Odorant-Binding Protein 33 Mediates Detection of the Host-Associated Compounds in Spodoptera litura Larvae

Odorant-binding proteins (OBPs) are integral components of the insect olfactory system, assisting in the recognition of volatile chemical signals; their host recognition function makes them potential targets for the development of novel attractants. In this study, we identified Spodoptera litura OBP33 ( SlitOBP33 ) as being highly expressed in larval antennae, suggesting a potential role in olfactory perception. Through fluorescence binding assays and molecular docking, we identified four critical residues in SlitOBP33 for ligand interaction. To elucidate the in vivo function of SlitOBP33, we used a bacterial-expressed system to produce double-stranded RNA, achieving a 90.67% knockdown of the SlitOBP33 transcript levels in larval antennae. Subsequent behavioral assays demonstrate that silencing SlitOBP33 significantly impaired larval responsiveness to ( E )-2-hexenal and ( Z )-3-hexenol. Together, these findings demonstrate that SlitOBP33 mediates the olfactory-driven host location in the S. litura larvae in the development of species-specific attractants in integrated pest management.