Objective  In this study, we cloned the odorant receptor gene (LdOR2) and determined the expression levels of this gene in developmental stages and different tissues of the Lymantria dispar and its behavioral response to CO₂ stress. The results will provide a theoretical basis for clarifying the olfactory response mechanism of the L. dispar under climate change.

  Method  The LdOR2 gene was cloned through transcriptome library screening, and its characteristics were analyzed by bioinformatics. The expression levels of LdOR2 gene in different developmental stages and tissues as well as in different CO₂ concentrations (397, 550 and 750 μL/L) were determined by real-time fluorescence quantitative PCR technology. In addition, RNA interference (RNAi) technology was used to study the behavioral responses of L. dispar adults silenced by LdOR2 at different CO₂ concentrations.

  Result  The open reading frame (ORF) of LdOR2 gene in L. dispar was 1 203 bp, encoding 400 amino acids. The molecular mass of the LdOR2 protein was 45.76 kDa and the theoretical isoelectric point was 8.22. The phylogenetic tree showed that the LdOR2 in L. dispar was closely related to MsepOR24 Mythimna separata and AdisOR21 in Athetis dissimilis, and clustered into one group. RT-qPCR results showed that LdOR2 was expressed at all developmental stages of the L. dispar, with the highest expression level in female pupae and the lowest expression levels in male adults. In different tissues of female and male adults, the expression levels in antennae were significantly higher than those in other tissues (P < 0.05), but showed no difference between the antennae of female and male. The expression of LdOR2 gene decreased under high CO₂ concentration. Compared with the control group, the expression of female antennae under 550 μL/L and 750 μL/L conditions decreased by 21% and 29% (P < 0.05), respectively, and the expression levels of antennae of male L. dispar adults decreased by 43% and 7% (P < 0.05). After LdOR2 gene silencing, the tendency of female and male L. dispar adults to eugenol and cis-3-hexene-1-ol was weakened, while the response rates of the L. dispar silencers to seven volatiles decreased under high CO₂ concentration.

  Conclusion  LdOR2 plays an important role in the odor recognition of L. dispar. The sensitivity of L. dispar to odor was affected by the expression levels of LdOR2 gene regulated by the changes of CO₂ concentration.