Two biopesticides Serratia marcescens [Eubacteriales:Enterobacteria] (used at MC 50 , concentration caused 50% malformation )and Bacillus thuringiensis Var. kurstaki (used at LC 50 ) and insect growth regulator Teflubenzuron (used at LC 50 value) were used for treatment of larvae of cotton leaf worm , Spodoptera littoralis (Boisd.) . Sequential combined Effect was carried out by treating 2 nd instar larvae with LC 50 value of B. thuringiensis or Teflubenzuron then the larvae allowed to pupate on sawdust treated with S. marcescens at MC 50 .The effect of these three agents were assessed by toxicity , fecundity , fertility , phosphatases activity and total carbohydrates . The obtained results revealed that Teflubenzuron is a potent toxin ( LC 50 = 0.113 ppm ) compared to B. thuringiensis ( LC 50 = 165.64 ppm ). On the other hand, the mode of action of S. marcescens is through malformation, the malformation concentration fifty (MC 50 ) is 3.09x10 8 colony forming unit/ml (cfu/ml) . All treatments caused a significant reduction in fecundity and fertility. The sequential combined effect showed more reducing effect on the fecundity and fertility than the individual treatments. Moreover, the activity of phosphatases and total carbohydrates were significantly fluctuated during the different periods of pupal stage. The sequential combined effect of Teflubenzuron with S.marcescence caused more significant effect on alkaline phosphatase activity than the individual treatment with S.marcescence but it was somewhat similar to Teflubenzuron. Also the sequential combined effect treatment of B. thureinginsis with S.marcescence had more effect than the individual treatment either with S.marcescence or B. thureinginsis. Moreover, all treatments caused significant decreases in total carbohydrates during the pupal stage and the sequential combined effect treatments had more decreasing effect than the individual treatments. According to the obtained result, S.marcescence could be considered as a biopesticide , and become more effective when used in sequential treatment with either Teflubenzuron or B. thuringiensis .

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The second instars S. littoralis larvae were exposed to the LC 50 of Teflubenzuron, Bacillus thuringiensis Var. kurstaki. , and the concentration (MC 50) of Serratia marcescens causes 50% malformation for pupae, separately and in sequential combined of both B. thuringiensis/ S.marcescens (Bt/Sm) and Teflubenzuron/S.marcescens to compare the effect of the tested pesticides on the aspartate aminotransferase (AST) activity and alanine aminotransferase (ALT) activity during pupal stage of Spodoptera littoralis Boisd. Treatment with B. thuringiensis or S. marcescens alone revealed generally significant decreases to AST through pupal stage relative to control. The highest levels of (AST) aspartate aminotransferase activities were clearly found in individual treatment with Teflubenzuron. On the other hand , when the sequential combined effect treatment B. thuringiensis/ S. marcescens (Bt/Sm) was used , there were more reduction in the AST activity at 2 nd , 4 th and 10 th days than that of S. marcescens and generally ,during the pupal stage, the sequential Bt/Sm had less effect than individual B. thuringiensis. The effect of Teflubenzuron / S. marcescens ((Teflu/Sm) commonly was higher than individual S. marcescens but less effective than Teflubenzuron alone. Also, Teflubenzuron had an effect on alanine aminotransferase (ALT) activity higher than B. thuringiensis which was effective than S.marcescence. In contrast, in the sequential combined effect treatments, Bt/Sm exhibited more decreasing effect at 2 nd , 12 th and 14 th day of pupation (-72.93% ,-82.86% and-89.56% , respectively) than treatment with B. thuringiensis alone. Teflu/Sm caused significant reduction in alanine aminotransferase activity except at 4 th and 6 th days, where there is significant increase. The increase at 6 th day (203.56%) was higher than that of Teflubenzuron alone (126.18%) or S. marcescens (47.60%). But overall, Teflubenzuron alone had the highest effect.

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