Acaricidal activity of binary blends of essential oils and selected constituents against Tetranychus urticae in laboratory/greenhouse experiments and the impact on Neoseiulus californicus

The aim of this study was to test the effectiveness of essential oils form Piper aduncum, Melaleuca leucadendra and Schinus terebinthifolius and their blends by fumigation and residual contact on Tetranychus urticae and its natural enemy, Neoseiulus californicus. Bioassays were performed in a greenhouse with the best blend of the oils and compared to the individual oils and Vertimec® (positive control). The main constituents identified by GC–MS were dillapiole, (E)-nerolidol and limonene in the oils from P. aduncum (76.5%), M. leucadendra (87.3%) and S. terebinthifolius (unripe/ripe fruits, 42.5/34.1%). The P. aduncum and M. leucadendra oils were the most toxic to the pest. Among the blends, the greatest toxicity to T. urticae occurred by residual contact with the M. leucadendra + S. terebinthifolius ripe fruit blend (50/50). The evaluation of the effects on N. californicus showed the compatibility of the oils and blends with the predator mite for use in the integrated management of T. urticae. β-Caryophyllene was the most toxic, independent of the method used. Based on toxicities of 11 oil constituents, the structure–activity relationship of these compounds is also discussed. This study showed that the acaricidal effect of the Piper, Melaleuca and Schinus oils can easily be increased by the binary combination of these oils. The binary blend between the oils of the Melaleuca leaves and ripe Schinus fruit in the greenhouse was effective at controlling the mite after 72 h, exhibiting the same level of toxicity as that found for the positive control (Vertimec 18 EC).