San Jose scale, common name for a scale insect, Aspidiotus perniciosus, introduced from China into San Jose, Calif., c.1870 on nursery stock. The insect has since spread throughout much of the United States and Canada. It is found in the commercial fruit-growing areas throughout the world and is a serious pest of apples, pears, peaches, plums, sweet cherries, gooseberries, and many other trees and shrubs. Only the winged males and young scales are mobile. The young nymphs, or crawlers, move about for a few hours in search of a good feeding spot; then they molt, lose their functional legs and antennae, and secrete a resinous waxy shell, or armor, under which they feed by sucking the sap of the host plant until they become adults. The sedentary female mates and gives birth to several hundred living young while still securely under the protection of the scale, which it never leaves. Two to six generations are produced per year, with an estimated 30 million progeny possible from a single female during one year. Infested trees show a decrease in vigor, take on a gray appearance from the low, conical, overlapping scales, and eventually die if the scale is not controlled. The pest is dispersed by being carried on the bodies of larger insects, on the feet and beaks of birds, by wind, and by shipment of infested nursery stock. The San Jose scale is classified in the phylum Arthropoda, class Insecta, order Homoptera, family Diaspididae.
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