Leaf extracts of three native medicinal plants, damages the reproductive organs of the filarial vector, Culex quinquefasciatus Say (Diptera: Culicidae)

The limitations encountered with chemical insecticides to control mosquito borne diseases and proliferation of mosquitoes, has prompted the researchers to focus on developing insecticides of botanical origin. Acetone and methanol extracts of three medicinal plants were tested against the first instar of Culex quinquefasciatus and the lethal concentrations estimated. The column fractions of methanol extracts of the selected plants, Andrographis paniculata, Polyalthia longifolia and Bougainvillea spectabilis exhibited significant larvicidal activities. The 24 hr LC₅₀ of the methanol-ethyl acetate (MeOH-EA) 4:1column fractions of A. paniculata and P. longifolia and nHexane-ethyl acetate (nH:EA) 5:5 fraction of B. spectabilis are 3.013, 145.67 and 221.38 ppm, respectively. The effective concentration which affects 50% emergence (EC₅₀) of the treated larvae is 1.05 ppm, 72.6 ppm and 110.693 ppm respectively for the active column fractions. Total developmental duration and growth index were also affected by the column fractions. Exposure of the sub lethal dose affect the gonotrophic cycle of Cx. quinquefasciatus and also exhibited more than 90% control of reproduction in the tested group of treated males with untreated females (T♂ x UT♀) and exhibited higher sterility index. Dissection of the ovary and testes of Cx. quinquefasciatus after treatment with column fractions shows that the testicular development was drastically affected. The testes and ovaries of the treated mosquitoes showed variation in length and size and number of ovarioles when compared to control mosquitoes. The tested botanicals at comparatively lower dosages could effectively interfere with reproductive viability and check proliferation in next generation.