الفهرس 
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Abstract
In this study, the effect of the entomopathogenic bacteria Serratia marcescens used at minimal concentration caused 50% adult malformation ( MC50), Bacillus thuringiensis Var. kurstaki. used at LC50 and insect growth regulators Teflubenzuron used at LC50 on Spodoptera littoralis were studied. Also their sequential combined effect which carried out by treating 2nd instar larvae with LC50 values of B. thuringiensis or Teflubenzuron then the larvae allowed to pupate on sawdust treated with S. marcescens at MC50 were evaluated against Spodoptera littoralis. .The latent effects were investigated by some biological and biochemical parameters. The results are summarized as follows: Teflubenzuron is a potent toxin (LC50 = 0.113 ppm) compared to B. thuringiensis (LC50 = 165.64 ppm). On the other hand, the mode of action of S. marcescens is through malformation (MC50 = 3.09x108 cfu). All treatments either the sequential or the individual caused a significant decrease in pupation, adult emergence, adult longevity, fecundity and fertility, while, the pupal mortality and adult malformation were significantly increased. Both Teflubenzuron and S. marcescens were clearly more effective than B. thureinginsis. S. marcescens significantly increased the pupal weight, both individual Teflubenzuron and the sequential combined effect of Teflubenzuron with S. marcescens significantly decreased the pupal weight, whereas, B.thuringiensis exhibited insignificant decrease and the sequential combined effect of B. thureinginsis with S. marcescens had no effect. All treatments exhibited insignificant effect on pupal duration. Some morphogenetic effects were ecorded, however, these were clearly higher with the sequential treatments than the individual treatments. S. marcescens, Teflubenzuron and their sequential combined effect caused clearly high increases in the chitinase activity as compared to control. The acid and alkaline phosphatases, protease, amylase, invertase and trehalase activities were significantly changed through the pupal stage as compared to control. But, the total soluble carbohydrate, protein and lipid contents were significantly decreased through the pupal in which the effect of the sequential combined effect treatments was higher than the individual treatments. Finally it could be concluded that Serratia marcescens, B. thureinginsis and Teflubenzuron treated individually has the potentialities to reduce population density of S. littoralis , especially in case of both Serratia marcescens and Teflubenzuron , as well as their combined effect by the sequential treatments which have compact higher than the individual treatments to use them in combating the population of S.littoralis .Hoping that the obtained results may be of help in integrated pest management. Key words: Serratia marcescens, Bacillus thuringiensis Var. kurstaki., Teflubenzuron, Spodoptera littoralis, Biological and biochemical effects , Sequential combined effects.