A program of mass production and periodic release of imported Stethorus sp., a predator of tetranychid mites, is being conducted by the University of California Department of Biological Control. Large numbers of the Pacific spider mite (Tetranychus pacificus McG.) are reared on linted oranges, under controlled conditions. The mite-infested fruit is used to mass-produce the Stethorus sp. in specially designed rearing units. The Stethorus adults are collected from the units and released on mite-infested plants.