KEY POINTS:
On a farm in Patoka, Hawkes Bay, a future without chemical pesticides is beginning to take shape.
Here scientists are trialling one of a new breed of "bio-controls" to replace traditional pesticides that can produce harmful side-effects for the land and people on it.
The farm is one
of thousands affected by the invasion of the destructive clover root weevil.
The weevil larvae attack clover underground, reducing clover growth, especially in spring and early summer.
On pastures infested by the weevil, less clover means livestock have slower weight gains and produce less milk. In normal circumstances, a chemical spray might be used to kill a pest like this weevil.
But instead, scientists from the AgResearch crown research institute took a different tack.
They introduced a wasp native to Ireland, known as microctonus aethiopoides, on to the farm in January last year.
This wasp strikes at the adult weevil, injecting one or more eggs into its abdomen. This makes female weevils sterile, thus breaking the weevil life cycle. The wasp larva grows inside the weevil and kills it, when during the last larval stage it bursts out of the weevil's body.
AgResearch has just announced that since the introduction of the wasp, the autumn weevil population on the farm is down by more than 75 per cent, and 86 per cent of the remaining female weevils are sterile.
The wasp is also making major inroads at three other experimental release sites on different types of farming country in the North Island.
"Obviously the wasps are better at finding weevils than we are," said AgResearch programme leader Pip Gerard.
"We are now very confident that the Irish wasp will provide useful control of clover root weevil throughout New Zealand."
AgResearch chief scientist Dr Stephen Goldson said three new methods were being developed to replace the conventional pesticides.
These included release of fungi and diseases that specifically attacked a pest, producing crops that were more resistant to pests and bio-controls using the natural enemies of the pests such as in Patoka.
In many cases, sprays that posed a threat to the environment could one day be phased out, Dr Goldson said.
"We are looking for things far less toxic and reasonably specific to things we are looking to control."