Most of the pests of plants, animals, or man are recent introductions, almost without exception having been introduced unwittingly by man over the last 150 years.

Control

Chemicals: The use of insecticides is controlled by the Agricultural Chemicals Board. Some chemicals are prohibited and regulations are made from time to time governing the use, application, and rates of insecticides.

The following pests in New Zealand are known to have become resistant to insecticides.

Housefly (Musca domestica) against DDT and Dieldrin; Blowfly (Lucilia sericata) against Dieldrin; Leaf roller (Austro-tortrix postvittana) against DDD; European red mite (Panonychus ulmi) against organo-phosphorus sprays; Two-spotted mite (Tetranychus telarius) against organo-phosphorus sprays; Midge (Chironomus zealandicus) against Dieldrin.

Biological control: The following are some of the cases of attempted control of insect pests by specially introduced insect enemies which have shown a worth-while degree of success.

Woolly aphis (Eriosoma lanigerum) by Apelinus mali; Cottony cushion scale (Icerya purchasi) by the ladybird, Vedalia cardinalis, and the fly Chryptochaetum iceryae; Gumtree scale (Eriococcus coriaceus) by the ladybird Rhizobius ventralis; White butterfly (Pieris rapae) by the pupal parasite (Pteromalus puparum).

Plant resistance to pests: Some resistant plants have been introduced, notably apple stocks resistant to woolly aphis and grape stocks resistant to phylloxera. Plants have been bred for resistance to insects especially brassicas, beans, and cereals.