Odorant-Binding Protein HvarOBP 5 in Ladybird Hippodamia variegata Regulates the Perception of Semiochemicals from Preys and Habitat Plants.

A total of 12 OBPs were identified in the antennae of ladybird Hippodamia variegata . HvarOBP 1/2/5/6/10/11 were highly expressed in adults, whereas HvarOBP 3/4/7/8/9/12 had higher expression levels in larvae. In adults, HvarOBP 1/2/4/5/6/7/8/11/12 were highly expressed in antennae. Among these, recombinant HvarOBP 5 strong bound with ( E )-β-farnesene (EβF), ( R )-(+)-limonene, ( E , E )-4,8,12-trimethyltrideca-l,3,7,11-tetraene (TMTT), ( E )-4,8-dimethyl-1,3,7-nonatriene (DMNT), hexyl hexanoate, and geranyl acetate. Molecular docking indicated that Leu42, Lys43, and His64 were the key binding sites of HvarOBP 5. All six ligands evoked electroantennography (EAG) responses in ladybirds. Moreover, ( R )-(+)-limonene and hexyl hexanoate were attractive to both sexes. After RNA interference for 72 h, the EAGs of dsRNA-injected ladybirds to DMNT and hexyl hexanoate were significantly decreased by 73.8 and 78.6%, respectively. Both dsRNA-injected males and females showed significantly lower behavioral preferences for DMNT and hexyl hexanoate. These findings suggest that HvarOBP 5 in H. variegata plays an important role in the perception of semiochemical cues from preys and habitat plants.