Odorant-Binding Protein 33 Mediates Detection of the Host-Associated Compounds in <i>Spodoptera litura</i> 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 <i>Spodoptera litura</i> OBP33 (<i>SlitOBP33</i>) 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 <i>SlitOBP33</i> for ligand interaction. To elucidate the in vivo function of <i>SlitOBP33</i>, we used a bacterial-expressed system to produce double-stranded RNA, achieving a 90.67% knockdown of the <i>SlitOBP33</i> transcript levels in larval antennae. Subsequent behavioral assays demonstrate that silencing <i>SlitOBP33</i> significantly impaired larval responsiveness to (<i>E</i>)-2-hexenal and (<i>Z</i>)-3-hexenol. Together, these findings demonstrate that <i>SlitOBP33</i> mediates the olfactory-driven host location in the <i>S. litura</i> larvae in the development of species-specific attractants in integrated pest management.