Abstract
Insecticides derived from the common soil bacterium Bacillus thuringiensis are becoming increasingly important for pest management. Biological activities of the effective bacterial strains against the 2th and 4th instars larvae of the cotton leaf worm, Spodoptera littoralis (Boisd.) were isolated from tomato cultivated fields at Fayoum Governorate, Egypt. Out of 72 isolates, 12 with the most morphologically distinct-looking Bacillus colonies were selected and named A1, A2, A3, A6, A7, A9, A12, A13, A107, B37, B45 and B100. All isolates were preliminarily identified as members of the genus Bacillus based on morphological, physiological, and biochemical characteristics. When tested for their pathogenicity, against S. littoralis, the 12 isolates revealed varying efficacies, with isolates A1 and A9 being superior exhibiting maximum mortality of 90.0 and 83.33% on day 7, respectively. Isolate A7 recorded the lowest mortality percentage (20.0%). Further genetic characterization of the 12 isolates was performed using inter simple sequence repeat (ISSR), that randomly amplified polymorphic DNA (RAPD) and 16S rDNA gene sequencing analysis. RAPD and ISSR results confirmed each other. The combined ISSR and RAPD phylogenetic tree showed two major clusters. With 16S rRNA gene analysis, isolate A1 and A12 sequences recorded 100% identity with B. thuringiensis, while isolates A7 and B100 showed 95.7% and 95.6% identity with B. cereus and B. sphaericus, respectively. Additional work is in progress to optimize the cultural, nutritional, environmental and operational parameters needed for a successful large-scale production of the most effective isolated Bacillus strain (s).