A novel encapsulation method for lemongrass essential oil in nanoemulsion and SiO2 nanoparticles against the storage mite Aleuroglyphus ovatus (Acari: Acaridae)

Abstract

Lemongrass essential oil (LEO), which is extracted from Cymbopogon citratus, has emerged as a promising alternative to traditional synthetic pesticides. In the present study, we fabricated pure LEO and its nanomaterials (nanoemulsion [NE] and SiO₂ nanoparticles [NPs]) and investigated their acaricidal effects on Aleuroglyphus ovatus (Acari: Acaridae), a common storage pest mite. A loading capacity (LC) of 57.45% was obtained, showing successful encapsulation of LEO in SiNPs. The contact mortality, fumigant mortality, ovicidal activity, repellent activity, and toxic effects of LEO on A. ovatus were investigated. The median lethal concentration (LC₅₀) values of contact mortality of LEO, LEO-NE, and LEO-SiNPs against adult mites were 0.067, 0.053, and 0.019 mg/cm², respectively, after 24 h of exposure. Similarly, the corresponding LC₅₀ values of fumigant activity were 0.044, 0.096, and 0.067 mg/cm³, respectively. All products had greater contact and fumigant effects on nymphs and larvae than they did on adults. After 5 days of exposure to the products, LEO-NE and LEO-SiNPs had greater inhibitory effects on hatching than did pure LEO. LEO-SiNPs exhibited a rapid and significant repellent effect at 3 h (82.22%) and were effective even after 24 h (35.56%), indicating their persistent and long-term acaricide activity. A study of toxicity symptom revealed two different manifestations of toxicity in mites after exposure to these products (knock-down type and immobilized type). Taken together, these findings suggest that LEO and its nanomaterials exhibit significant acaricidal activity against A. ovatus.