Chemical constituents from the aerial parts of Rhododendron thymifolium and its bioactivities against Tribolium castaneum, Lasioderma serricorne, and Ditylenchus destructor

This study investigated chemical compositions and biocidal activities from the aerial parts of Rhododendron thymifolium against Tribolium castaneum, Lasioderma serricorne, and Ditylenchus destructor. In total, 13 components were isolated from the aerial parts of R. thymifolium by chromatographic separation techniques. Based on the results of MS, ¹H NMR, and ¹³C NMR spectrometry, their structures were determined as ent-kaurane-16β-ol (1), pentacosane (2), undecanoic acid, ethyl ester (3), 1-Tridecanethiol (4), 1-Dodecanol (5), 4-Methyl-7-hydroxycoumarin (6), tertradecan-1-ol (7), apocynin (8), 3-Methoxy-4-methylbenzaldehyde (9), scopoletin (10), hyperin (11), quercetin (12), acetophenone (13). In addition, ent-kaurane-16β-ol (1) was isolated from R. thymifolium for the first time. Then, the insecticidal toxicities against T. castaneum, L. serricorne, and D. destructor. of compounds 1–13 were evaluated, and the results showed that apocynin (8) and acetophenone (13) exhibited obvious contact activity against the storage pests with LD₅₀ values of 6.46 and 8.72 μg/adult respectively. Acetophenone (13) showed excellent contact activity against D. destructor with LC₅₀ values of 0.08 mg/mL. The study clearly showed the active fractions from R. thymifolium have might potential to be developed into potential compounds on storage insect prevention.