Plant essential oils from 26 plant species were tested for their insecticidal activities against the Japanese termite, Reticulitermes speratus Kolbe, using a fumigation bioassay. Responses varied with source, exposure time, and concentration. Among the essential oils tested, strong insecticidal activity was observed with the essential oils of ajowan ( Trachyspermum ammi ), allspice ( Pimenta dioica ), caraway ( Carum carvi ), dill ( Anethum graveolens ), geranium ( Pelargonium graveolens ), and litsea ( Litsea cubeba ). The composition of six essential oils was identified by using gas chromatography-mass spectrometry. The compounds thus identified were tested individually for their insecticidal activities against Japanese termites. Responses varied in a dose-dependent manner for each compound. Phenol compounds exhibited the strongest insecticidal activity among the test compounds; furthermore, alcohol and aldehyde groups were more toxic than hydrocarbons. The essential oils and compounds described herein merit further study as potential fumigants for termite control.
This study evaluated the larvicidal activity of 20 plant essential oils and components from ajowan ( Trachyspermum ammi ) and Peru balsam ( Myroxylon pereira ) oils against the mosquito, Aedes aegypti . Of the 20 plant essential oils, ajowan and Peru balsam oils at 0.1 mg/mL exhibited 100 and 97.5% larval mortality, respectively. At this same concentration, the individual constituents, (+)-camphene, benzoic acid, thymol, carvacrol, benzyl benzonate, and benzyl trans-cinnamate, caused 100% mortality. The toxicity of blends of constituents identified in two active oils indicated that thymol and benzyl benzoate were major contributors to the larvicidal activity of the artificial blend. This study also tested the acute toxicity of these two active oils and their major constituents against the water flea, Daphnia magna . Peru balsam oil and benzyl trans-cinnamate were the most toxic to D. magna. Two days after the treatment, residues of ajowan and Peru balsalm oils in water were 36.2 and 85.1%, respectively. Less than 50% of benzyl trans-cinnamate and thymol were detected in the water at 2 days after treatment. The results show that the essential oils of ajowan and Peru balsam and some of their constituents have potential as botanical insecticides against Ae. aegypti mosquito larvae.
Nematicidal activity of aliphatic compounds was tested to determine a structure-activity relationship. There was a significant difference in nematicidal activity among functional groups. In a test with alkanols and 2E-alkenols, compounds with C(8)-C(11) chain length showed 100% nematicidal activity against pine wood nematode, Bursaphelenchus xylophilus , at 0.5 mg/mL concentration. C(6)-C(10) 2E-alkenals exhibited >95% nematicidal activity, but the other compounds with C(11)-C(14) chain length showed weak activity. Nematicidal activity of alkyl acetates with C(7)-C(11) chain length was strong. Compounds belonging to hydrocarbons, alkanals, and alkanoic acetates showed weak activity at 0.5 mg/mL concentration. Nematicidal activity of active compounds was determined at lower concentrations. At 0.25 mg/mL concentration, whole compounds except C(8) alkanol, C(8) 2E-alkenol, and C(7) alkanoic acid showed >80% nematicidal activity. C(9)-C(11) alkanols, C(10)-C(11) 2E-alkenols, C(8)-C(9) 2E-alkenals, and C(9)-C(10) alkanoic acids showed >80% nematicidal activity at 0.125 mg/mL concentration. Only C(11) alkanol exhibited strong nematicidal activity at 0.0625 mg/mL concentration, the lowest concentration that was tested.
Medicinal plant extracts from 27 plant species in 20 families were tested for their larvicidal activity against housefly, Musca domestica (L.). Responses varied with plant material and concentration. Among plant species tested, Phryma leptostachya var. asiatica showed 100% larvicidal activity against M. domestica at 10 mg/g concentration. Larvicidal activities of Atractylodes japonica, Saussurea lappa, Asiasarum sieboldi, and Gleditsia japonica var. koraiensis were 89.3%, 85.3%, 93.3%, and 96.6% at 10 mg/g concentration, respectively. Extracts of Prunus persica, Curcuma longa, and Paeonia moutan produced moderate activity. Larvicidal activity of other plant extracts was less than 50%. Among test plant species, P. leptostachya var. asiatica showed the most potent larvicidal activity. The active constituent of P. leptostachya var. asiatica roots was identified as the leptostachyol acetate by spectroscopic analysis. The LC(50) values of leptostachyol acetate against M. domestica larvae were 0.039 mg/g. Naturally occurring medicinal plant extracts and P. leptostachya var. asiatica root-derived compounds merit further study as potential housefly larval control agents or lead compounds.
Commercial essential oils from 29 plant species were tested for their nematicidal activity against the pine wood nematode, Bursaphelenchus xylophilus. Good nematicidal activity against B. xylophilus was achieved with essential oils of Gaultheria fragrantissima and Zanthoxylum alatum. GC-MS analysis of the corresponding oils led to the identification of two and ten major compounds, respectively. Four compounds, methyl salicylate, ethyl salicylate, methyl trans-cinnamate and ethyl trans-cinnamate, were tested individually for their nematicidal activities against the pine wood nematode. Methyl and ethyl salicylates showed strong nematicidal activity at concentration of 2.0 mg ml −1 . Concentrations of 1.0 mg ml −1 , as well as lower concentrations showed only minor effects. Another compound, methyl trans-cinnamate, showed 100% activity at concentrations of 0.0625-2.0 mg ml −1 . With ethyl trans-cinnamate, 100% mortality was observed at concentrations of 0.25-2.0 mg ml −1 . The essential oils and their components described herein merit further study as potential nematicides against the pine wood nematode.
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