CONTACT TOXICITY AND ANTIFEEDANT ACTIVITIES OF RHODODENDRON YUNNANENSE EXTRACTS AGAINST STORAGE DISEASE AND PESTS OF TRADITIONAL CHINESE MEDICINES

This study evaluated the contact-killing and anti-feeding activities of Yunnan Rhododendron (Rhododendron yunnanense) extracts and their isolated compounds against pests threatening stored traditional Chinese medicinal herbs. Extracts were prepared using methanol, 99% ethanol, petroleum ether, and deesterified methanol, followed by liquid-liquid extraction and chromatographic purification. Bioassays targeted Rhyzopertha dominica, Stegobium paniceum, and Ditylenchus dipsaci, with toxicity assessed via topical application and Tween 80 suspension methods, while anti-feeding activity was tested using flour-based assays. Key results showed that de-esterified methanol leaf extracts yielded the highest paste (31.25%), followed by 99% ethanol leaf extracts (30.58%). The 99% ethanol leaf extract exhibited the strongest contact-killing activity, with LD50 values of 15.76 μg/adult (R. dominica), 14.69 μg/adult (S. paniceum), and 0.74 mg/mL (D. dipsaci). Among isolated compounds, 4-methoxy-7-hydroxycoumarin demonstrated remarkable anti-feeding effects (75.24% refusal rate at 2.5 mg/mL), while apocynin showed potent contact toxicity (LD50 = 6.53 μg/adult for R. dominica). These findings highlight Yunnan Rhododendron. (R. yunnanense) as a promising source of natural insecticides for eco-friendly pest management in herbal storage. Further research should explore mechanistic pathways and field applicability.