Abstract: 【Aim】 To clarify the expression of the odorant binding protein MmedOBP18 inthe antenna of Microplitis mediator, and to investigate the ligand binding characteristics of the recombinant MmedOBP18. 【Methods】 The recombinant MmedOBP18 of M. mediator was expressed in the prokaryotic expression system. The localization of expression of MmedOBP18 inthe antenna of female wasps of M. mediator was evaluated using fluorescence immunohistochemistry assay. The binding characteristics of the recombinant MmedOBP18 protein to 99 candidate ligands were analyzed by fluorescence competitive binding assay. 【Results】 The recombinant MmedOBP18 protein was successfully expressed in the prokaryotic expression system. The immunofluorescence localization result showed that MmedOBP18 was mainly expressed in the lymph of sensilla basiconica type I of the antenna. The recombinant MmedOBP18 could strongly bind with 16 kinds of ligands. Among the low volatile compounds, 2-tridecanone, dodecyl aldehyde, myristic acid and undecylic acid showed the strongest binding capacities to the recombinant MmedOBP18, with the dissociation constant (Ki) values of 5.21, 6.42, 6.49 and 6.58 μmol/L, respectively. The non-volatile compounds palmitic acid, gossypol, quercetin and linolenic acid also showed strong binding capabilities to the recombinant MmedOBP18, with the Ki values of 3.86, 5.07, 5.08 and 6.51 μmol/L, respectively. In addition, the lepidopteran pheromone components (Z)-9-tetradecenal and (Z)-11-hexadecenal also showed strong binding capabilities to MmedOBP18, with the Ki values of 9.09 and 11.67 μmol/L, respectively, suggesting an important role of MmedOBP18 inhost localization. 【Conclusion】 The MmedOBP18 of M. mediator has strong binding capabilities to long-chain low volatile or non-volatile compounds. We speculated that MmedOBP18 may play a dual role in olfactory and taste recognition, and is mainly involved in the close range perception of chemical signals from host and host habitats.

Key words: Microplitis mediator, odorant binding protein, MmedOBP18, immunofluorescence localization, ligand binding characteristics, chemoreception