Promotes the emission of terpenes volatile organic compounds (VOC) in response to damage mediated by arthropod herbivores (e.g. Tetranychus urticae), probably to attract natural enemies of the herbivores. (2E)-geranyl diphosphate = diphosphate + tricyclene (2E)-geranyl diphosphate = (E)-beta-ocimene + diphosphate Binds 3 Mg(2+) or Mn(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Accumulates in response to Tetranychus urticae (two-spotted spider mites) infection, and transiently after mechanical wounding and upon treatment with alamethicin (ALA), a potent fungal elicitor. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family. Tpsb subfamily.