A new cytotoxic himachalene sesquiterpenoid 4alpha-methoxy-5,9-oxahimachal-9-ene (hugonianene A) which exhibited moderate activity against Anopheles gambiae mosquito larvae after 24 h at a concentration of 0.237 mg mL(-1), and at 48 h and 72 h contact time causing complete larval mortality up to a concentration as low as 0.01369 mg mL(-1), was isolated as the major constituent of the cytotoxic root bark extract of Hugonia busseana. Hugonianene A was obtained together with the hitherto unreported rosane diterpenoid 18-hydroxyrosane, the known rosane diterpenoid hugorosediol, an inseparable mixture of 12-methoxy-13-methylpodocarpa-8,11,13-trien-3,7-dione and 12-methoxy-13-methylpodocarpa-1,8,11,13-tetraen-3,7-dione, and the di-podocarpanoid hugonone B that was previously obtained from H. castaneifolia.