The suppression of the cottonycushion scale, Icerya purchasi, by the vedalia beetle, Rodolia cardinalis, in California citrus groves in 1889 is unparalleled in the annals of entomology for its drama, human interest, political ramifica tions, and continuing significance. This spectacular demonstration of applied ecology established the practical ity of biological control, which was singled out as the preferred pest control method of the Entomological Society of America in 1964 (22). During the past 100 years biological control has been widely, repeatedly, and thoroughly tested. So this review of the vedalia beetle is entirely appropriate as a celebration of the centennial of biological control. Biological control has proved superbly successful in an array of diverse situations. It has succeeded in both temperate and tropical climates; on continents, subcontinents, and islands; and in both northern and southern latitudes. It has suppressed target pests of great taxonomic diversity. It has worked well in depauperate biotas and in those of great complexity. It has been a boom to primitive agriculture and has been economically successful in