Larvicidal and repellent properties of adansonia digitata against medically important human malarial vector mosquito anopheles stephensi (Diptera: Culicidae)

摘要

Background & objectives: Development of plant-based alternative compounds for mosquito control has gained importance now-a-days, in view of increasing resistance in mosquito vectors to existing insecticides. The larvicidal and repellent activities of benzene, chloroform, hexane and methanol leaf extracts of Indian medicinal plant, Adansonia digitata were investigated against malarial vector, Anopheles stephensi. Methods: In all, 25 III instar larvae of An. stephensi were exposed to various concentrations (30-180 mg/l) in the laboratory by using the standard protocol described by WHO (2005). The larvae were exposed for 24 h and mortalities were subjected to log-probit analysis. Repellent activity of crude leaf extract at the dosages of 2, 4 and 6 mg/cm 2 was evaluated in a net cage (45 × 30 × 45 cm) containing 100 blood starved female mosquitoes of An. stephensi using the protocol of WHO (1996). Results: Preliminary phytochemical analysis of A. digitata showed the presence of triterpenoids and saponins. The LC 50 and LC 90 values of hexane, benzene, chloroform, and methanol extracts of A. digitata against An. stephensi larvae in 24 h were 111.32, 97.13, 88.55, 78.18 and 178.63, 176.19, 168.14, 155.42 mg/l, respectively. The repellent activity of methanol extract was found to be most effective and at higher concentration of 6 mg/cm 2 benzene, chloroform hexane and methanol extracts provided 100% protection up to 150, 180, 120 and 210 min against An. stephensi, respectively. Conclusion: The preliminary study indicated that A. digitata showed larvicidal and repellent activities against An. stephensi and could be used for controlling mosquitoes. Further studies are indicated to purify the active compounds from these plants for developing larvicide and repellents.