The biopesticide Bacillus sphaericus represents one of the important tools used in the control of mosquito larvae after chemical insecticides. The present study was conducted to investigate the efficacy B. sphaericus 2362 (VectoLex) in two different technical powders, ABG-6232 and ABG-6491 against larvae of two mosquitoes, Culex pipiens and Aedes caspius in El-Arish city, North Sinai, Egypt. The mosquito larvae were collected from polluted and fresh water (Cx. pipiens) and saline water (Ae. caspius). The physicochemical characteristics of larval breeding water sites were measured as salinity, conductivity, pH values and temperature. Susceptibility bioassays showed that Cx. pipiens larvae from polluted water sites
have high susceptibility to B. sphaericus 2362 formulation ABG-6232 (LC50 0.15- 0.33 ppm, LC90: 0.73-9.68 ppm). In case of ABG-6491 formulation, the values were LC50: 0.15-0.33 ppm and LC90: 1.73-9.83 ppm. Cx. pipiens larvae collected from fresh water habitat in El-Qusiema, outside El-Arish city, susceptibility to B. sphaericus 2362 ABG-6232 had LC50 values ranging between 0.12 and 0.28 ppm, while LC90 ranged between 1.59 and 4.13 ppm. In case of ABG-6491, the LC50 values ranged between 0.13 and 0.28 ppm, while LC90 values ranged between 1.46 and 8.93 ppm. For Ae. caspius larvae from saline water and treated with B. sphaericus 2362 ABG-6232, LC50 values ranged between 0.31 &1.36 ppm, while LC90 ranged between 1.92 & 9.75 ppm. In case of ABG- 6491, the LC50 values ranged between 0.34 & 0.59 ppm, while LC90 values ranged between 1.79 and 11.56 ppm.