The odorant-binding proteins SfOBP23 and SfOBP24 facilitate the recognition of sugarcane volatile compounds by Spodoptera frugiperda larvae

The fall armyworm threatens the production of sugarcane in China. This study integrates behavioral assays, volatilomics, molecular biology, and protein biochemistry to investigate the olfactory basis of larval host selection. Three volatile compounds-caryophyllene, diisobutyl phthalate, and cis-3-hexenyl propionate-were identified from infested sugarcane plants via GC-MS. Behavioral bioassays revealed that diisobutyl phthalate and cis-3-hexenyl propionate significantly attracted larvae, while caryophyllene exhibited strong repellent activity. RT-qPCR screening identified two odorant-binding proteins, SfOBP23 and SfOBP24, which were highly upregulated in response to these volatiles. Fluorescence competitive binding assays demonstrated that SfOBP23 preferentially binds caryophyllene (Ki = 11.11 μM), whereas SfOBP24 shows higher affinity for cis-3-hexenyl propionate (Ki = 14.63 μM). Molecular docking further elucidated key residue interactions. RNA interference-mediated silencing of SfOBP23 and SfOBP24 significantly reduced larval olfactory preference, confirming their functional roles in chemoreception. These findings reveal the molecular basis of volatile-mediated host selection of S. frugiperda and identify promising target genes and semiochemicals for developing behavioral control strategies against this pest.