Antenna-Biased Odorant Receptor HvarOR25 in <i>Hippodamia variegata</i> Tuned to Allelochemicals from Hosts and Habitat Involved in Perceiving Preys

Abstract

Odorant receptors (ORs) of ladybird <i>Hippodamia variegata</i> play vital chemosensory roles in searching and locating preys. In the current study, 37 ORs were initially identified from the antennal transcriptome of <i>H. variegata</i>. The quantitative polymerase chain reaction demonstrated that several <i>HvarORs</i> including <i>HvarOR25</i> were specific or enriched in ladybird antennae. In two-electrode voltage clamp recordings, recombinant HvarOR25 was narrowly tuned to six chemical ligands including aphid-induced, aphid-derived, and plant-derived volatiles. In electroantennogram assays, all six volatiles elicited electrophysiological responses. Among the six volatiles, <i>cis</i>-3-hexenyl acetate, hexyl butyrate, hexyl hexanoate, and 3-methyl-3-buten-1-ol were attractive for both sexes of <i>H. variegata</i>. Additionally, molecular docking indicated that HvarOR25 was bound to all ligands with high binding affinities. Taken together, HvarOR25 facilitates perception of preys by recognizing relevant allelochemicals from hosts and habitat. Our findings provide valuable insights into understanding biological functions of HvarORs and help to develop a novel biocontrol strategy based on olfactory-active compounds.