Isolation and Characterization of Different Bacillus thuringiensis Strains from Syria and their Toxicity to the Mediterranean Flour Moth Ephestia kuehniella Zeller (Pyralidae: Lepidoptera)

Bacillus thuringiensis was found in all tested different ecosystems in Syria. It was highly abundant in soils. A total of 219 isolates (97%) of B. thuringiensis producing parasporal crystals was classified into eight biochemical types. Bacillus thuringiensis subsp. kurstaki was the most common. Out of 219 strains, 192 strains (88%) were toxic to the third instar larvae of Ephestia kuehniella Zeller (Pyralidae: Lepidoptera). The highest toxic strains were isolated from cultivated areas and characterized by producing both bipyramidal and cuboidal parasporal crystals. Relationship between crystal shape and toxic activity was observed. The frequency of toxicity was greater in strains that produced bipyramidal parasporal crystals than strains that produced spherical crystals. Polymerase chain reaction (PCR) analysis of bacterial isolates gave characteristic products that allowed rapid prediction of the insecticidal activity. Insecticidal activity predicted by the PCR screen was found to correspond with the insecticidal activity of insect bioassay. The most toxic strain harbored different specific cry genes including cryI and cryIV genes which are insecticidal for Lepidopteran and Dipteran insects.