Development and Characterization of Cymbopogon winterianus (Jowitt) Essential Oil-Based Nano-Emulsion for Larvicidal and Antifeedant Activity Against Spodoptera litura (Fab.) (Lepidoptera: Noctuidae)

Spodoptera litura (Fab.) is a serious cosmopolitan pest with extensive host range causing severe economic losses to agricultural and horticultural crops. The essential oil (EO) of citronella grass, Cymbopogon winterianus Jowitt, known for its repellent activity against many insects, is considered as source of potential bio-pesticides. In the present study, citronella oil was extracted from the leaves by hydro-distillation method and analysed for chemical constituents using gas chromatography coupled to mass spectrometry (GC–MS). The phytochemical profiling of the same revealed the presence of thirteen mono- and sesqui-terpenoids, the major compounds being citronellal (26.38%), trans geraniol (24.61%) and citronellol (13.80%). A stable and homogeneous oil in water (O/W) nano-emulsion of citronella essential oil with oil content (15%) and Tween 80 (5%) was formulated and characterised for average diameter and surface charge on its droplets using Dynamic Light Scattering (DLS). Transmission Electron Microscopy (TEM) revealed the formation of nanometric spherical droplets. In laboratory bioassays, mortality of S. litura larvae was 100% at 10.0 mg mL⁻¹ and 12.50 mg mL⁻¹ concentrations of citronella EO and its nano-emulsion, respectively. The LC₅₀ values were 5.52 mg mL⁻¹ on oil and 4.19 mg mL⁻¹ on nano-emulsion. Larval feeding on leaf discs treated with citronella EO and its nano-emulsion was significantly reduced (P < 0.05). The Antifeedant Index (AFI) values at 25.0 mg mL⁻¹ of citronella oil and its nano-emulsion were 33.78 and 51.83, respectively. Both citronella EO and its nano-emulsion are potential candidates for development of botanical insecticides to control S. litura.