Acaricidal activity of Melissa officinalis oil and its formulation on Tetranychus urticae and the predatory mite Neoseiulus californicus (Acari: Tetranychidae and Phytoseiidae)

The deterrent and toxicity effects of Melissa officinalis L. essential oil on Tetranychus urticae Koch were studied under laboratory conditions. Leaf discs treated with increasing concentrations of lemon balm oil showed high percentage of repellency (64–86%), respectively. The oviposition deterrent indices (ODI) of Melissa oil was ranged (74–94%) for T. urticae at concentration (0.3–1%). The direct contact application of M. officinalis oil proved to be the most toxic application on various stages of T. urticae compared to leaf dipping, fumigation and systemic applications. Oil formulation (Melissacide) was shown to be the effective one against T. urticae nymphs, females and eggs (LC50 = 0.03, 0.03 and 0.04%) compared to Melissa oil.The toxicity of M. officinalis oil and Melissacide by direct spray to females and eggs of the predatory mite Neoseiulus californicus (McGregor) was tested. The predator N. californicus is extremely less sensitive to Melissa oil and Melissacide than the pest T. urticae in the laboratory. When N. californicus was sprayed with (LC50 and LC90 values reported on T. urticae), females mortalities ranged between 8.5–13%, respectively. Melissacide is non-persistent in the environment due to its volatile nature. No phytotoxicity was observed in bean plant after four weeks of Melissacide treatment.Results obtained chemically from M. officinalis oil, may suggest that the higher percentage of benzene, 1(1,5dimethyl-4hexenyl)4methyl (= α-curcumene), caryophyllene oxide, ëCadinol and cedrene of the oil could be responsible for the toxic effect