The insecticidal activity of materials derived from the fruits of Piper nigrum against third instar larvae of Culex pipiens pallens, Aedes aegypti, and A. togoi was examined and compared with that of commercially available piperine, a known insecticidal compound from Piper species. The biologically active constituents of P. nigrum fruits were characterized as the isobutylamide alkaloids pellitorine, guineensine, pipercide, and retrofractamide A by spectroscopic analysis. Retrofractamide A was isolated from P. nigrum fruits as a new insecticidal principle. On the basis of 48-h LC(50) values, the compound most toxic to C. pipiens pallens larvae was pipercide (0.004 ppm) followed by retrofractamide A (0.028 ppm), guineensine (0.17 ppm), and pellitorine (0.86 ppm). Piperine (3.21 ppm) was least toxic. Against A. aegypti larvae, larvicidal activity was more pronounced in retrofractamide A (0.039 ppm) than in pipercide (0.1 ppm), guineensine (0.89 ppm), and pellitorine (0.92 ppm). Piperine (5.1 ppm) was relatively ineffective. Against A. togoi larvae, retrofractamide A (0.01 ppm) was much more effective, compared with pipercide (0.26 ppm), pellitorine (0.71 ppm), and guineensine (0.75 ppm). Again, very low activity was observed with piperine (4.6 ppm). Structure-activity relationships indicate that the N-isobutylamine moiety might play a crucial role in the larvicidal activity, but the methylenedioxyphenyl moiety does not appear essential for toxicity. Naturally occurring Piper fruit-derived compounds merit further study as potential mosquito larval control agents or as lead compounds.

Plant essential oils from 29 plant species were tested for their insecticidal activities against the Japanese termite, Reticulitermes speratus Kolbe, using a fumigation bioassay. Responses varied with plant material, exposure time, and concentration. Good insecticidal activity against the Japanese termite was achived with essential oils of Melaleuca dissitiflora, Melaleuca uncinata, Eucalyptus citriodora, Eucalyptus polybractea, Eucalyptus radiata, Eucalyptus dives, Eucalyptus globulus, Orixa japonica, Cinnamomum cassia, Allium cepa, Illicium verum, Evodia officinalis, Schizonepeta tenuifolia, Cacalia roborowskii, Juniperus chinensis var. horizontalis, Juniperus chinensis var. kaizuka, clove bud, and garlic applied at 7.6 microL/L of air. Over 90% mortality after 3 days was achieved with O. japonica essential oil at 3.5 microL/L of air. E. citriodora, C. cassia, A. cepa, I. verum, S. tenuifolia, C. roborowskii, clove bud, and garlic oils at 3.5 microL/L of air were highly toxic 1 day after treatment. At 2.0 microL/L of air concentration, essential oils of I. verum, C. roborowskik, S. tenuifolia, A. cepa, clove bud, and garlic gave 100% mortality within 2 days of treatment. Clove bud and garlic oils showed the most potent antitermitic activity among the plant essential oils. Garlic and clove bud oils produced 100% mortality at 0.5 microL/L of air, but this decreased to 42 and 67% after 3 days of treatment at 0.25 microL/L of air, respectively. Analysis by gas chromatography-mass spectrometry led to the identification of three major compounds from garlic oil and two from clove bud oils. These five compounds from two essential oils were tested individually for their insecticidal activities against Japanese termites. Responses varied with compound and dose. Diallyl trisulfide was the most toxic, followed by diallyl disulfide, eugenol, diallyl sulfide, and beta-caryophyllene. The essential oils described herein merit further study as potential fumigants for termite control.

Plant essential oils from 43 plant species were tested for their nematicidal activities against the pine wood nematode, Bursaphelenchus xylophilus. Responses varied with plant material and concentration. Good nematicidal activity against male, female and juvenile nematodes of B. xylophilus was achieved with essential oils of Cinnamomum verum, Leptospermum petersonii, Asiasarum sieboldi, Boswellia carterii, Pimenta racemosa, Cymbopogon citratus, Mentha spicata, clove and garlic. Garlic and cinnamon oils showed the most potent nematicidal activity among the plant essential oils. Analysis by gas chromatography-mass spectrometry led to identification of three major compounds from garlic and two from cinnamon oil. These five compounds from two essential oils were tested individually for their nematicidal activities against the pine wood nematode. Responses varied with compounds and dose. LC50 values of diallyl trisulphide, diallyl disulphide and cinnamyl acetate against juvenile nematode were 2.79, 37.06 and 32.81 μl−1, respectively. The essential oils described herein merit further study as potential nematicides against the pine wood nematode.

Commercial plant essential oils obtained from 11 Myrtaceae plant species were tested for their antifungal activity against Phytophthora cactorum, Cryponectria parasitica and Fusarium circinatum. Good antifungal activity against Phytophthora cactorum was achieved with the essential oil derived from Leptospermum petersonii at 28 × 10 −3 mg/ml air concentration. Inhibition rates of Eucalyptus citriodora and Melaleuca quinquenervia were 35.4% and 33.6% at 28 × 10 −3 mg/ml air concentration, respectively. In a test with C. parasitica, inhibition rates of E. citriodora and L. petersonii were 29.4% and 38.5%, respectively. Only L. petersonii essential oil showed antifungal activity against F. circinatum. Analysis by gas chromatography-mass spectrometry led to identification of 16, 15 and 12 compounds, respectively, in the oils of L. petersonii, M. quinquenervia and E. citriodora. The antifungal activity of the identified compounds was tested individually using standard or synthesized compounds. The inhibition rates of citronellol, neral, geraniol and geranial were 100% against P. cactorum at 28 × 10 −3 mg/ml air concentration. In a test with C. parasitica, the inhibition rates of neral and geranial were 61.7% and 68.9% at 28 × 10 −3 mg/ml air concentration.

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