Bacillus thuringiensis (Berliner) strains isolated from soil of citrus orchards were tested for insecticidal activity against the Mexican fruit fly, Anastrepha ludens (Loew), a key citrus pest in Mexico. From a total of 55 soil samples, 201 isolates were selected, for a total B. thuringiensis index of 0.66. The collection was characterized through light microscopy, polyacrylamide gel electrophoresis (SDS-PAGE), and PCR analysis detecting cry2, cry4, cry10, cry11, and cry19 genes. Of the 201 isolates, 51% produced ovoid crystals, 28% adhered to the spore, 15% were pleomorphic, 3% were bipyramidal, 2% cubic, and 1% was pyramidal type. Six colonies were positive for the cry10 gene and one for the cry19 gene. SDS-PAGE of spore-crystal preparations revealed seven electrophoresis patterns. These were bioassayed against Mexican fruit fly adults, obtaining maximum mortality of 28%.