The screening for bioactive principles from several Chinese medicinal herbs showed that the essential oil of Cymbopogon distans aerial parts possessed strong repellency against the booklouse, Liposcelis bostrychophila , and the red flour beetle, Tribolium castaneum . A total of 36 components of the essential oil were identified by GC and GC-MS. trans-Geraniol (16.54%), (R)-citronellal (15.44%), (+)-citronellol (11.51%), and α-elemol (9.06%) were the main components of the essential oil followed by β-eudesmol (5.71%) and (+)-limonene (5.05%). From the essential oil, four monoterpenes were isolated by bioassay-guided fractionation. The compounds were identified as limonene, citronellol, citronellal, and trans-geraniol. Geraniol and citronellol were strongly repellent against the booklouse, L. bostrychophila, whereas citronellal and limonene exhibited weak repellency against the booklouse. Geraniol and citronellol exhibited comparable repellency against the booklouse relative to the positive control, DEET. Moreover, geraniol and citronellol exhibited stronger repellency against the red flour beetle than DEET, whereas the two other compounds showed the same level of repellency against the red flour beetle compared with DEET.

The aim of this research was to determine the chemical composition and nematicidal activity of essential oil of Agastache rugosa flowering aerial parts against the root knot nematode, Meloidogyne incognita, and to isolate and identify any nematicidal constituents from the essential oil. The essential oil of A. rugosa aerial parts was obtained by hydrodistillation and analyzed by GC-FID and GC-MS. A total of 37 components of the essential oil were identified, with the principal compounds being methyleugenol (50.51%), estragole (8.55%), and eugenol (7.54%), followed by thymol (3.62%), pulegone (2.56%), limonene (2.49%) and caryophyllene (2.38%). Based on bioactivity-guided fractionation, the three active constituents were isolated from the essential oil and identified as methyleugenol, estragole and eugenol. The essential oil of A. rugosa exhibited strong nematicidal activity against M. incognita, with a LC50 value of 47.3 μg/mL. The components eugenol (LC50 = 66.6 μg/mL) and methyleugenol (LC50 = 89.4 μg/mL) exhibited stronger nematicidal activity against M. incognita (LC50 = 185.9 μg/mL). The results indicate that the essential oil of A. rugosa aerial parts and its constituent compounds have potential for development into natural nematicides for control of the root knot nematode.

In recent years, uses of environment friendly and biodegradable natural insecticides of plant origin have received renewed attention as agents for vector control. During a screening program for new agrochemicals from Chinese medicinal herbs and local wild plants, the ethanol extract of Evodia rutaecarpa Hook f. et Thomas (Rutaceae) unripe fruits was found to possess larvicidal activity against the mosquitoes. The aim of this research was to determine larvicidal activity of the ethanol extract of E. rutaecarpa unripe fruits and the isolated constituents against the larvae of the Culicidae mosquito Aedes albopictus. The powder, 5 kg of the fruit material, was extracted with 30 l of 95 % ethanol, filtered, and evaporated to dryness in a rotary vacuum evaporator. The crude extract was then partitioned between methanol-water and n-hexane. The n-hexane fraction was evaporated off to given n-hexane extract. The aqueous layer was repartitioned with chloroform to provide chloroform extract after evaporation of the solvent. Further partitioning with ethyl acetate gave a residue after evaporation of the solvent. Bioactivity-directed chromatographic separation of chloroform extract on repeated silica gel columns led to the isolation of three alkaloids (evodiamine, rutaecarpine, and wuchuyuamide I) and two limonoids (evodol and limonin). The structures of the constituent compounds were elucidated based on high-resolution electron impact mass spectrometry and nuclear magnetic resonance. Evodiamine, rutaecarpine, and wuchuyuamide I exhibited strong larvicidal activity against the early fourth instar larvae of A. albopictus with LC(50) values of 12.51, 17.02, and 26.16 μg/ml, respectively. Limonin and evodol also possessed larvicidal activity against the Asian tiger mosquitoes with LC(50) values of 32.43 and 52.22 μg/ml, respectively, while the ethanol extract had a LC(50) value of 43.21 μg/ml. The results indicated that the ethanol extract of E. rutaecarpa and the five isolated constituents have a good potential as a source for natural larvicides.

In our screening program for insecticidal activity of the essential oils/extracts derived from some Chinese medicinal herbs and spices, garlic (Allium sativum L.) essential oil was found to possess strong insecticidal activity against overwintering adults of Cacopsylla chinensis Yang et Li (Hemiptera: Psyllidae). The commercial essential oil of A. sativum was analyzed by gas chromatography-mass spectrometry. Sixteen compounds, accounting for 97.44% of the total oil, were identified, and the main components of the essential oil of A. sativum were diallyl trisulfide (50.43%), diallyl disulfide (25.30%), diallyl sulfide (6.25%), diallyl tetrasulfide (4.03%), 1,2-dithiolane (3.12%), allyl methyl disulfide (3.07%), 1,3-dithiane (2.12%), and allyl methyl trisulfide (2.08%). The essential oil of A. sativum possessed contact toxicity against overwintering C. chinensis, with an LC50 value of 1.42 microg per adult. The two main constituent compounds, diallyl trisulfide and diallyl disulfide, exhibited strong acute toxicity against the overwintering C. chinensis, with LC50 values of 0.64 and 11.04 /g per adult, respectively.

A screening of several Chinese medicinal herbs for nematicidal properties showed that Arisaema erubescens (Wall.) Schott tubers possessed significant nematicidal activity against the root-knot nematode (Meloidogyne incognita). From the ethanol extract, two nematicidal flavone-C-glycosides were isolated by bioassay-guided fractionation. The compounds were identified as schaftoside and isoschaftoside on the basis of their phytochemical and spectral data. Schaftoside and isoschaftoside possessed strong nematicidal activity against M. incognita (LC50 = 114.66 μg/mL and 323.09 μg/mL, respectively) while the crude extract of A. erubescens exhibited nematicidal activity against the root-knot nematode with a LC50 value of 258.11 μg/mL.

Essential oil of Chinese medicinal herb,Chenopodium ambrosioidesaerial parts was found to possess nematicidal activity against the root-knot nematodes,Meloidogyne incognita. The essential oil ofC. ambrosioideswas obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 27 components of the essential oil were identified. The principal compounds inC. ambrosioidesessential oil were (Z)-ascaridole (27.27%),ρ-cymene (19.05%), isoascaridole (14.75%),α-pinene (6.33%) andα-terpinene (5.12%). Bioactivity-guided chromatographic separation of the essential oil on repeated silica gel columns led to isolate three volatile components ((Z)-ascaridole,ρ-cymene and isoascaridole) from the essential oil. The essential oil and (Z)-ascaridole exhibited strong nematicidal activity againstM. incognitawith LC50values of 49.55 μg/mL and 32.79 μg/mL, respectively.ρ-Cymene and isoascaridole also possessed nematicidal activity againstM. incognitawith LC50values of 435.89 μg/mL and 1323.51 μg/mL, respectively but weaker than the crude essential oil.

The aim of this research was to determine chemical composition and repellent and insecticidal activities of the essential oil of Kaempferia galanga L. rhizomes against the booklouse, Liposcelis bostrychophila Badonnel, and to isolate insecticidal or repellent constituents from the oil. The essential oil was obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry. Twenty-eight components of the oil were identified. The major compounds in the oil were ethyl-rho-methoxycinnamate (38.6%), ethyl cinnamate (23.2%), 1,8-cineole (11.5%), trans-cinnamaldehyde (5.3%), and borneol (5.2%). Based on bioactivity-guided fractionation, four active constituents were isolated from the oil and identified as 1,8-cineole, ethyl cinnamate, ethyl rho-methoxycinnamate, and trans-cinnamaldehyde. The essential oil exhibited contact toxicity against the booklouse with an LC50 value of 68.6 microg/cm2. Ethyl cinnamate (LC50 = 21.4 microg/cm2) exhibited stronger contact toxicity than ethyl rho-methoxycinnamate and trans-cinnamaldehyde (LC50 = 44.6 and 43.4 microg/cm2, respectively) while 1,8-cineole showed weak acute toxicity. The essential oil also possessed fumigant toxicity against the booklouse with a LC50 value of 1.5 mg/liter air. 1,8-Cineole and trans-cinnamaldehyde (LC50 = 1.1 and 1.3 mg/liter, respectively) possessed stronger fumigant toxicity against the booklouse than ethyl cinnamate and ethyl rho-methoxycinnamate (LC50 = 10.2 and 10.2 mg/liter air, respectively). trans-Cinnamaldehyde was strongly repellent to booklice, whereas ethyl cinnamate and ethyl rho-methoxycinnamate were weakly repellent and 1,8-cineole did not repel booklice. The results indicate that the essential oil and its constituent compounds have potential for development into natural insecticides or fumigants and repellents for control of insects in stored grains.

The aim of this study was to evaluate the larvicidal activity of the essential oil of Youngia japonica aerial parts against the larvae of Aedes albopictus and to isolate any active compounds from the oil. Gas chromatography-mass spectrometry (GC-MS) analyses revealed the presence of 31 compounds, with menthol (23.53%), α-asarone (21.54%), 1,8-cineole (5.36%), and caryophyllene (4.45%) as the major constituents. Bioactivity-directed chromatographic separation of the oil led to the isolation of menthol and α-asarone as active compounds. The essential oil of Y. japonica exhibited larvicidal activity against the fourth instar larvae of A. albopictus with an LC₅₀ value of 32.45 μg/mL. α-Asarone and menthol possessed larvicidal activity against the fourth instar larvae of A. albopictus with LC₅₀ values of 24.56 μg/mL and 77.97 μg/mL, respectively. The results indicate that the essential oil of Y. japonica aerial parts and the two constituents can be potential sources of natural larvicides.