Fumigant toxicity of lemon eucalyptus oil constituents to acaricide-susceptible and acaricide-resistant Tetranychus urticae.

This study was aimed at assessing the fumigant toxicity of 14 essential oil constituents from lemon eucalyptus, Eucalyptus citriodora Hook, and another ten known compounds to females of acaricide-susceptible, chlorfenapyr-resistant, fenpropathrin-resistant, pyridaben-resistant and abamectin-resistant strains of Tetranychus urticae Koch. Menthol (LC(50) , 12.9 µg cm(-3) ) was the most toxic compound, followed by citronellyl acetate (16.8 µg cm(-3) ), against the susceptible females. High toxicity was also produced by β-citronellol, citral, geranyl acetate and eugenol (LC(50) , 21.7-24.6 µg cm(-3) ). The fumigant toxicity of these compounds was almost identical against females from either of the susceptible and resistant strains, indicating that the compounds and acaricides do not share a common mode of action or elicit cross-resistance. Global efforts to reduce the level of highly toxic synthetic acaricides in the agricultural environment justify further studies on materials derived from lemon eucalyptus oil, particularly menthol and citronellyl acetate, as potential acaricides for the control of acaricide-resistant T. urticae as fumigants with contact action.