Chemical composition and Synergistic toxicity of four essential oils on Tetranychus urticae (Acari: Tetranychidae)

Problems associated with the use of pesticides have urged the need for biodegradable, environmentally and ecologically safe pesticides. Owing to the high heterogeneity and complex composition, binary combinations of plant derived-essential oils often exhibit increased insecticidal activity through synergistic interactions. The aims of the present study, therefore were to: 1) determine essential oil yield and chemical composition of Myrtus communis L. (Myrtaceae), Foeniculum vulgare Mill. (Apiaceae), Eucalyptus globulus Labill. (Myrtaceae) and Pistacia atlantica Desf. (Anacardiaceae) essential oils by gas chromatography–mass spectrometry (GC–MS) at two different phenological stages and 2) evaluate durability and 3) fumigant toxicity of above-mentioned essential oils and their binary combinations against two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) eggs and adults. The essential oils yields (w/w %) varied between 0.69% for M. communis at vegetative stage and 1.27% for F. vulgare at full flowering stage. At the full flowering stage, 23, 24, 34, and 17 components were identified in essential oils of P. atlanticae, E. globulus, M. communis and F. vulgare, respectively. Oxygenated monoterpenes and monoterpene hydrocarbons constituted the majority of chemical classes in essential oils of the studied plants. Among the oils tested, the most toxic essential oils against adults and eggs of T. urticae were M. communis (LC50= 3.95 μL L−1 air) and F. vulgare (LC50= 0.91 μL L−1 air), respectively. The LC50 values for the binary mixtures of the essential oils ranged between 0.75 to 3.23 μL L−1 and between 3.78 to 6.84 μL L−1, for T. urticae eggs and adults, respectively. Based on the synergistic factor and dose reduction index, the most promising binary mixtures to T. urticae eggs and adults was E. globulus EO: P. atlantica EO. The essential oils of M. communis, E. globulus, F. vulgare and P. atlantica caused 71%, 69%, 61% and 51% mortality at 3rd day exposure, respectively. No mortality was recorded on 9th day of exposure for all plant essential oils. Such this fast-initial release could reduce the toxicological effects expected to each essential oils. Overall it seems that essential oils of the above mentioned plants have the potential to be used in management of T. urticae in greenhouse conditions.