This study aims to characterise and test the bioactivity of nanoemulsion formulations based on essential oils from three plant species (Cymbopogon citratus, Citrus hystrix and Melaleuca cajuputi) as nano-pesticides in soya bean fields. The results showed that all formulations successfully formed stable, monodisperse nanoemulsions with droplet sizes ranging from 119±0.49 nm to 136±1.69 nm, a low polydispersity index (PDI) (0.22–0.24%), high transmittance (87.8–89.5%), and significant zeta potential values (±32.1 to ±37.9 mV). GC-MS analysis confirmed the efficiency of the nano-matrix encapsulation, as evidenced by the enrichment of the fractions of major volatile active compounds such as citronellal (57.08% in C. hystrix) and 1,8-cineole (46.87% in M. cajuputi). In bioassays, the Citrus hystrix formulation consistently demonstrated the best performance as a nanoinsecticide, with an LD₅₀ value of 3.31% and an optimum field application rate of 10 mL. Application of the formulation at a maximum dose of 15 mL/L reduced damage caused by pest infestation to the ‘Mild’ category, with minimal residual damage of 2.51–2.82%. This reduction in biotic stress significantly stimulated the recovery of vegetative growth (plant height reached 19.92–21.12 cm) and optimised yield components (total weight increased to 86.43 g in the C. hystrix treatment). This study demonstrates that the formulation of essential oil nanoinsecticides holds great potential as an effective plant protection agent for green crops