Larvicidal Efficacy of Cola gigantea , Malacantha alnifolia and Croton zambesicus Extracts as Phytoinsecticides Against Malaria Vector Anopheles stephensi (Diptera: culicidae)

Malaria is transmitted by Anopheles stephensi and in controlling the malaria parasite Plasmodium spp., the vector mosquito has to be controlled. Extensive use of synthetic insecticides has resulted in environmental hazards and also in development of physiological resistance among vector mosquito species. Plant products are considered to be a potential alternative approach as they are environmentally safe, target specific and biodegradable. The n-hexane extracts of three plants viz ., leaves of Cola gigantea , Malacantha alnifolia and Croton zambesicus were evaluated against mosquito third instar larvae under ambient laboratory condition at Environmental Biology Laboratory, Department of Science Laboratory Technology, Rufus Giwa Polytechnic, Owo, Ondo State, Nigeria. The larvicidal effects of the three plant species were tested at the following dosages: 0ml; 2ml; 4ml and 5ml. Larval mortality toxicity was calculated after 24 hours exposure period and the results obtained show that all the extracts exerted varying significant (P<0.05) percentages of larvae mortality effect; extract of C. gigantea was found to have the highest mortality rate at LC 50 and LC 90 . From the phytochemical screening conducted on the plants, it was observed that the plants contain some secondary metabolites which are likely responsible for the larvicidal properties exhibited by the tested plants. The plants extracts show to be promising alternative to synthetic insecticides in malaria vector control programme and its adoption is advocated. Further studies need to be conducted to isolate and characterize the active molecules present in the plants.