Toxicity of brown seaweed Sargassum wightii Greville (Sargassaceae) to the larval instars of vector mosquitoes Aedes aegypti Linnaeus, Anopheles stephensi Liston and Culex quinquefasciatus Say (Diptera: Culicidae)
摘要
Insecticidal activity of seaweeds against mosquitoes is underexplored compared to terrestrial flora. The present study was conducted to determine the toxicity of the brown seaweed Sargassum wightii extracts as an alternative to synthetic insecticides in managing vector mosquitoes. The crude solvent (petroleum ether, chloroform, acetone and methanol) extracts of S. wightii were tested for its toxicity on the second and third instar of Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus at concentrations of 100, 200, 300, 400 and 500 mg/L and larval mortality calculated 24 h after exposure. One hundred percent larval mortality was observed in the second instars of Ae. aegypti by the chloroform extract; in An. stephensi by chloroform and acetone extracts; and in Cx. quinquefasciatus by chloroform, acetone, and methanol extracts; and in the third instar of Cx. quinquefasciatus by the chloroform extract. Overall results indicated that the chloroform extract of S. wightii exhibited the maximum larval mortality at the lowest concentration against the second and third instars of Ae. aegypti, An. stephensi, Cx. quinquefasciatus, and their respective LC50 values were 158.39, 158.42, 178.94; and 189.48, 205.74, 190.40 mg/L. The chemical compounds present in the chloroform extract of S. wightii via GC–MS were toluene, methyl valerate, ethyl benzene, phenol,2,5-bis(1,1-dimethylethyl) and 4-amino-7-diethylamino-chromen-2-one. According to the existing literature survey, this is the first research report on the larvicidal activity by the chloroform extract of S. wightii, hence, larvicidal bioassays on the chemical components present in this extract is warranted.