Essential oils of four plants (two species of lavender, peppermint, and a eucalyptus) and some of their principal constituents, i.e., linalool, linalyl acetate, fenchone, menthone, menthol, and eucalyptol, were tested in vitro for their acaricidal activity against Tyrophagus longior, a mite species that is a pest in stored food. Two different procedures were carried out to test the activity of these compounds by direct contact and by inhalation. In the direct contact assays five different quantities of each undiluted substance (6, 2, 1, 0.5, and 0.25 μl) were spread on the internal surface of 6-cm petri dishes, each containing 10 mites. The activity by inhalation was tested using two petri dishes of different sizes: the smaller one (6 cm), containing 10 mites, was covered with a filter-paper disk and enclosed in a bigger dish (9 cm) containing 6 oz 2 μl of each undiluted substance. At the highest doses, the essential oils of the two lavender species and of peppermint killed 100% of the mites, both by direct contact and by inhalation. Eucalyptus oil was the least active. Among the essential oil constituents, menthol showed the highest activity, killing 100% of the mites at the lowest dose (0.25 μl) by direct contact and at 6 μl by inhalation. However, linalool, fenchone, and menthone also showed good acaricidal activity. Eucalyptol, like the essential oil of which it is the principal constituent, had the lowest activity.

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