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Efficacy of the methanol extracts from fruits without seeds, whole yellow ripe fruits and seeds of the plant Solanum xanthocarpum was evaluated against larvae of Anopheles culicifacies, Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus, the important vector mosquitoes prevalent in the and region. Experiments were carried out on late 3(rd), or early 4(th) instar larvae of these mosquitoes using standard WHO technique. 24 and 48 hrLC(50) and LC90 values along with their fiducial limits, regression equation, chisquare (x(2))/heterogeneity of the response have been determined by log probit regression analysis. The 24 hr LC50 values as observed for fruit without seeds, whole fruits and seeds after six months were 79.6, 91.7 and 131.7; 131.4, 186.9 and 95.6; 273.4, 290.9 and 377.6 and 384.9, 450.6 and 520.0 mgl(-1) for An. culicifacies, An. stephensi, Ae. aegypti and Cx, quinquefasciatus respectively. However the 24 hrLC(50) values for fresh yellow ripe fruits and seeds determined previously were 51.6 and 66.9; 52.2 and 73.7; 118.3 and 123.8 and 157.1 and 154.9 mgl(-1) for the above four vector species respectively showing that the efficacy was decreased two to three times more after six months of storage. The 24 hrLC(50) values were also determined after one year of storage for fruit without seeds, whole fruits and seeds. The values were 103.3, 120.1 and 195.7; 146.3, 224.3 and 251.2; 316.9, 336.5 and 426.2 and 393.0, 500.3 and 656.7 mgl(-1) as compared to the 24 hrLC(50) values of 47.4,51.6 and 66.9; 52.3,52.2 and 73.7; 108.0,118.3 and 123.8 and 141.1,157.1 and 154.9 mgl(-1) of all the three fresh preparations for the above four vector species respectively showing that the efficacy was further decreased after one year of storage. Further the extracts should be used when they have been prepared from the fresh plant parts instead of the old stored parts. Larvae of anophelines were found more susceptible as compared to culicine. HPLC and IR studies showed that active component might be present in the fruits and seeds of this plant species. The study would be of great importance while planning vector control strategy based on alternative plant derived insecticides.