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Synergistic larvicidal efficacy of methanol extracts from yellow ripe fruits of Solanum xanthocarpum (Schrad and Wendl.) and red fruits of Withania somnifera (Dunal) (Fam. Solanaceae) was evaluated against late 3rd or early 4th stage larvae of Anopheles stephensi (Liston), Aedes aegypti (Linnaeus) and Culex quinquefasciatus (Say), using standard WHO technique. Experiments were carried out with methanol extracts of fruits of S. xanthocarpum (SX) (24hr LC50: 77.7, 121.6, 142.8) and W somnifera (WS) (108.4, 135.1, 1092.1 mg l(-1)) which revealed that extracts from S. xanthocarpum were more effective as compared to W somnifera with all the three mosquito species, respectively. For synergistic studies on An. stephensi six different binary pairs viz. WS:SX (1:1), WS:SX (1:2) and WS:SX (1:3); SX:WS (1:1), SX:WS (1:2) and SX:WS (1:3) were prepared and a dose response curve was established to determine the 24 and 48 hr LC50 and LC50 values, along with their 95% confidence limits, regression equation, chi-square (X-2))/ heterogeneity of response by log probit regression analysis. The 24 and 48hr LC50 values as determined for three binary pairs viz.WS:SX (1:1), WS:SX (1:2) and WS:SX (1:3) were 32.7, 30.6 and 22.2 and 22.9, 16.3 and 12.9 mg l(-1) while the values for other three pairs viz. SX:WS (1:1), SX:WS (1:2) and SX:WS (1:3) were 32.7, 47.5 and 63.8 and 22.9, 29.1 and 50.2 mg l(-1) respectively. From the results it is clear that An. stephensi was very much susceptible to the binary pair WS:SX (1:3) as compared to the binary pair SX:WS (1:3) or in other words, the efficacy went up with increase in proportion of S. xanthocarpum and went down with increase in proportion of W somnifera extract. Experiments were done by mixing different fractions viz. 1/2, 1/3, 1/4th of LC50 each of SX and WS and it was observed that synergistic effect was observed even up to 1/4th of LC50 of these two plant extracts. Synergistic Factor (SF) and Co-toxicity Coefficient (CTC) were also determined to show the antagonistic and synergistic effects. The study would be of great importance while formulating vector control strategy based on utilization of the most effective synergist pair.