Extension of the larval chemosensory gene repertoire uncovers stage-specific odorant receptors exhibiting convergent functional roles in Spodoptera littoralis

Chemical cues play a critical role in driving key insect behaviors and their detection is mediated by proteins such as binding proteins and chemosensory receptors. While holometabolous insects exhibit distinct morphologies, physiologies and ecologies across developmental stages, most research on chemical detection has focused on adults. Here, we analyze the larval chemosensory transcriptome of the polyphagous moth Spodoptera littoralis, the life stage responsible for plant damage. We identified expression of 39 previously unreported chemosensory genes, substantially expanding the known larval repertoire. Functional analyses of larval odorant receptors (ORs) revealed two receptors responding to terpenes and aromatic compounds emitted by host plants, and behavioral assays indicated that some of these ligands elicited attraction, demonstrating ecological relevance. A larval OR response profile perfectly mirrored that of an unrelated OR expressed in adults, suggesting that these two ORs converged on similar function in larvae and adults. Our results highlight stage-specific chemosensory equipment and identify promising targets for modifying larval behavior, with potential applications for improved insect control.