The aim of present study is to investigate the potential larvicidal activity of aqueous extract from leaves of Citrullus colocynthis (Handal) selected indigenous plants, activity of the mosquitoes A. arabiensis (the main vector of malaria in Sudan) and C. quinquefasciatus (the main vector of Filariasis in Sudan). Laboratory experiments were conducted in the Department of Biology, Faculty of Education, University of Khartoum and Insectary of Health National Laboratory (ISTAC), during the period 2008-2011. The larvicidal activity of leaves aqueous extract of Citrullus colocynthis(Handal) were tested against the 2nd ,3rd and 4th instars larvae of A. arabiensis and C. quinquefasciatus. Twenty-five laboratory reared each of A.arabiensis and C.quinquefasciatus second, third and fourth instar larvae were exposed to a wide range of test concentration (2500, 5000, 10000, 15000, 20000, and 25000ppm) and a control using de-chlorinated tap water. Four replicates of each of the concentrations of plant water extract separately, were undertaken for each of the two mosquito species to find out the activity range of the extract of leaves of the tested plant. The larval mortality for each stage was determined at 48 hours and by using log GADARIF UNIVERSITY JOURNAL OF SCIENCE &ARTS VOLUME NO (4) 2 dosage–probit mortality analysis, regression line using computer software programs to determine the values of each of the lethal concentrations, 50% (LC50) and 90%( LC90). The larvae in the toxic aqueous extracts exhibited behavioral responses and intoxication symptoms that vary in degree according to the type and concentration of the extract. The current study revealed toxic and lethal effect doses of plant leaf extracts on larvae. The larvae of A.arabiensis were more susceptible than the larvae of C. quinquefasciatus to Citrullus colocynthis(Handal). In all cases the, 2nd instar was more susceptible to the effect of the extract than the 3rd instar and the latter was more susceptible than the 4th instar against the two species of mosquitoes. The current study revealed that plant leaves extracts have high efficacy in the control of A. arabiensis and C. quinquefasciatus. Consequently, these water extract can be induded in programs of biological control of mosquitoes after its effect on other aquatic organisms and its safety to man are tested.

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