For nearly thirty years, olive scale, Parlatoria oleae (Colvée), has been the most important insect pest of olives in California. Prior to the introduction of the Persian wasp, Aphytis maculicornis (Masi), in 1952, olive scale was also a most serious pest on deciduous fruits and many species of ornamentals in the Central Valley area. Since then, establishment of the Persian wasp, as well as one other parasite, Coccophagoides sp., has drastically reduced the severity and frequency of scale infestations in California, as reported in this study.