FORMULATION AND CHARACTERIZATION OF NUTMEG ESSENTIAL OIL NANO EMULSION AND ITS BIO EFFICACY AGAINST RED FLOUR BEETLE TRIBOLIUM CASTANEUM

Abstract

Nutmeg essential oil (Myristica fragrans Houtt.) possesses promising bioactive properties and has attracted considerable interest as a natural insecticidal agent. In the present study, nutmeg oil nanoemulsions were formulated using Tween 80 as a non-ionic surfactant and distilled water as the aqueous phase. Three formulations with oil-to-surfactant ratios of 1:1 (NG T80 1:1), 2:1 (NG T80 2:1), and 3:1 (NG T80 3:1) were prepared through emulsification followed by ultrasonication. The physicochemical characteristics of the emulsions were evaluated using Dynamic Light Scattering (DLS), and their insecticidal efficacy was assessed against the red flour beetle, Tribolium castaneum, under laboratory conditions. DLS analysis confirmed the formation of nanosized droplets with average particle sizes of 56.80 nm, 157.8 nm, and 70.07 nm for NG T80 1:1, NG T80 2:1, and NG T80 3:1 formulations, respectively. The corresponding polydispersity index (PDI) values were 0.530, 0.391, and 0.648, indicating differences in droplet size distribution among the formulations. Contact toxicity bioassays were conducted at concentrations ranging from 1–10% (v/v), and mortality was recorded at 6,12, and 24 h after exposure. Mortality increased with both concentration and exposure period in all formulations. Among the prepared formulations, NG T80 2:1 exhibited the highest insecticidal efficacy at 6 h, with the lowest LC₅₀ value of 9.74%, followed by NG T80 3:1 with a value of  9.67%, whereas NG T80 1:1 required a higher concentration of 18.11% to achieve 50% mortality. After 12 h of exposure, all formulations were more effective, as evidenced by the reduction in LC₅₀ values. The NG T80 3:1formulation showed the greatest potency, with the lowest LC₅₀ 4.12%, followed by NG T80 2:1 with a value of 4.70% and NG T80 1:1 with LC 50 value of 5.40%. These findings demonstrate that prolonged exposure significantly enhanced the toxicity of the nano emulsions. At 24 h, all treated concentrations produced 100% mortality, indicating that exposure duration played a critical role in maximising insecticidal activity. The study highlights the potential of nutmeg oil nanoemulsions as eco-friendly botanical insecticide formulations for the management of stored-product pests.