Characterization of Bacillus thuringiensis isolated from soils in the Jazan region of Saudi Arabia, and their efficacy against Spodoptera littoralis and Aedes aegypti larvae

Pest control in Saudi Arabia depends on applying chemical insecticides, which have many undesirable considerations and impacts on the environment. Therefore, the aim of this study was to isolate Bacillus thuringiensis from different rhizosphere soil samples in the Jazan region for the biological control of Spodoptera littoralis and Aedes aegypti larvae. The samples were collected from the rhizosphere of different plants located in eight agricultural areas in Jazan, Saudi Arabia. Out of 100 bacterial isolates, four bacterial isolates belonging to Bacillus species were selected namely JZ1, JZ2, JZ3, and JZ4, and identified using classical bacteriological and molecular identification using 16S rRNA. JZ1 and JZ2 isolates were identified as Bacillus thuringiensis. SDS-PAGE analysis and the detection of the Cry1 gene were used to describe the two isolates JZ1 and JZ2 in comparison to Bacillus thuringiensis reference strain Kurstaki HD1 (BTSK) were revealed that slightly different from each other due to the place of their isolation and namely Khlab JZ1 and Ayash JZ2. The EC₅₀ of JZ1 and JZ2 isolates, BTSK, and the commercial biopesticide DiPEL 6.4 DF against the second-instar larvae of Aedes aegypti were 207, 932, 400, and 500 ppm respectively, while EC₅₀ against first-instar larvae of Spodoptera littoralis were 193.93, 589.7, 265.108, and 342.9, ppm respectively. Isolate JZ1 recorded the highest mortality while JZ2 isolate gave the lowest mortality. It can be concluded that the local isolate of JZ1 and JZ2 can be developed for bio formulations to be used in Spodoptera littoralis and Aedes aegypti biological control programs.