Antenna-Biased HvarOBP6 Coordinates Chemical Sense in Ladybug Hippodamia variegata to Aphid Alarm Pheromones and Habitat Plant Volatiles

Ladybug, Hippodamia variegata, preys on most aphids. Odorant-binding proteins (OBPs) play an important role for the detection of prey in ladybugs. In the present study, we found the antenna-biased HvarOBP6 was localized in the lymph of sensilla basiconica types II and III (Sb2, Sb3). In vitro, the recombinant HvarOBP6 showed strong binding affinities with (E)-β-farnesene (EβF), (R)-(+)-limonene, (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT), hexyl hexanoate, geranyl acetate, β-ionone, nerolidol, and decanal, which are aphid alarm pheromones and habitat plant volatiles. All eight strongly bound ligands evoked strong electroantennography (EAG) responses and behavioral preferences of H. variegata. RNA interference targeting HvarOBP5 retained partial HvarOBP6 and function, whereas HvarOBP6 knockdown concurrently silenced HvarOBP5, leading to significantly diminished EAG responses and behavioral preferences with these cues. These findings demonstrate that HvarOBP6 plays a pivotal role in detecting aphids and plant odorants, highlighting its potential as a target for manipulating natural enemy behavior to enhance biocontrol strategies.