Acaricidal properties of Artemisia absinthium and Tanacetum vulgare (Asteraceae) essential oils obtained by three methods of extraction

Essential oils of Artemisia absindthium L. and Tanacetum vulgare L. were ex tracted by three methods, a microwave assisted process (MAP), distillation in water (DW) and direct steam distillation (DSD), and tested for their rel ative toxicity as contact acaricides to the twospotted spider mite, Tetrany chus urticae Koch. All three extracts of A. absinthium and of T. vulgare we re lethal to the spider mite but to variable degrees. The LC50 obtained fro m the DSD oil of A. absinthium was significantly lower (0.04 mg/cm(2)) than that of the MAP (0.13 mg/cm(2)) and DW (0.13 mg/cm(2)) oil of this plant s pecies. DSD and DW extracts of T. vulgare were more toxic (75.6 and 60.4% m ite mortality, respectively, at 4% concentration) to the spider mite than t he MAP extract (16.7% mite mortality 4% concentration). Chromatographic ana lysis indicated differences in composition between the more toxic DSD oil o f A. absinithium and the other two extracts of this plant, indicating that a sesquiterpene (C15H24) compound present in the DSD oil and absent in the other two may enhance the toxicity of the DSD oil. Chemical analysis of the T. vulgare extracts indicated that beta -thujone is by far the major compo und of the oil (>87.6%) and probably contributes significantly to the acari cidal activity of the oil.