Acaricidal and repellent activity of plant essential oil-derived terpenes and the effect of binary mixtures against Tetranychus urticae Koch (Acari: Tetranychidae)

Realtionships between toxicity and repellent activity of plant essential oils and their major constituents to insects and mites remain unclear thus far. In the present study, the acaricidal and repellent activity of twenty terpenoid compounds commonly occurring in plant essential oils are evaluated against adults of the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Significant differences in toxicity were found for some compounds based on the application volume applied to leaf discs, and between bean and cabbage leaf discs. There was only a weak correlation between toxicity and repellent activity of the compounds. A lack of significant difference in evaporation of selected compounds, as determined by an ultra-fast gas chromatograph, failed to explain differences in toxicity between bean and cabbage leaves. Regarding repellent activity of binary mixtures of selected compounds, several synergistic and antagonistic interactions were observed, but no notable trend was apparent. Only vanillin significantly enhanced the repellency of all compounds tested including carvacrol, thymol, trans-cinnamaldehyde and α-terpineol.