Essential oils are promising candidates for the substitution of synthetic pesticides owing to their pesticidal and pest repellent features and also lower environmental side effects. Despite the pesticidal effects, the most of essential oils lose their effects against environmental conditions. Nanoformulation is a technique that may protect or improve the pesticidal efficiency of plant essential oils. The acaricidal effect of chitosan nanocapsules loaded with Achillea millefolium L. essential oil against adult Tetranychus urticae Koch is described. The loaded nanoparticles have spherical shape and average diameters between 85 and 145 nm depending on the pH used in the synthesis. During 24-h exposure, the LC50 values of fumigant toxicity for free EO and CS-TPP/EO fabricated at pH = 3.5, 4.5, and 5.5 were obtained 5.05, 18.90, 60.28, and 127.4 µL/L air, respectively. Additionally, by studying contact toxicity the LC50 values after 48-h exposure of T. urticae were determined to be 5.51, 4.23, 3.30, and 1.56 µL/cm2 for free EO and nanoparticles prepared at pH = 3.5, 4.5, and 5.5, respectively. Fumigant and contact lethality tests reveal the slow and persistent release of the Achillea millefolium L. essential oil, proving the effectiveness of chitosan nanoencapsulation in prolonging the acaricidal effect. The lethality performance is shown to be affected by the size of loaded chitosan nanoparticles. Overall, the results showed that nanoformulation of this essential oil saved its pesticidal property for longer time; thus, the technique may be used for improving essential oils efficiency in pest control.
