A new alkaloid, chilocorine B, was characterized from a coccinellid beetle, Chilocorus cacti. This compound represents the first spirocyclic example of the new ''dimeric'' alkaloid family whose structures are derived from two thirteen-carbon tricyclic subunits, 2-methylperhydro-9b-azaphenalene and 3,4-dimethyloctahydro-8b-azaacenaphthylene.