Sesquiterpene synthase involved in the biosynthesis of volatile compounds. Mediates the conversion of (2E,6E)-farnesyl diphosphate (FPP) into (1E,4E,8E)-alpha-humulene and (-)-(E)-beta-caryophyllene, and of (2Z,6Z)-farnesyl diphosphate ((ZZ)-FPP) into beta-bisabolene, gamma-curcumene and (Z)-gamma-bisabolene. Can act with a low efficiency as a monoterpene synthase with geranyl diphosphate (GPP) as substrate, thus producing beta-myrcene, (E)-beta-ocimene, limonene and terpinolene