovered actually in the history of the world. I was the only one excited about it because it highlights the need to get into genetics so we can understand what the hell is going on and also highlights what else you can do with the genetics if and when we get permission to do gene technologies."
Scientists have yet to find the gene behind this resistance and were still looking to see if it was triggered by a virus.
Dr Goldson said future science needed to work out the possibilities.
Born in Liverpool and moving to Auckland at a young age, he wanted to be a journalist before a year as a school-leaver on Volunteer Service Abroad in biodiversity-rich Sarawak convinced him otherwise. He studied science at university in Dunedin and Christchurch before carrying out a PhD study in entomology at Lincoln University.
When he began as an entomologist in the Ministry of Agriculture’s research division he could be found in a laboratory measuring the ovary lengths of weevils to see if they had mated. Deemed by a colleague to be luxury research going nowhere, these small beginnings have grown to a 47-year career.
His career has included being the strategist for the chief science adviser to the Prime Minister for nine years.
So it is no surprise that Dr Goldson was the supreme award winner at the 2023 Science New Zealand Award.
Judges praised him for standing out among finalists, for the economic and environmental benefits of his work and the excellence of his research over a long period.
Particularly gratifying for him was also winning the Ray Brougham Trophy, an award given out by the New Zealand Grassland Trust, as it recognised the entomology work by him and the team.
Dr Goldson has no immediate plans of stopping any time soon. The emeritus role is unpaid, but means he can use AgResearch’s laboratories, library and IT services and can continue his weevil work. Funding from other projects is covering his operation costs.
"It’s been great that I can carry on the work that I’ve been doing for a long time because it’s making real progress still. So, I really want to see what happens."
