Surface dispersion and efficacy evaluation of a biowaste-based microemulsion for environmentally safe mosquito control

Mosquito-borne diseases continue to pose a major global public health challenge, while the widespread use of synthetic larvicides has led to environmental contamination, non-target toxicity, and insecticide resistance. Although botanical essential oils have emerged as promising alternatives, their practical application is often restricted by high volatility, poor aqueous dispersion, and limited residual activity. To address these limitations, the present study developed a sustainable microemulsion using citronella oil, dillapiole oil, and liquid biodiesel waste (LBW) as a renewable formulation component to improve dispersion, stability, and larvicidal performance. Unlike previously reported botanical larvicides that primarily rely on conventional oils or synthetic solvents, this formulation utilizes LBW as a value-added carrier, providing a dual benefit of waste valorization and improved formulation performance. The developed microemulsions were characterized for droplet size, zeta potential, physicochemical stability, dispersion behaviour, and larvicidal efficacy. The optimized formulation remained stable after accelerated storage (54 ± 2 °C for 14 days), exhibiting negligible phase separation, pH 6.8, a mean particle size of approximately 10 nm, and a zeta potential of 55 mV. The biodiesel-based formulation rapidly dispersed over the water surface, achieving a coverage area of 572.56 cm 2 , nearly five times greater than that of the conventional formulation (113.10 cm 2 ). Among the developed formulations, ME VI showed the highest larvicidal activity, with LC 50 values of 32.6 ppm and 27.6 ppm after 24 and 48 h, respectively, comparable to a commercial larvicide (34.9 and 30.9 ppm). Environmental assessment demonstrated 0% mortality of Daphnia magna and biodegradable residues below 100 μg L −1 , indicating reduced environmental persistence compared with conventional larvicides. These findings demonstrate that integrating botanical essential oils with liquid biodiesel waste provides an effective and environmentally sustainable larvicidal formulation while promoting the beneficial utilization of biodiesel by-products for mosquito vector management.