Chemical Composition and Insecticidal Properties of Essential Oil Obtained from Artemesia songarica Schrenk

Thin layer chromatography-direct bioautography for investigation of antibacterial activities of Artemisia sieversiana Ehrhart ex Willd. essential oil

The aim of the study was to characterise the chemical composition of the essential oil extracted from a Chinese traditional aromatic herb, Artemisia sieversiana Ehrhart ex Willd and investigate its antimicrobial activities against Staphylococcus aureus, the test bacterium, using thin-layer chromatography-direct bioautography (TLC-DB). Gas chromatography-mass spectrometry analysis showed that the essential oil was dominated by chamazulene (44.44%). Undeveloped TLC-DB enabled the measurement of zone of inhibition as valid as and more sensitive than the traditional agar diffusion method. The overall antimicrobial effect was weak at the tested concentration range and the antimicrobial strength did not exhibit concentration dependence. At high essential oil concentration (>1000μg/ml), size of zone of inhibition was all <7mm. Developed TLC-DB separated the components and visualised the inhibition of bacterial growth on the plate surface where the active antimicrobials were determined to be the minor components, hydroxylated terpenes, rather than the dominant component, chamazulene.

Identification of Terpenoid Compounds and Toxicity Assays of Essential Oil Microcapsules from Artemisia stechmanniana

Plant essential oils, as biological pesticides, have been reviewed from several perspectives and play a key role in chemical ecology. However, plant essential oils show rapid degradation and vulnerability during actual usage. In this study, we conducted a detailed analysis of the compounds present in the essential oils of A. stechmanniana using gas chromatography-mass spectrometry (GC-MS). The results showed seventeen terpenoid compounds in the A. stechmanniana oil, with four major terpenoid compounds, i.e., eucalyptol (15.84%), (+)-2-Bornanone (16.92%), 1-(1,2,3-Trimethyl-cyclopent-2-enyl)-ethanone (25.63%), and (-)-Spathulenol (16.38%), in addition to an amount of the other terpenoid compounds (25.26%). Indoor toxicity assays were used to evaluate the insecticidal activity of Artemisia stechmanniana essential oil against Aphis gossypii, Frankliniella occidentalis, and Bactericera gobica in Lycium barbarum. The LC₅₀/LD₅₀ values of A. stechmanniana essential oils against A. gossypii, F. occidentalis, and B. gobica were 5.39 mg/mL, 0.34 mg/L, and 1.40 μg/insect, respectively, all of which were highly efficient compared with azadirachtin essential oil. Interestingly, A. stechmanniana essential oil embedded in β-cyclodextrin (microencapsule) remained for only 21 days, whereas pure essential oils remained for only 5 days. A field efficacy assay with the A. stechmanniana microencapsule (AM) and doses at three concentrations was conducted in Lycium barbarum, revealing that the insecticidal activities of AM showed high efficiency, maintained a significant control efficacy at all concentrations tested, and remained for 21 days. Our study identified terpenoid compounds from untapped Artemisia plants and designed a novel method against pests using a new biopesticide on L. barbarum.

Insecticidal activities of the essential oil of Rhynchanthus beesianus rhizomes and its constituents against two species of grain storage insects

The aim of this research was to evaluate insecticidal activities of the essential oil of Rhynchanthus beesianus rhizomes against adults of Liposcelis entomophila and Tribolium castaneum. Gas chromatography-mass spectrometry analyses revealed the presence of 44 compounds with β-eudesmol (19.1%), elemol (8.1%), α-terpineol (8.0%), methyl eugenol (6.5%), and caryophyllene (4.8%) being the major constituents. Bioactivity-directed chromatographic separation of the oil led to the isolation of four constituents, elemol, β-eudesmol, methyl eugenol, and α-terpineol. The essential oil exhibited fumigant toxicity against the adults of L. entomophila and T. castaneum with LC₅₀ values of 0.57 and 4.96 mg/L air while the two isolates, methyl eugenol and α-terpineol possessed fumigant toxicity against the booklice (LC₅₀ = 0.15 and 0.48 mg/L air, respectively) and the beetles (LC₅₀ = 1.81 and 4.96 mg/L air, respectively). The oil also possessed contact toxicity against the booklice and the beetles with LD₅₀ values of 121.56 μg/cm² and 54.93 μg/adult, respectively, while the two isolates β-eudesmol and elemol showed contact toxicity against L. entomophila (LD₅₀ = 99.21 and 35.19 μg/cm², respectively) and T. castaneum (LD₅₀ = 35.26 and 8.89 μg/adult, respectively). The results indicate that the oil of R. beesianus rhizomes and its isolates have potential as a source for natural insecticides.