Contact toxicity and mechanisms of 4 compounds from Evodia rutaecarpa against Tribolium castaneum (Coleoptera: Tenebrionidae)

Tribolium castaneum causes significant damage to grains and their products. Increased resistance to synthetic insecticides poses a further challenge to pest control, highlighting botanical insecticides as an alternative. Evodia rutaecarpa is rich in anti-insect compounds and possesses insecticidal activity against T. castaneum. However, the underlying mechanism of action remains unclear. We evaluated the contact toxicity of 4 active compounds from E. rutaecarpa, linalool, caryophyllene oxide, α-terpineol, and rutaecarpine, against T. castaneum via topical application, and assessed their effects on neural and detoxification enzymes using spectrophotometry. α-Terpineol showed the highest contact toxicity, followed by rutaecarpine (LD50 = 63.42 μg/adult), linalool (LD50 = 74.07 μg/adult), and caryophyllene oxide (LD50 = 105.60 μg/adult). All 4 compounds affected key enzymes, with decreased AChE and increased GST activity. CES activity initially increased and then declined, suggesting neurotoxic disruption and detoxification induction. Transcriptomic and proteomic analyses were conducted to identify pathways affected by α-terpineol, indicating that the mechanism involves dysregulation of detoxification, neurotransmission, and developmental pathways, ultimately disrupting physiological and metabolic processes in T. castaneum. After cuticular penetration, α-terpineol activated detoxification genes (CYPs, ESTs, GSTs, and UGTs) and ATP-binding cassette transporters, while downregulating genes involved in cuticle formation (CHTs, CP63, Obstructor-B), energy metabolism (Treh), and neurotransmission (AChE). Molecular docking analysis revealed that the 4 compounds formed stable complexes with AChE, CES, and GST by hydrogen bonding, π-interactions, and hydrophobic contacts (binding energies ranged from -9.4 to -4.8 kcal/mol). Therefore, α-terpineol from E. rutaecarpa is a promising insecticide for controlling stored-product insects.