S Rajkumar and A Jebanesan
Keywords: Chenopodium ambrosioides, Culex quinquefasciatus, Larvicide, ovicide, oviposition activity.
Abstract: Identification of novel effective secondary metabolites obtained from the plants can be used as an alternative to synthetic insecticides under the integrated vector control. The bioactivity of methanolic extract of the leaves of Chenopodium ambrosioides was studied under laboratory conditions for larvicidal, ovicidal and oviposition activity against Culex quinquefasciatus. The extract was the most potent in all activities and produced 50% larval mortality at 7.12 mg/l concentration. Clear dose - response relationships were established with the highest dose of 25 mg/l causing 100% mortality. In ovicidal activity, the egg rafts aged for 0-3, >3-6, >6-9, >9-12 and >12-15 h were individually exposed to different concentrations of extract ranging from 25 to 125 mg/l for 3 h. The results suggest that the ovicidal activity of the extract was influenced by concentration of the extract and age of the egg rafts. The effects of extract on the oviposition behaviour of Cx. quinquefasciatus was also evaluated in the present study. The concentrations of 100, 200, 300 and 400 mg/l reduced egg laying by gravid female mosquitoes from 27.7 to 90.2 %. The results of oviposition activity indicate that the extract exhibited oviposition deterrent activity against gravid female mosquitoes. The results obtained from this bioactivity study suggest that the leaf extract of C.ambrosioides is promising as mosquitoidal against Cx.quinquefasciaus and could be useful in the search for new natural mosquitocidal products in future
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