Repellent efficacy of Coleus amboinicus Lour. (Lamiales: Lamiaceae) essential oil against Aedes aegypti L. (Diptera: Culicidae)

The increasing prevalence of mosquito-borne diseases such as dengue fever necessitates the development of effective and safe repellents. This study evaluated the repellent efficacy of Coleus amboinicus essential oil (CAEO) against Aedes aegypti, a primary vector of dengue in Malaysia. Essential oil was extracted via hydrodistillation and analyzed using GC-MS, revealing 17 compounds, with carbamic acid (30.75%) as the major constituent, followed by caryophyllene (6.52%) and ρ-cymene (6.40%). Repellency assays were conducted using human volunteers at concentrations of 2.5%, 5.0%, 10.0%, and 20.0% CAEO and DEET. Results indicated that CAEO exhibited a concentration-dependent repellent effect comparable to DEET, with 20% CAEO offering 95.83% repellency. Complete protection time evaluation showed CAEO provided 100% protection for 30 minutes and >80% efficacy for up to 3.5 hours, while DEET offered complete protection for 4 hours. The findings highlight CAEO's potential as a natural repellent alternative, although variability in composition and efficacy underscores the need for further research, including field trials and formulation enhancements to improve longevity and effectiveness.