Larvicidal effects of croton ( Codiaeum variegatum ) and Neem (A zadirachta indica ) aqueous extract against Culex mosquito

摘要

Botanicals are promising bio-pesticide against the control of malaria vector since they are safe, target- specific and biodegradable. This study evaluates the larvicidal activities of Neem (Azadirachta indica) and Croton (Codiaeum variegatum) leaf extracts on the larvae of Culex mosquito under ambient laboratory conditions (28 ± 2 o C, 75 ± 5% RH, 12L: 12D photoperiod) at the Department of Biology Laboratory. Fourth instar larvae of Culex mosquito were exposed to the extracts of Neem and Croton. Concentrations of the plant extracts tested were 0%, 50%, 25%, 12.5%, 6.25%, and 3.125% at exposure periods of 6, 12, 18, 24 and 36 hours. The result of the two extracts showed significantly varying level of larvae mortality effect. Culex mosquito larvae mortality increased significantly as the concentration of the plant extract and exposure period increased. There was no survival of Culex larvae for Croton concentration of 6.25% upward at 30h exposure. However, for Neem extract, no survivor occurs only at 36h. The LC 50 at 24h for Croton and Neem were 5.98g/ml (4.48 – 7.51%) and 57.32g/ml (24.72 – 89.9%) concentrations respectively. Croton showed higher mortality rate at each concentrations than Neem, thus, indicating Croton to be the most effective against Culex mosquito.