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The San Jose scale (Quadraspidioius perniciosus) is an injurious pest of deciduous fruit trees throughout the world, and is present to a varying degree in most orchard districts in New South Wales where pome and stony fruits are grown. It has a wide range of food-plants, including almond, apple, apricot, peach. pear, plum, prune and a great variety of introduced trees and shrubs. Hedges of tree lucerne may become seriously infested.
The scale develops on the trunk, limbs and twigs of the trees, and occasionally on the fruit. Once it is established, it usually increases very rapidly if control measures are not adopted, and may seriously injure or even kill the tree. Badly infested portions have a greyish, scurfy appearance, due to the presence of masses of minute scale coverings.
The fruits of apples and pears may also become infested with the scales, and this causes characteristic reddish blotches to appear on the skin, spoiling the appearance of the fruit.
The scale-covering of the adult is greyish, with a yellow or dark area in the centre, and is about one-twelfth of an inch in diameter. The scales of the young forms are dark or almost black. It obtains its food by inserting its fine, hair-like mouth parts into the tissues of the plant and sucking up the sap from the cells within.
The mature female produces live, active "crawlers". These make their way out from under the parent scale and, after moving about for a while, settle down, insert their mouth parts into the plant
and commence to secrete their own protective scale-coverings.
The female insect remains fixed in the one place for the rest of its life, but the minute male finally develops a pair of wings and emerges from beneath its scale.
The reproduction and development of this scale are comparatively rapid during the summer, the period from birth until young arc again produced being about six weeks. Thus several generations may be developed in a year and, as an individual female may produce as many as 400 young. the increase in numbers may he very rapid.