ACARICIDAL ACTIVITY OF SOME ESSENTIAL OILS AND THEIR CONSTITUENTS AGAINST TYROPHAGUS LONGIOR, A MITE OF STORED FOOD

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