Nor-seco-tremulane sesquiterpenoids from the endophyte fungus of Rhododendron capitatum: dual aphicidal and nematicidal activity with multi-target toxic mechanisms.

BACKGROUND: Plant pests such as Acyrthosiphon pisum and Bursaphelenchus xylophilus pose destructive threats to crops and pine forests globally. Widespread application of synthetic pesticides has caused pest resistance and ecological risks, creating an urgent demand for eco-friendly, pesticidal natural products. Endophytic fungi of medicinal plants serve as an untapped reservoir of bioactive natural metabolites, which are a promising resource for excavating novel natural insecticides. RESULTS: Twenty-three natural derivatives, including 12 tremulane sesquiterpenoids (1-12), were isolated from Preussia, an endophytic fungus of Rhododendron capitatum. Compounds 1-4 were previously undescribed, among which preutremutin E (1) represents the first naturally occurring tremulane carbon-degraded sesquiterpenoid. Their structures were elucidated by spectroscopic data analysis and electronic circular dichroism (ECD) calculations. All compounds were tested for their toxic activities against A. pisum and B. xylophilus, respectively. Compound 1 exhibited optimal dual pesticidal activity against A. pisum and B. xylophilus, with 72 h LC50 (50% Lethal Concentration) values of 74.8 and 65.6 μg mL-1, respectively. Mechanistic assays revealed that 1 inhibited acetylcholinesterase and disrupted detoxification homeostasis in aphids, while inducing ultrastructural deterioration, antioxidant suppression, energy depletion and protein loss in nematodes. Molecular docking suggested 1 tightly occupies the active pocket of glutathione S-transferase (GST) via dual hydrogen bonds and hydrophobic interactions, blocking the core detoxification function of GST. CONCLUSION: To our knowledge, the present work represents the first systematic report on secondary metabolites and insecticidal potential of endophytic fungi derived from R. capitatum. Notably, compound 1, characterized as a novel nor-seco-tremulane-type sesquiterpene, displays potential nematicidal and aphicidal activity via multi-target toxic pathways, indicating that endophytic fungi from R. capitatum serve as a promising and valuable resource for the exploration of innovative natural insecticides. © 2026 Society of Chemical Industry.