Story: Insect pests of crops, pasture and forestry
Armies of insects can infest crops and pasture, causing millions of dollars’ worth of damage. Mites, weevils, grubs and beetles nibble the leaves or suck the sap of a range of crops and pasture grasses, and some carry diseases.
Full story by Alison Popay
Main image: Codling moth caterpillar
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Insect pests damage crops, orchard fruit, vineyards and pasture, and cause millions of dollars’ worth of lost production each year.
Endemic pests of pasture
Some pests are endemic (found only in New Zealand), and have adapted to eating introduced pasture plants. They include grass grubs, porina, mānuka beetles and mealy bugs.
Introduced pests of pasture
A number of pests accidentally introduced from overseas eat pasture plants and have become a major threat to New Zealand farming. There are strict controls to make sure more pests do not become established in New Zealand.
Introduced pests which eat pasture plants or roots include clover root weevils, Argentine stem weevils and African black beetles.
Cereal crop pests
A number of insects eat crops such as wheat, maize and barley. The greasy cutworm bites off maize shoots, while aphids suck the sap of cereal plants and spread disease.
Fruit and vegetable pests
Apples and kiwifruit are New Zealand’s highest-earning export crops, but if the fruit has been damaged by insects it cannot be exported. Leafroller moths, codling moths and scale insects can stunt plant growth, scar the outside of fruit, or burrow into it.
The white butterfly eats cabbage and broccoli, while the tomato fruitworm attacks a range of vegetables including tomatoes and corn. Potato tuber moths are a major pest, and tiny mites damage vegetable crops by feeding on their juices.
In the past, the chemical DDT was sprayed over pasture to kill insects, and other insecticides were used on fruit and vegetables. However, the insects became resistant and chemical residues were shown to harm the environment and people. Now, farmers aim to kill pests using natural methods, such as releasing insects or bacteria that attack the pests.