AgResearch has invested considerable effort into its biological control of pasture pests programme.  Not only has its research paid dividends in improved pastoral production resulting from successful control, it has established world-leading capabilities that are proving their worth in fighting the invasion of new pasture pests.

A biological control agent AgResearch introduced to suppress the Argentine Stem Weevil, for instance, is saving New Zealand at least $50 million a year in improved on-farm pasture and livestock production and sustainability.

Background

Scientists in AgResearch’s Biocontrol and Biosecurity Group have been at the forefront of past management research for over 25 years

The management of pests is practised under constantly changing conditions.  Focus has shifted over the last 20 to 30 years, from agrichemical management, to detailed analyses of the ecology and behaviour of undesirable species as a basis for safer, biologically-based management systems.

Existing pasture pests are estimated to cost New Zealand  over $1 billion a year in lost production.

And there are around three new invertebrate pest species establishing themselves in New Zealand each year, alongside new weeds and pathogens.  Some of these will have potentially devastating impacts, requiring urgent and carefully-researched management approaches

Strategies for pest management are critical for a country so reliant on primary production. The development of biological control systems contributes to New Zealand’s on-going pest management, enabling the country to enhance its position as an exporter based on residue-free primary production.

The challenge

Biological control in pasture simply means the introduction of a natural enemy such as a parasitoid, that will specifically kill a particular pasture pest and suppress the pest population to levels below where damage occurs.

The difficulty with the effective introduction of a biological control, is the range of detailed knowledge required for it to be successful.   It’s not simply a matter of purchasing a suitable agent as you would a fertiliser, and spreading it onto pasture.

It can take around a decade of investigation, solid research, and trials before properly understood and integrated control becomes a reality.  Knowing there’s a pest ripping through hectares of prime pasture is just the beginning. 

There is a whole area of research known as population ecology, which covers areas such as population dynamics, key mortality factors, seasonal behaviour, damage relationships with plants, migratory habits and temperature-development relationships.  Population ecology is needed if effective pest suppression is to be achieved in a way that is understood and therefore optimal.

Then there’s the search for a suitable biocontrol agent, which usually takes researchers back to pasture pest’s geographical area of origin to discover its natural enemies.

Applications to the regulatory authorities follow, with the next step being to import likely agents for detailed quarantine assessment.  The scientists need to see the extent to which the control agent impacts on the pasture pest concerned, but they also need to understand its interactions with our environment.  They need an accurate overview of the ecosystem, and an understanding particularly of the likely impact on native insects which may not have immunity to the introduced predator. They also need to understand its attacking and feeding behaviours, and whether the natural enemy will synchronise with the target pest. 

Genetic diversity is important for such studies.  Research has unearthed “quirky” situations where parasitoids are very effective in controlling one species of pasture pest, but have no effect on very similar populations elsewhere.  Building up capability in DNA studies for this sort of understanding has been something AgResearch’s biocontrol group has led in over recent years.  They have recognised that it is necessary to understand the genetics of biocontrol agents and pests if the best choices are to be made.

And if all the years of laboratory-based studies proves successful, the biological control agent will be mass reared for field trials and potential widespread release.

Outcomes

Not all biocontrol programmes are effective, but the Lincoln-based Biocontrol and Biosecurity Group has an enviable track record, which may reflect the effectiveness of their research.  The group is conscious of the role it has played in keeping destructive pasture pests at bay historically, and for its continuing responsibility in biocontrol of pests and weeds that are being unintentionally introduced to New Zealand now.

Argentine Stem Weevil            AgResearch successfully conducted a painstaking research programme to control Argentine Stem Weevil,  a pest considered New Zealand’s worst, costing over $100 million in lost pasture and crop production a year since it was accidentally introduced from South America around 1910.

The parasitoid wasp AgResearch introduced as a biological control  in 1991 has now spread throughout New Zealand, thanks to farmers groups which paid for the parasitic wasp and ensured its widespread release.  That effort resulted in major reductions in Argentine Stem Weevil populations – to the point where impact has often been substantially reduced.

The successful release followed expeditions to the weevil’s homeland to find a suitable parasitoid, followed by exhaustive safety testing back in New Zealand to ensure it was lethal to the specific pasture pest, yet environmentally friendly in New Zealand conditions.

Lucerne weevil                     In the 1980’s, the Biocontrol and Biosecurity Group worked on the successful biocontrol of the pasture pest lucerne weevil, an introduced pest that also played havoc with New Zealand lucerne.  This weevil is also not a problem now, thanks to the predator parasitoid.

Clover Root Weevil            Clover root weevil is a more recent unfortunate introduction, having first been identified in New Zealand in 1996. The voracious pest has spread throughout the north and central North Island, and, given its hardiness, it is predicted it will only be a matter of time before the weevil establishes throughout New Zealand.  As so often happens, the weevil has come into New Zealand without any of its natural enemies.

                                       An integrated research programme was rapidly set up to look both at immediate management options for farmers faced with the pest, and at a longer-term biological control for clover root weevil.

                                       Population studies have begun, and interesting data has been discovered on the weevil’s relationship with the environment - high rainfall means a population explosion of clover root weevil, while dry conditions lead to the converse. 

And already the Biocontrol and Biosecurity Group have tracked down a very promising parasitoid from Western Ireland.  At the same time, strains of a particular fungus found in New Zealand and UK soils have been found to be effective in killing clover root weevil adults and larvae in the laboratory. 

Studies on all of these options are continuing.