Repellence and insecticidal activity of Rhododendron anthopogonoides EO and head transcriptome analysis

Tribolium castaneum is a significant pest in grain storage, causing considerable economic impact globally. Plant-derived insecticides are being employed as alternatives to chemical insecticides and have shown strong insecticidal activity against T. castaneum. However, the mechanism underlying the insecticidal effects of plant-derived insecticides on T. castaneum remains unclear. In this study, we investigated the repellent, fumigation, and contact activities of R. anthopogonoides essential oil (EO) and its four main chemical components against T. castaneum. The results demonstrated that both the EO and its main chemical component, benzylacetone, exhibited potent insecticidal activity against T. castaneum. Benzylacetone may be the primary active component of R. anthopogonoides EO against T. castaneum. Subsequently, transcriptome sequencing of T. castaneum treated with Benzylacetone, along with negative controls, revealed 1616 differentially expressed genes (DEGs), with 758 up-regulated and 858 down-regulated genes. GO analysis indicated that the DEGs were mainly enriched in “cellular process,” “metabolic process,” “cell,” “cell part,” “catalytic activity,” “binding,” and other categories. KEGG pathway analysis revealed that the 417 DEGs were distributed across 217 different pathways, with several pathways related to xenobiotic or drug metabolism significantly enriched. This suggests that Benzylacetone likely disrupts metabolic and detoxication processes. Additionally, qRT-PCR validation of the TcOBP-4E and TcCYP450-6BK11 genes exhibited consistent results with the transcriptome data. Homology modeling and molecular docking results indicated the presence of a binding cavity formed by numerous hydrophobic amino acid residues in TcOBPs, with possible hydrogen bonds and hydrophobic interaction forces between the protein and ligand. These findings suggest that OBP and CYP450 play crucial roles in the resistance to foreign substances and provide a theoretical basis for understanding the insecticidal mechanisms of plant-derived insecticides at the molecular level.