Characteristics of AgifCSP9 and Its Potential Involvement in Host Location by Aphidius gifuensis (Hymenoptera: Braconidae)

Chemosensory proteins (CSPs) are a class of small soluble proteins traditionally considered to facilitate the recognition of chemical signals in insects. This study investigates the potential involvement of AgifCSP9 in host location and its response to host-related volatiles by RT-qPCR, ligand-binding assays, molecular docking, and dynamics simulations in A. gifuensis. Transcriptomic profiling revealed that AgifCSP9 is highly expressed in the legs, with significantly higher relative expression levels in females and larvae compared to other developmental stages. Fluorescence competitive binding assays further demonstrated that AgifCSP9 exhibits relatively strong binding affinities to multiple host-related volatiles, among which sabinene, (Z)-β-ocimene, and myrcene displayed the highest affinities for AgifCSP9. Molecular docking and dynamics simulation analyses indicated that specific amino acid residues (Val9, Leu14, Ile40, Leu44, Ile67, and Phe70) of AgifCSP9 are involved in binding to these particular ligands. Collectively, these findings suggest that AgifCSP9 is a potential candidate molecule involved in host location by A. gifuensis, offering a promising molecular target for behavior-based pest management aimed at optimizing biological control efficiency.