Characterization and toxicity of Bacillus thuringiensis isolates from warehouses to Spodoptera exigua (Lep., Noctuidae)

Bacillus thuringiensis was isolated from 122 of 413 samples obtained from warehouses. Eighty-seven (71.31%) of these B. thuringiensis isolates were toxic to Spodoptera exigua, causing more than 60% mortality. Twenty-seven isolates were highly toxic to S. exigua, causing more than 95% mortality. Isolates 133, 47 and 58, which belonged to serotype H-7, H-4, H-4, respectively, were more active than the other isolates and their 50% lethality concentration (LC50) values were 17.93, 14.78 and 15.55 mug/ml, respectively. The isolate 133, 47 and 58 were analyzed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and polymerase chain reaction. The results showed that they contained similar to 135 and 65 kDa crystal proteins, that were similar with reference strain HD-1. Isolate 133 contained the cryIA(a), cryIA(b), cryIA(c), cryIE and cryII genes whereas both isolate 47 and 58 contained the cryIA(b), cryIA(c), cryIE and cryII genes; but they did not contain cryIII gene.