SCALE INSECTS are among the most serious pests known to agriculture, and San Jose scale, Quadraspidiotus perniciosas (Comstock), ranks as the primary scale pest on deciduous fruit and nut trees. It is distributed worldwide and has been collected from approximately 700 different hosts. Unlike many insect pests, San Jose scale has the ability to kill all or parts of infested trees, in addition to making infested fruit unmarketable.