Abstract: 【Aim】 This study aims to investigate the expression of the odor binding protein gene MmedOBP19 in the sensilla in legs of the braconid wasp Microplitis mediator and the ligand binding characteristics of recombinant MmedOBP19. 【Methods】 The ultrastructure of sensilla on the legs of female and male adults of M. mediator was observed by using scanning electron microscope. The in situ hybridization assays were conducted to explore the expression of MmedOBP19 in the forelegs of female adults of M. mediator. The fluorescence-based competitive binding assays were performed to measure the binding abilities of the recombinant MmedOBP19 to 86 candidate ligand compounds. 【Results】 There are three kinds of morphological sensilla on the legs of adult wasps, including sensilla trichodea, sensilla chaetica and sensilla basiconica, amongst which sensilla basiconica with two pores on the tip belong to taste sensilla. The in situ hybridization analysis showed that the expression of MmedOBP19 was concentrated at the base of the sensilla in tarsi of the foreleg. The results of fluorescence-based competitive binding assays revealed that the recombinant MmedOBP19 had strong affinities with non-volatile plant secondary metabolites, such as gossypol (Ki=2.32±0.17 μmol/L), berberine sulphate (Ki=4.86±1.81 μmol/L), quercetin (Ki=4.93±0.21 μmol/L), tannin (Ki=5.23±0.38 μmol/L), rutin (Ki=5.91±0.26 μmol/L) and quinine (Ki=6.05±0.51 μmol/L). In addition, MmedOBP19 could bind to octadecenoic acid (Ki=4.32±1.73 μmol/L) and linoleic acid (Ki=3.55±0.44 μmol/L), but had a weak binding ability with limonene (Ki=12.65±2.55 μmol/L). 【Conclusion】 Legs of M. mediator wasps might be involved in chemical communication behavior, and MmedOBP19 in the legs of M. mediator wasps may play major roles in taste perception.

Key words: Microplitis mediator, odorant binding protein, sensilla, ultrastructure, in situ hybridization, fluorescencebased competitive binding assay, chemoreception