Characterization of Cry Proteins in Native Strains of Bacillus thuringiensis and Activity against Anastrepha ludens

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%.