TostOBP12 mediates the olfactory response to host volatiles in the parasitoid wasp Trichogramma ostriniae

Trichogramma wasps are widely utilized as critical biological control agents in agricultural systems. Its efficacy relies on detecting host-derived chemical cues, yet the key molecular determinants underlying this process remain elusive. Here, we demonstrate that the odorant-binding protein TostOBP12 is indispensable for the host-seeking behavior of T. ostriniae. Interspecific behavioral assays revealed that only T. ostriniae exhibited significantly enhanced parasitism driven by the host sex pheromone. TostOBP12 was identified as the most highly expressed OBP in female heads. Molecular docking and competitive binding assays confirmed its high and broad affinity for both sex pheromones ((Z)-12:14AC and (E)-12:14AC) and egg surface compounds. Crucially, RNAi-mediated silencing of TostOBP12 completely abolished the wasp's behavioral response to sex pheromones without affecting its development, confirming its essential in vivo function. Our findings reveal a key molecular sensor in a tritrophic interaction and provide a promising target for enhancing biocontrol efficacy.