Larvicidal Activity of Solvent Extracts of Nicotiana tabacum L, and Datura metel L, (Solanales: Solanaceae) Against Larvae of Three Mosquito Species

Mosquitoes are insects that vector many of the life threatening diseases. Control of these insects is one of the major problems of the world today. Leaves and seed kernel extracts of Tobacco; Nicotiana tabacum (L.) and Thorn-Apple; Datura metel (L.) were assayed for larvicidal activity against three mosquito species of Aedes, Anopheles and Culex respectively. Samples of the three species were collected from mosquito breeding sites and reared in the laboratory for continued source of larvae following standard procedures. The plants parts used were extracted with hexane, chloroform and methanol in increasing order of polarity. Each extract was formulated into 0.9, 1.6, 2.4, 3.5 and 4.0mg/mL concentrations, and tested for larvicidal activity against 25 larvae of each genus in three replicates, alongside the controls over 12 to 72 hrs periods. The extracts that exhibited highest larvicidal activity were subjected to phytochemical screenings for searching active ingredients. Data were analyzed using Analysis of Variance, treatment means separated through DNMRT and lethal concentrations of the extracts were determined. Among the extracts tested, hexane extract of D. metel and methanol extract of N. tabacum caused highest larvicidal activity with more than 70% mortality on Aedes and Anopheles larvae when 4.0mg/mL was applied after 72 hrs (LC50 2.94±0.1 and LC502.58±0.1 mg/mL respectively). Culex larvae were less susceptible to all concentrations of the extracts. Though, larvicidal activity was observed to be directly proportional to concentrations and larval exposure periods, significant differences (p< 0.05) in the means of larval death were observed. The active extracts were found to contain alkaloids, saponins steroids, flavonoids and glycosides from moderate to high quantity which could be responsible for larvicidal activity. Future formulation studies, toxicity profile and possible mechanism of action may lead to the development of potential insecticidal products.