Drawing from a four-year study of US science institutions that support biological control of arthropods, this article examines the decline in biological control institutional capacity in California within the context of both declining public interest science and declining agricultural research activism. After explaining how debates over the public interest character of biological control science have shaped institutions in California, we use scientometric methods to assess the present status and trends in biological control programs within both the University of California Land (...) Grant System and the California Department of Food and Agriculture. We present available data on the number of scientific positions and the types of positions to discuss the impact on the amount of public interest research on biological control in California. We use sociograms to depict how biological control science networks have been reconfigured over time. Our quantitative and qualitative analyses indicate that the following factors contributed to the decline of biological control science in California over the 45-year period analyzed: (1) the institutional reconfiguration of university research priorities; (2) the fraying networks within and increasing specialization of biological control science; (3) the transformation of the social organization of the life science work, including privatization; and (4) the abandonment of this thematic area by civil society activist groups. This broad array of forces suggests that biological control, as a public interest science, will require a deliberate intervention, based on advocacy of clear public interest criteria. (shrink)