Geranyl diphosphate synthase involved in pheromone biosynthesis. dimethylallyl diphosphate + isopentenyl diphosphate = (2E)-geranyl diphosphate + diphosphate Binds 2 Mg(2+) ions per subunit. Pheromone biosynthesis. Specifically expressed in the anterior midgut of male beetles, the site of aggregation pheromone biosynthesis. Specifically induced in the anterior midgut of males (PubMed:15983375). Expression levels are regulated by juvenile hormone III (JH III) (PubMed:15983375). 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 FPP/GGPP synthase family.