Synergistic larvicidal action of Citrus limon (L.) Osbeck (Rutaceae) and Bacillus thuringiensis Berliner 1915 (Bacillaceae) against the dengue vector Aedes aegypti Linnaeus 1762 (Diptera: Culicidae)

Botanical and microbial insecticides are promising alternatives to synthetic pesticides for mosquito control because of lower toxicity to non-target organisms and their innate biodegradation ability. The present study was aimed to determine the synergistic larvicidal action of Citrus limon and Bacillus thuringiensis on the dengue vector Aedes aegypti. The crude methanolic leaf extract of Citrus limon and Bacillus thuringiensis were tested separately on the third instar larvae of Aedes aegypti at concentrations of 100, 200, 300, 400 and 500 mg/L and at 0.5, 1.0, 1.5, 2.0 and 2.5 mg/L respectively. Larval mortality was observed after 24 and 48 hours and the corresponding LC₅₀ values were 285.1 and 219.5 mg/L for Citrus limon and 1.9 and 1.4 mg/L for Bacillus thuringiensis respectively. The synergistic larvicidal action showed high mortality and its LC₅₀ values were 158.5 and 109.9 mg/L after 24 and 48 hours of exposure respectively. This synergistic interaction was due to the phytocompounds of Citrus limon and toxins from Bacillus thuringiensis which showed toxicity on the larvae of the dengue vector, Aedes aegypti. Hence, the exploitation of plant chemicals and microbial pesticides can be suggested for use in mosquito vector control program for the control of mosquito-transmitted diseases.