Abstract
Objectives: Entomotoxic microorganisms are becoming very effective as biocontrol agents in alternative to chemical formulations. This study aimed to evaluate isolation, characterization, and determination of the larvicidal activity of Bacillus thuringiensis against Culex and Aedes larvae.
Methods: Bacteria were isolated from soil samples collected from major flour mills in Ilorin metropolis. The isolates were screened biochemically to obtain B. thuringiensis, which isolated were further subjected to molecular characterization. Larva toxicity was determined against Culex and Aedes larvae using standard procedure. Four densities of bacilli load were prepared using the McFarland turbidity standard 0.5, 1, 2, and 3, and the time range was 0-48 hours.
Results: Five isolates were obtained and named BT1, BT2, BT3, BT4, and BT5. All the isolates were toxic to the larvae tested. Bacillus thuringiensis isolated appears to be more toxic to Aedes larva than Culex larva. The most effective isolate was BT5, with a more than 65 % mortality percentage. The percentage occurrence of Bacillus thuringiensis among the isolates is 62.5%. Crystal (Cry) 1 and 2 protein gene occurs in 100 and 80 % of the isolates, respectively.
Conclusion: Formulations of B. thuringiensis from the isolates could serve as a form of biopesticide on mosquitoes and consequently control malaria and other mosquito-borne diseases of global health concern. J Microbiol Infect Dis 2021; 11(4):224-232.

Key words: Biopesticide, Larvae, Toxicity, Bacillus thuringiensis, Aedes, Culex