The citrus gall wasp (Eurytoma frills) is a pest of citrus trees on the north coast of New South Wales, and in recent years has appeared in many parts of the metropolitan area, from Hawkesbury River to Sutherland. Until recently it had not been found in any of the important citrus-growing areas of the State, but some limited infestations have been discovered in backyard trees in the Gosford-Woy Woy area.

This wasp is a native species which originally bred in various native citrus trees. Although all kinds of citrus trees are susceptible to attack, and heavy infestations frequently occur, especially in cultivated lemon varieties and in grapefruit, the common or rough lemon is preferred above all others.

The injury is caused by the female wasp depositing eggs within the stems and subsequent development of the wasp hum. The injury is particularly serious in nursery stocks, as the main stems may be attacked.

The eggs are deposited between the bark and the wood and each female may lay more than 100 eggs. Young twigs, only a few weeks old, are selected for egg-laying.

There is only one generation a year, and the wasps emerge from the galls mainly during the months of October and November and are ready to deposit their eggs immediately. Gall formation does not become evident until several months after the larva' have hatched. The pupal stage lasts about one month and the life of the adult is about one week.