Study On The Active Components Of Two Rhododendron Plants Against Chinese Medicinal Materials Stored Pests

The antagonistic storage method has been used as one of traditional methods in the Chinese medicine conservation,which can effectively prevent and control storage pests to maintain Chinese medicinal materials,it played an important role in the storage of Chinese medicinal materials.In order to inherit and carry forward this traditional method of combating storage pests,this paper selects two Rhododendron species,namely Rhododendron przewalskii and Rhododendron rufum,they were the research objects.Sitophilus oryzae,Tribolium castanenum,Liposcelis bostrychophila,Lasioderma serricorne adults were the target insects to explore the insect-resistant active substances of the plant materials from genus Rhododendron.Here follows the main research results and achievements:1.Isolation and identification of chemical components.The volatile oils of two Rhododendron plants were extracted by steam distillation method.The composition of volatile oil was analyzed by gas chromatography-mass spectrometry（GC-MS）.The results were as follows:Nine chemical constituents were identified from the volatile oil of R.rufum,accounting for 98.06%of the total oil,Among them,myristicin was the most important chemical component,accounting for 79.72%.Other major terpenoids account for 14%of the total oil,such as Manoyl oxide（6.72%）,2,2,7,7-tetramethyltricyclo[6.2.1.01,6]undec-4-en-3-one（4.38%）,etc.30 chemical components were identified from R.przewalskii volatile oil,accounting for 84.94%of the total oil,of which4-（2,3,4,6-tetramethylphenyl）-3-butene-2-one was the main component,accounting for 27.74%,Bisabolol oxide II（10.39%）,Manoyl oxide（10.78%）.The volatile oil of R.rufum and R.przewalskii extract were systematically separated by column chromatography and Sephades LH-20.The structures of the compounds were identified by ESI-MS,¹H-NMR,¹³C-NMR,Myristicin was isolated from the volatile oil of R.rufum.14 compounds were isolated from the R.przewalskii sample,including:Morin-3-O-β-D-glucopyranoside,5,7,4’-OH-3’-OCH₃flavonoid-3–xylosid,methyl thyrsiflorin B acetate,friedelin,Hyperoside,Rhododendrin,isoquercitrin,Excoecarin R1 methyl ester,24-methylenecycloartanyl-2’E,4’Z-tetradecadienoate,2-methyl-1-butanol,quercitrin,menthol,quercetin,avicularine.Among them,the compound friedelin,Morin-3-O-β-D-glucopyranoside,5,7,4’-OH-3’-OCH₃flavonoid-3-xylosid,Rhododendrin,methyl thyrsiflorin B acetate,24-methylenecycloartanyl-2’E,4’Z-tetradecadienoate,were the first separation from R.przewalskii.2.Activity test.In this study,the repellent activity of the volatile oil of R.rufum was evaluated against three storage pests,T.castanenum,L.bostrychophila,S.oryzae.The results showed that the volatile oil of R.rufum had good repellent activity against these three kinds of insects.In particular,it showed strong repellent activity against L.bostrychophila at 2 hours and 4 hours,after 4 hours,the repellent grade of each concentration group was V,and the activity was higher than the positive control DEET;The volatile oil of R.rufum had good repellent activity against T.castanenum,after 4 hours,the repellent grades of T.castanenum were all above IV;The volatile oil of R.rufum showed strong repellent activity against S.oryzae only under high concentration conditions after4 hours.Myristicin,the main component in the volatile oil of R.rufum,had strong contact toxicity against S.oryzaea,and the LD₅₀was 6.13μg/adult,its contact activity was second only to the positive control pyrethrin(LD₅₀=5.27μg/adult).Myristicin had good repellent activity against T.castanenum under high concentration,and the repellent grade was V,the repellent activity for S.oryzae was not significant.The repellent activity of the volatile oil of R.przewalskii against three insects,T.castanenum,L.bostrychophila,L.serricorne were evaluated.The results were as follows:the volatile oil of R.przewalskii had good repellent activity and long-lasting effect against the insect T.castanenum,at 78.63,15.73,3.15,0.63n L/cm²concentrations,they all showed significant repellent effect,the repellent grade was V,at 0.13 n L/cm²concentration,the repellent grade was IV;Under the conditions of high concentrations,the repellent grade were V against L.bostrychophila;The repellent activity for L.serricorne was not significant.Four terpenoids were isolated from R.przewalskii:Excoecarin R1 methyl ester,24-methylenecycloartanyl-2’E,4’Z-tetradecadienoate,methyl thyrsiflorin B acetate,friedelin had strong antifeedant activity against T.castanenum,and its effects were better than the positive control drugs.Among them,at the lowest concentration of 25 ppm,the antifeedant rate was 95.46%.This article based on the ancient theory of antagonistic storage carried out research on the control of medicinal material storage pests by Rhododendron plants,and put forward a new idea for the research on the ecological control of medicinal materials storage pests.The research results provided experimental basis for inheriting and applying traditional protection methods of Chinese medicinal materials.