Comparative larvicidal activity of different species of Ocimum against Culex quinquefasciatus.

Ocimum is a genus of aromatic herbs, undershurbs or shrubs distributed in the tropical and warm temperate regions of the world. Larvicidal activity of essential oils and different extracts of O. sanctum, O. basilicum and O. gratissimum were compared on laboratory reared and field collected larvae of Culex quinquefasciatus. Thin layer chromatographic analysis revealed that all the three species have similar components and results showed the presence of steroids and triterpenoids. The larvicidal activity was determined in terms of LD₅₀ value on late third or early fourth instar larvae for a period of 24 h. A comparison of LD₅₀ value has shown that O. basilicum is more active than the other two species. The LD₅₀ value of O. basilicum and O. sanctum oil were 39.31 and 40.02 on laboratory reared larvae and 129.53 and 139.49 on field collected larvae. Laboratory reared larvae were more sensitive than field collected larvae.