Maximum-likelihood dendrogram based on protein sequences of candidate odorant binding proteins (OBPs). Included are OBPs from Ips typographus (Ityp), Dendroctonus ponderosae (Dpon), Tribolium castaneum (Tcas) and Drosophila melanogaster (Dmel). One major beetle-specific expansion of Minus-C OBPs is evident. Bark beetle proteins in this expansion have lost cysteine residue C2 and C5. Two OBPs in I. typographus and one in D. ponderosae belong to the Plus-C group characterized by additional cysteine residues. Numbers refer to support values, which are only displayed when <; 0.9.