The cinnabar moth, Tyria jacobaeae (L.) (Lepidoptera: Arctiidae), an insect introduced for the biological control of tansy ragwort, Senecio jacobaea L., suffered considerable mortality at some study sites from 1967 through 1970. At the original site of colonization, one mile south of Fort Bragg, Calif., mortality was probably in excess of 85% in 1970. Factors influencing the mortality included predation by insects, sowbugs (Crustacea: Isopoda), and rodents, a microsporidian disease caused by Nosema sp., and some limited parasitism. Despite this relatively high mortality for an introduced insect, the cinnabar moth is well established in California, Oregon, and Washington. Populations have generally increased, and partial control of the pest plant is being obtained in some areas.