Red scale (Aonidiella aurantii) is the most important insect pest of citrus trees (orange, mandarin, lemon, grapefruit) and may occur wherever these trees are grown. It is more important in inland areas but may be destructive in coastal districts in dry seasons or where heavy deposits of dust occur on the trees, e.g., where trees are grown along roadways or fowls run in the orchard.

All the aboveground parts of the tree may be infested and if unchecked heavy leaf fall and dieback of twigs and branches may occur, whilst young trees may be killed outright. Heavy scale infestation on the fruit may cause the skin to become pitted arid roughened and fruit may remain undersized and crack badly.

The soft yellowish female insect develops beneath the circular reddish scale covering and when mature is fertilized by the tiny winged male scale and then produces live active six legged progeny or " crawlers ". These crawl about for a day or so before settling down in their permanent position where they insert their sucking beaks into the plant tissue and feed on the sap. The period from the settling of the female crawler to the production of the next generation of young scales is about three months in the warmer weather and several generations of scales may occur each year.