Some Selected Plant Essential Oils-Based Bio Acaricides and their Nano-Emulsions to Control, the Two Spotted Spider Mite, Tetranychus urticae (Koch)

The acaricidal potential of some eco-friendly plant-derived essential oils (EOs) against adult females of Tetranychus urticae Koch under laboratory-controlled conditions was assessed. Four essential oils of cumin (Cuminum cyminum), lemon grass (Cymbopogon citratus), clove (Syzygim aromaticum), and black pepper (Piper nigrum) were extracted using a hydro-distillation Clevenger-type apparatus. In-vitro leaf-dipping bioassay was assessed after one, two, and three days after exposure. Mortality varied according to the essential oil type, time of exposure, and the delivered dose (ppm). Clove EO was the most superior potent essential oil against adult females of T. urticae after 24 and 48 hours of exposure with LC50 values (417.68 and 247.82 ppm) but the last day cumin oil caused high mortality with LC50 value (173.62 ppm), followed by black pepper and lemon grass oils. GC-MS analysis of the most effective cumin and clove essential oils was performed and the most predominant compounds detected in clove EO were eugenol (44.66%), oleic acid (20.40 %), and eugenol acetate (15.36%), while for cumin EO were oleic acid (10.31%), p-Cumic aldehyde (10.24%), (-)-spathulenol (6.36%) and cumic acid (2.74%). Clove and cumin EOs-based nanoemulsions (NEs) with a high EO concentration (10%) and low Tween content were performed to minimize the volatilization and increase the acaricidal capacity. Of the nano-formulated NEs, clove NEs were the most effective after one day of exposure with an LC50 value of 60.55 ppm, but through the second and third days, cumin NEs were more effective than clove NEs with LC50 values of 39.89 and 16.36 ppm. Greenhouse experiments proved the effectiveness of the two nanoemulsions after spraying the candidate pest with their LC90 values on the eggplant plant. The reduction percentage for mites’ population was 99.38% for clove NEs and 99.20% for cumin NEs. The effect of clove and cumin EOs on some key enzymes anticipated the toxicity mode of action. Overall, clove and cumin essential oils and their nanophase proved their ability as bio-acaricides.