Abstract
Spodoptera frugiperda is a major pest of maize that can causes severe yield losses, while intensive use of synthetic insecticides raises concerns about environmental contamination and food safety. This study evaluated the larvicidal toxicity, synergistic interaction, feeding inhibition, and egg-hatching inhibition of nanoemulsions formulated with Syzygium aromaticum and Myristica fragrans essential oils at ratios of 1:1, 2:1, and 1:2 (v/v). The nanoemulsions were prepared using a low-energy phase-inversion method with Tween 80 as the emulsifier. Larvicidal activity against third-instar S. frugiperda was evaluated using a contact bioassay at concentrations of 0, 0.125, 0.25, 0.50, 1.00, and 2.00% (v/v), and mortality was recorded for 96 hours after treatment (HAT). Larvicidal potency was estimated by probit analysis, while interactions between the essential oils were evaluated using the combination index (CI). Feeding inhibition and egg-hatching inhibition were also assessed at a total essential oil concentration of 1.00%. The 2:1 S. aromaticum: M. fragrans nanoemulsion exhibited the greatest larvicidal potency, with an LC50 of 0.10% and LC95 of 1.42% at 96 HAT, and showed strong synergism (CI = 0.26 at LC50). This formulation had a mean droplet size of 95.5 nm. At 1.00% total essential oil concentration, the 2:1 formulation inhibited egg hatching by 88% and reduced larval feeding, with the feeding inhibition index reaching 61.02%. These findings demonstrate the potential of the 2:1 S. aromaticum: M. fragrans nanoemulsion as a botanical insecticide candidate for the management of S. frugiperda. Further studies on chemical composition, formulation stability during storage, and efficacy under greenhouse and field conditions are needed to support its development as a botanical insecticide.