Abstract: 【Aim】 To clone the odorant receptor (OR) gene HvarOR21 highly expressed in the antennae of the variegated lady beetle, Hippodamia variegata and clarify the ligand binding characteristics of HvarOR21, so as to provide a theoretical basis for revealing the recognition mechanism of the localization of prey habitats for H. variegata. 【Methods】 Based on the adult antennal transcriptome sequencing data and the identification results of odorant receptors of H. variegata, the cDNA sequence of HvarOR21 with a complete open reading frame (ORF) was cloned using PCR. Phylogenetic analysis and sequence analysis were used to study the classification and sequence structure characteristics of HvarOR21, respectively. Through the heterologous expression in Xenopus oocytes coupled with two-electrode voltage clamp recording, the electrophysiological responses of the recombinant HvarOR21 to 66 candidate odorant compounds were determined. Using homology modeling and molecular docking simulation analysis, the binding sites between HvarOR21 and decanal were predicted. 【Results】 The full-length cDNA sequence of HvarOR21 (GenBank accession no.: PP236119) of H. variegata was cloned and the deduced protein has seven transmembrane domains with an intracellular N-terminus and an extracellular C-terminus, which conforms to the typical structure of insect odorant receptors, belonging to the coleopteran OR group 5 subfamily. The recombinant HvarOR21 specifically tuned to decanal in a dose-dependent manner. HvarOR21 bound multiple amino acid residues with decanal through hydrophobic interactions and van der Waals forces, with the binding energy of －22.18 kJ/mol.【Conclusion】 Decanal is a volatile compound emitted from cotton plants infested by Aphis gossypii. HvarOR21 has a specific electrophysiological response to decanal with strong binding affinity, suggesting that HvarOR21 plays an important role in the localization of prey habitats for H. variegata.

Key words: Hippodamia variegata, odorant receptor, two-electrode voltage clamp, decanal, molecular docking