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 27 ± 1 °C, and 75 ± 5% relative humidity under dark conditions. Chemical composition of this plant extract was also studied. The main constituents were pulegone (28.84%), 1,8-cineol (19.6%), p-menthan-3-one-cis (8.2%), β-pinene (6.46%) and p-menthan-3-one-trans (5.86%). Results indicated that the mortality rate of 5^th instar larva of E. kuehniella increased with rising concentrations (10000- 40000ppm) for oil and (8000-20000 ppm) for nanoemulsion, respectively. The essential oil LC_50 was 21352ppm, while this value for nanoemulsion was 14068ppm. According to the results, nanoemulsion was more effective than essential oil. M. longifolia oil had lower durability and the 50% persistent time (PT_50) was 2.39 day compared to the nanoemulsion (PT50 = 17.13 day) in the highest concentration of essential oil. The nanoparticle size was 14-36 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 234nm 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.