Influence of Extraction Method on the Larvicidal Activity of Three Thai Medicinal Plants Against Aedes aegypti

Abstract

The growing burden of mosquito-borne diseases has increased interest in plant-based alternatives to synthetic larvicides. This study examined how extraction method affected the larvicidal activity of three commonly used Thai medicinal plants, kaffir lime (Citrus hystrix) peel, holy basil (Ocimum tenuiflorum) leaves, and citronella (Cymbopogon citratus) stems, against Aedes aegypti larvae. Aqueous extracts were prepared by grinding or boiling and tested at a concentration of 10% (v/v) under laboratory conditions. Second- to third-instar larvae were exposed to each treatment, with 20 larvae per replicate and three replicates per group. Mortality was recorded after 1, 5, 24, and 48 hours. Larvicidal activity differed clearly among plant species and extraction methods. Ground kaffir lime peel extract produced the strongest and fastest effect, causing complete larval mortality within 24 hours. Boiled kaffir lime peel and ground holy basil extracts also showed high activity, reaching approximately 98% mortality at 48 hours. Because control mortality reached 11.7% at 48 hours, mortality at this time point was adjusted using Abbott's formula. After correction, ground kaffir lime peel remained fully effective, while boiled kaffir lime peel and ground holy basil produced approximately 98% corrected mortality. The results show that extraction method plays an important role in the larvicidal performance of aqueous plant extracts. In particular, freshly ground kaffir lime peel appears to be a promising, low-cost botanical option for Aedes aegypti control. Further research should identify the active compounds, determine LC₅₀ and LC₉₀ values, assess effects on non-target organisms, and confirm effectiveness under field conditions.