The efficacy of four insecticides belonging to different groups, synthetic pyrethroid (lambdacyhalothrin), carbamate (Marshal), fungicide (Topas), and insect growth regulator (Neemrich) as well as their joint action was tested against 3rd larval instar of Culiseta longiareolata. Based on concentration mortality data LC50 and LC90 values, results obtained showed that LC50 values as observed were 0.09, 2.3, 9.0and 25.0 ppm for lambdacyhalothrin , Marshal, Neemrich, and Topas, respectively. The results showed that all mixtures consisted of a 1:1 (v/v) ratio of the LC25 of each compound indicated a potentiating effect. The highest potentiating effect was achieved by a mixture of co-toxicity factor equaled+100 (lambdacyhalothrin + Neemrich). The lowest potentiating effects were obtained from mixtures of Marshal + Topas and Topas+Neemrich (co-toxicity factor equaled+40) . The tested insecticides completely inhibited the emergence of adults till 0.0078,0.0625,0.25 and 1 ppm for lambdacyhalothrin , Marshal, Topas and Neemrich, respectively, and the emergence of adults was inversely proportional to the concentration.