β-cypermethrin and essential oils incorporated into a single nanoformulation: chemical and biological characterization

This work developed and evaluated the toxicological effects of single nanoemulsions (NEs) of peppermint or palmarosa essential oils (EO) combined with β-cypermethrin (CP) using ultrasound technique. For NEs formulation ultrasound parameters were: ultrasound power = 65 W, sonication time = 2 min and cycles = 30 on/20 off. The optimized active ingredients:surfactant ratio was 1:2. The NEs of peppermint EO combined with CP showed two peaks at 12.77 (33.4% intensity) and 299.1 nm (66.6% intensity) and polydisperse index (PDI) values of 1, while the NEs of palmarosa EO combined with CP had a size of 104.5 nm and their PDI value, 0.220. Both NEs were transparent and they were stable for 2 months. The insecticidal effect of these NEs (active ingredients:surfactant ratio was 1:2) were evaluated against T. castaneum and S. oryzae adults and Cx p. pipiens larvae. The NEs of peppermint EO combined with CP showed an enhancement of bioactivity of β-CP between 4.22 and 16 folds, while NEs of palmarosa EO + CP between 3.90 and 10.6 folds in all these insects. Moreover, both NEs demonstrated high insecticidal activity in all insect for 2 months, although slightly increase of particle size was detected. In this regard, the NEs elaborated in this work can be considered as highly promising formulation for the development of new insecticides.