Microencapsulation of nutmeg-melissa essential oil for enhanced stability and prolonged mosquito repellent efficacy

Mosquitoes, as primary vectors for diseases such as dengue fever, malaria, chikungunya, and Zika virus, pose a significant threat to global public health. Repellents are a principal strategy for preventing mosquito bites. While a nutmeg and melissa essential oil (EO) blend was previously identified as a highly potent spatial repellent, its practical application is severely limited by high volatility and short-lived efficacy. This study aimed to overcome this barrier by developing a stable, long-acting formulation using a scalable microencapsulation technology. Prior to formulation, GC-MS analysis confirmed that nutmeg EO was dominated by α‑pinene, limonene, and α‑terpineol, while melissa EO featured citral isomers alongside geraniol and citronellal. The nutmeg-melissa EO blend was then successfully encapsulated via complex coacervation, achieving both high encapsulation efficiency (93.3%) and yield (96.8%), indicating its economic feasibility for industrial production. The resulting microcapsules demonstrated significantly enhanced stability, effectively addressing the inherent volatility of EOs. Crucially, this translated into a dramatic extension of performance: while the unencapsulated EO lost its repellent effect rapidly, the microcapsule formulation maintained a potent repellent rate of over 75.0% against Aedes albopictus for 96 h at a dosage of 0.5 g. This work provides a viable pathway for converting this potent botanical blend into a stable, long-acting, and commercially viable biopesticide, demonstrating a valuable strategy for the value-added application of industrial crops in vector control.