Combined Effect of a Chitinase Producing Bacteria and Bacillus thuringiensis Against Musca domestica (Diptera: Muscidae) Larvae. Elham M. Salama 1 *, I.A. Ismail 2 and Abeer A. Khattab 3 1 Entomology Department, Faculty of Science, Benha University, P.O. Box 13518,Egypt. 2 Pests & Plant Protection Dept., National Research Centre, 33 rd El Buhouth St. P. code: 12622, Dokki, Giza, Egypt. 3 Botany Department, Faculty of Science, Benha University, P.O. Box 13518, Egypt. Abstract: In the current study we investigated the potential of Streptomyces griseus which is a chitinase producing bacteria for insect control as a bio-pesticide and its mixture with Bacillus thuringiensis as a different mode of action. This Streptomyces griseus was isolated from Elsulayel area, Saudi Arabia at 2011. Serial dilution technique was adopted to isolate the organism and was screened for its chitinolytic activity. The activity of chitinase extracted was determined using standard colloidal chitin as the reference control. The enzyme activities were found to be 0.12 μg/ml/minute for degradation of crab. Musca domestica L. (Diptera: Muscidae) larvae was tested in feeding, drinking and contacts toxicity methods with both Streptomyces griseus and Bacillus thuringiensis, either separately of in combination with each other. Reduction in the percentages of pupal and adult emergence was recorded for seven days after treatment by two doses of B. thuringiensis (5.0 and 1.0 mg/ L) and with suspensions containing approximately 5× 10 10 ml -1 of Streptomyces griseus. The chosen concentrations were 1, 0.5 & 0.1 μmg/ ml. Contact toxicity of the Streptomyces griseus was found very weak and no significant result in comparison with normal control except in younger instars only. The bacterium Bacillus thuringiensis proved to be a good candidate in controlling Musca domestica. Furthermore, treated extracts affected house fly larvae and resulted in reduction of adult stages. The number of tested larvae developed to pupae and adults was less than that of control group. The crude extract at concentration 9.5x10 4 mg/l completely inhibited development from larvae to pupae. The current study gives the attentions that the Streptomyces griseus, which is a chitinase producing bacteria is not promising to be used as a bio-control agent or as an additives to Bacillus thuringiensis in reduction of Musca domestica population in control managements strategy. The difference of significance was found 4% to 5% in larval mortality with the first and second larval instars. The larvae was not susceptible to be affected and may be immunology resistant to Streptomyces griseus, non-pathogenic. It is only act as biodegradation factor for chitin in nature but very weak to act in alive biological system. Key words: Musca, synanthropic fly species, bacterial control, Bacillus thuringiensis, Streptomyces griseus. International Journal of ChemTech Research CODEN(USA): IJCRGG, ISSN: 0974-4290, ISSN(Online):2455-9555 Vol.9, No.06 pp 131-141,2016