Identification of attractants for adult Euplatypus parallelus based on the interaction between odorant-binding protein 6 and semiochemicals

Euplatypus parallelus , a major pest of rubber trees, has inflicted severe damage on the natural rubber industry in Hainan Province. Odorant binding proteins (OBPs) play a crucial role in insect host plant location and serve as potential targets for attractant development. However, the interactions between E. parallelus OBPs and host plant volatiles and pheromones remain largely unexplored. In this study, we identified and characterized EparOBP6 as an antennal binding protein II (ABPII), a protein subfamily typically involved in the detection of host plant volatiles and pheromones. Fluorescence competitive binding assays showed that EparOBP6 binds strongly to several rubber tree volatiles, notably (+)-longifolene, β-ionone, cinnamyl acetate, and α-copaene. Molecular docking revealed eight key amino acid residues critical for ligand binding interactions. Electroantennography (EAG) and Y-tube olfactometer assays confirmed that β-ionone and cinnamyl acetate elicited significant electrophysiological and behavioral responses in both male and female beetles, whereas 1-naphthaldehyde primarily attracted males. RNA interference experiments demonstrated that silencing EparOBP6 in males significantly reduced their attraction to β-ionone and cinnamyl acetate, confirming the essential role of EparOBP6 in detecting these compounds. Field trapping experiments validated these laboratory findings, showing that traps baited with β-ionone and 1-naphthaldehyde captured significantly more male beetles compared to the control. These findings offer the first comprehensive insights into the olfactory mechanisms of E. parallelus , highlighting the essential role of EparOBP6 in mediating specific host-seeking behavior. This study provides a foundation for developing semiochemical-based pest management strategies for effective monitoring and control of this pest.