Polylactic acid nanofibers encapsulating the insecticide fenobucarb were fabricated by coaxial electrospinning and evaluated for structure, release, and field efficacy in rice. The nanofibers showed an average diameter of 582.12 ± 108.49 nm with 47.175% fenobucarb loaded. In vitro, fenobucarb release reached 22.78% at day 5 and 43.19% at day 15, fitting the Korsmeyer Peppas model (n = 0.6014), indicating both profenofos diffusion and the swelling of the polylactic acid shell. Three formulations suspension concentrate, wettable powder, and granule were prepared from the nanofibers scaffolds and applied at 250 g a.i. ha⁻¹ in Bac Giang province, Vietnam. No phytotoxicity was detected. Both suspension concentrate and wettable powder reduced brown planthopper densities from 27 insects hill⁻¹ to 4.3 - 4.5 insects hill⁻¹ by 15 days after treatment, with efficacy of 86.1  86.8%, outperforming the commercial reference Bassa 50 EC (64.9%). Granule exhibited slower onset but extended activity. Compared with conventional formulations, polylactic acid encapsulation enhanced persistence and bioefficacy, suggesting a practical strategy to lower insecticide input and environmental exposure in rice ecosystems.