Odorant-Binding Protein MsutOBP13 Mediates the Detection of Stress-Associated Host Volatile β-Ocimene in Female Monochamus sutor

Plants emit volatile organic compounds (VOCs) under stress, generating complex blends that mediate defense and insect host location. β-Ocimene is a widespread stress-associated monoterpene induced by herbivory, mechanical damage, heat, and drought, and influences insect behavior; however, its molecular detection as a kairomone remains unclear. Using the Eurasian longhorn beetle Monochamus sutor, we found that females are significantly attracted to β-ocimene. Antennal transcriptomics and expression profiling identified candidate odorant-binding proteins (OBPs), among which MsutOBP13 showed high binding affinity for β-ocimene. Structural modeling, molecular docking, and mutagenesis identified Phe49 as a key residue for ligand recognition. RNA interference further confirmed that MsutOBP13 contributes to β-ocimene-mediated behavioral responses. These results reveal a molecular basis for β-ocimene detection and identify this volatile as a host-location cue in a wood-boring herbivore.