Effects of mixture of orange peel essential oil with two chemical acaricides, spirodiclofen and propargite against adult females of Tetranychus urticae (Acari: Tetranychidae)

Recently, the use of plant essential oil as natural compound for protecting crops and decreasing environmental pollutions has been considered. In this study, contact and fumigant toxicity of peel essential oil of Citrus sinensis singly and in combination with spirodiclofen and propergite were evaluated against adult females of two-spotted spider mite, Tetranychus urticae. Median lethal concentration (LC50) values of essential oil of orange peel in the contact and fumigant toxicity assay, were 11.48 μg/cm2 and 48/75 μl/l air, respectively. Contact toxicity of C. sinensis essential oil in comparison with the two chemical compounds showed that T. urticae was more sensitive to spirodiclofen (LC50= 2.76 μg/cm2) than the essential oil, while propargite was less efficient (LC50= 28.51 μg/cm2). Furthermore, mixture of propargite and essential oil of orange peel (both at LC25) showed a mortality less than the total expected mortality (50 %). In contrast, mortality of LC25 of spirodiclofen mixed with C. sinensis essential oil was much higher than that of the total expected mortality (96.66 %). According to co-toxicity coefficient (CTC) factor, mixtures of C. sinensis essential oil with propargite and spirodiclofen, exhibited antagonistic and synergistic effects, respectively.