Insecticidal efficacy of nanoemulsion containing Mentha longifolia essential oil against Ephestia kuehniella (Lepidoptera: Pyralidae)

In recent years, different formulations such as nanoemulsions have been widely used for the target delivery, and enhanced biological functions of pesticides combinations. In this study, contact toxicity of Mentha longifolia L. essential oil compared with its nanoemulsion on Ephestia kuehniella Zeller has been investigated. The experiments were conducted and executed at ۲۷ ± ۱ °C, and ۷۵ ± ۵% relative humidity under dark conditions. Chemical composition of this plant extract was also studied. The main constituents were pulegone (۲۸.۸۴%), ۱,۸-cineol (۱۹.۶%), p-menthan-۳-one-cis (۸.۲%), β-pinene (۶.۴۶%) and p-menthan-۳-one-trans (۵.۸۶%). Results indicated that the mortality rate of ۵th instar larva of E. kuehniella increased with rising concentrations (۱۰۰۰۰-۴۰۰۰۰ppm) for oil and (۸۰۰۰-۲۰۰۰۰ ppm) for nanoemulsion, respectively. The essential oil LC۵۰ was ۲۱۳۵۲ppm, while this value for nanoemulsion was ۱۴۰۶۸ppm. According to the results, nanoemulsion was more effective than essential oil. M. longifolia oil had lower durability and the ۵۰% persistent time (PT۵۰) was ۲.۳۹ day compared to the nanoemulsion (PT۵۰ = ۱۷.۱۳ day) in the highest concentration of essential oil. The nanoparticle size was ۱۴-۳۶ nanometers (nm) when the transmission electron microscope (TEM) was applied. The surface morphology of nanoemulsion was also studied by TEM. The average size of the particles was estimated ۲۳۴nm by using laser light scattering apparatus. The overall results of this study show that by using nanoemulsion formulation, the effect of essential oil contact toxicity and its durability increases. Hence, the nanoemulsion slow-release formulation may represent a new category of biopesticides and this should be considered in the integrated pest management program.