Developing successful biocontrol for pasture pests

The parasitoid Microctonus aethiopoides (left) stalking its host the clover root weevil (Sitona lepidus)

Pastoral ecosystems cover over half of New Zealand’s land area and contribute massively to our economy. Thus, farmers and scientists have always been keenly focused on methods of controlling pests that attack pasture.

Until the 1970s, pasture pest control was mostlyachieved through widespread application of organochlorine insecticides such as DDT. However, the environmental effects of these chemicals eventually became apparent and, by the 1970s, there was a rush to find alternatives.

Biocontrol was one such development. The principle of biocontrol is simple: go to where the pest came from, find a natural enemy and bring it back for release. However, in practice it is not so simple because a myriad of things can go wrong. For example, the agent may not establish in the new location or, if it does, it may not attack the right pest. It may go crazy and attack everything, or it may focus on a native species you had not anticipated that it would like and thus threaten biodiversity.

As a result, finding useful biocontrol agents is often extremely difficult. Over the last 100 years, typically only around 20% of biocontrol agents have successfully established and barely 20% of those that did establish later turned out to be useful.

These low success rates highlight the great achievements that AgResearch scientists have made in this field since the early 1980s. The Biocontrol & Biosecurity Section has developed three highly successful biocontrol programmes, in each case using a tiny, genetically related parasitoid wasp to suppress an introduced weevil pest.

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