An urgent need exists for new agents to control mosquito vectors of disease. Mosquito larvicides based on the bacteria Bacillus thuringiensis subsp. israelensis (Bti) or B. sphaericus (Bs) are effective in many habitats, but use is limited by their high cost. Moreover, mosquito resistance evolves rapidly to Bs where it is used intensively. The efficacy of these bacteria is due to a binary protein (BsB) in Bs and four proteins (Cry4A, Cry4B, Cry11A, and Cyt1A) in Bti. Here we report the use of cyt1A promoters and a 5' mRNA stabilizing sequence to synthesize high levels of Bs2362 binary toxin in Bti strains. The recombinant BtiIPS-82/BsB showed high potency against fourth instars of Culex quinquefasciatus, a vector of West Nile virus, being 21-fold as potent as BtiIPS-82, and 32-fold as potent as Bs2362. Similar improved efficacy was obtained against larvae of Cx. tarsalis. Moreover, BtiIPS-82/BsB suppressed resistance to Bs2362 in Cx. quinquefasciatus.