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  • Author or Editor: A. M. Refaat x
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The deterrent and toxic effect of two essential oils, Majorana hortensis. Moench and Rosma- rinus officinalis L. on the two tetranychid mites Tetranychus urticae Koch and Eutetranychus orientalis (Klein) were studied under laboratory conditions. Both materials used were more potent for E. orientalis than against T. urticae with a significant increase in repellency. Leaf discs treated with increasing concentrations of the two oils showed increased mortality of both spider mites and reduction in the total numbers of eggs laid. This result could be due to the oil of the higher oxygenated compounds content that was more effective in this respect.

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The deterrent and toxicity effects of mint, Mentha virdis L. and peppermint, Mentha piperita L. on Tetranychus urticae Koch were studied under laboratory conditions. M. virdis was more potent for T. urticae than M. piperita, with a significant increase in repellency. Leaf discs treated with increasing concentrations of both materials showed reduction in the total numbers of eggs laid. A high percentage of T. urticae mortality was recorded in case of M. virdis. The direct toxicity of both essential oils to the female of the predacious mites namely Typhlodromus athiase Porath and Swirski Phytoseius finitimus Ribaga, Amblyseius barkeri (Hughes), Amblyseius zaheri Yousef and El-Borolossy, Amblyseius yousefi Zaher and El-Borolossy and Amblyseius deleoni (Muma and Denmark) were tested. At LC 50 level, M. virdis was the most toxic to females A. yousefi and the least to females T. athiasae. With the exception of A. zaheri, M. piperita proved to be more toxic to the predacious mites tested than M. virdis. The results obtained chemically and biologically, may suggest that the higher percentage of the hydrocarbons of M. virdis were responsible for the toxic effect.

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Two essential oils, namely Ocimum basilicum L. and Lavandula offi­ci­nalis Chaix, were tested for their repellency, toxicity and oviposition deterrence against two tetranychid mites, tetranychus urticae (Koch) and Eutetranychus orientalis (Klein). Fifty-seven and forty-seven compounds, comprising about 96.7 and 95.4% of sweet basil and French lavender oil, respectively, were positively identified using GC-MS technique. Oil analysis revealed the dominant occurrence of the oxygenated terpenes in either oils (91.172 and 64.317%), respectively. The essential oil of French lavender was more potent for E. orientalis than against T. urticae. The ODI of both oils was ranged between (100-80) for both mite species at conc. (2- 0.5%). For both oils, a significant reduction in the total number of eggs laid by both tetranychid species was recorded at all con­centrations used. A high percentage of E. orientalis mortality was recorded for both materials while oil of sweet basil was more effective than French lavender oil in case of T. urticae. The results obtained chemically and biologically may suggest that the dominant occurrence of the oxygenated hydrocarbon compounds (91.172% of oil content) in sweet basil were responsible for the toxic effect.

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