Three Host Plant Volatiles, Hexanal, Lauric Acid, and Tetradecane, are Detected by an Antenna-Biased Expressed Odorant Receptor 27 in the Dark Black Chafer Holotrichia parallela

Insects rely on olfaction to locate their host plants by antennae in complex chemical environments. Odorant receptor (OR) genes are thought to play a crucial role in the process. ORs function together with odorant coreceptors to determine the specificity and sensitivity of olfactory reception. The dark black chafer, Holotrichia parallela Motschulsky (Coleoptera: Scarabaeidae), is a destructive underground pest. To understand the molecular basis of H. parallela olfactory reception, an olfactory-biased expressed odorant receptor HparOR27 and HparOrco (HparOR40) were identified from antennal transcriptome analysis and prediction of the sequence structure. Tissue expression analysis showed that HparOR27 was mainly expressed in adult antennae throughout developmental stages. The functions of HparOR27 were analyzed using the Xenopus laevis oocyte expression system. HparOR27 was broadly responsive to three host plant volatiles, including hexanal, lauric acid, and tetradecane. Electroantennogram tests confirmed that three ligands were electrophysiologically active in antennae of female adults. A Y-tube olfactometer test indicated that hexanal was a repellent for adults of both sexes. Taken together, our data support the identification of odorant receptors and provide a molecular basis for eco-friendly pest control.