Promotes the emission of terpenes volatile organic compounds (VOC) in response to damage mediated by arthropod herbivores (e.g. Spodoptera exigua), 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. Expressed in leaves. Accumulates in response to wounding, methyl jasmonate (meJA) and infection by Spodoptera exigua (beet armyworm), a lepidopteran herbivory. Also induced by lepidopteran oral secretions. 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.