The effects of tree extractives, especially tree essential oils, on house-dust mites are reviewed. The essential oils contained in wooden flooring materials and sawdust from lumber used as building materials repressed mite reproduction. A comparison of mite control activity by tree species showed that the genera of Thuja and Eucalyptus had the greatest effect in stopping mite movement. The miticidal activity of vaporized essential oils was also studied and several potent essential oils and their components were found. In most cases, males were susceptible to essential oils than females and miticidal activity by the contact method was higher than that by the vapor method. Five of six Melaleuca species exhibited miticidal activity at the dosage of 1.3 x 10-4 mg/cm2, especially M. bracteata. The essential oil of Yaukusugi, a variety of Cryptomeria japonica, also exhibited strong miticidal activity. Cedrene, β-eudesmol, and cryptomerione were identified as the principal active compounds of Yakusugi. These results, as well as those of the leaf oils from Lauraceae, suggest that oxygenated sesquiterpenes greatly influence the behavior of mites. The miticidal activity of pisiferic acid and its congeners decreased in the order of the oxidized degree of the substituent at the 10 position of the abietane skeleton. The carboxylic group of pisiferic acid made a greater contribution to miticidal activity than did the phenol group. The wood oils of Thujopsis dorabrata var. hondae and Chamaecyparis taiwanensis suppressed population growth when added in concentrations of at least over 0.2% to culture media.
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