Conserved and Antenna-Biased Odorant Receptor in the Rape Stem Weevil <i>Ceutorhynchus asper</i> Tuned to Green Leaf Volatiles from Hosts

The rape stem weevil, <i>Ceutorhynchus asper</i> Roel. (Coleoptera: Curculionidae), is a severe pest of oilseed rape. Currently, little is known about the chemosensory functions of odorant receptors (ORs) in coleopterans such as <i>C. asper</i>. Here, the antennal and body transcriptomes of adult <i>C. asper</i> were sequenced and annotated. In total, 49 ORs were identified in <i>C. asper</i>, and transcriptome and quantitative polymerase chain reaction (qPCR) analyses showed that <i>CaspOR5</i> was antenna-biased. Phylogenetic analyses suggested that homologs of CaspOR5 were conserved among coleopterans. In single sensillum recordings of transgenic flies, CaspOR5 was found to be narrowly tuned to six green leaf volatiles (GLVs) of oilseed rape. Molecular docking indicated that active sites of CaspOR5 bound to GLVs were highly conserved. (<i>E</i>)-2-hexenol, 1-hexanol, and (<i>Z</i>)-3-hexenol were attractive for both sexes of <i>C. asper</i>, and (<i>E</i>)-2-hexenal was only attractive to male weevils. In conclusion, CaspOR5 can facilitate perception of GLVs, thereby playing crucial roles in host plant search and location of <i>C. asper</i>. Our investigation provides insights into the olfactory functions of the conserved CaspOR5 in Coleoptera and can facilitate future research on developing novel green strategies in management of related pest weevils.