Sandfly, Phlebotomus papatasi (Diptera: Psychodidae) is the potential vector of leishmania in Egypt. In this study, an attempt was made to investigate the ultrastructure and histopathological alteration in the midgut of Phlebotomus papatasi post-treatment with methoprene (IGR) and B. sphaericus 6184 and 6446 using transmission electron micrographs (TEM).
                After 48 h, the TEM of the midgut treated with methoprene (IGR) showed sloughing of the periepithelial layer, and overgrowth of the brush border of the midgut wall. After 48 h post-treatment, B. sphaericus 6184 spores were discovered in the lumen and the bacterium began to enter the microvilli. Certain ultrastructural abnormalities were found in the midgut of treated P. papatasi larvae after 48 h of treatment with B. sphaericus 6446, the cytoplasm was distinguished by many vacuoles and a broken brush border. Using the light microscope, IGR-treated third instar larvae showed brush boundary overgrowth and multifocal disintegration of the midgut wall. Focused areas were sloughed and epithelial cells were dissociated from each other in larvae treated with B. sphaericus 6184. The 3^rd instar P. papatasi larvae treated with B. sphaericus 6446 showed clear alterations such as total epithelial cell degradation. These results demonstrated that B. sphaericus 6446 showed the best results and great effect on P. papatasi 3^rd instar larvae. More research is needed to establish the appropriate control strategies for the many leishmaniasis vectors in their various ecological environments.