New Strains of Bacillus thuringiensis subsp. israelensis Highly Toxic for Aedes aegypti and Culex pipiens pipiens

Bacillus thuringiensis subsp. israelensis (Bti) is the most extensively researched and well-documented subspecies of crystal-forming entomopathogenic bacteria employed for the control of blood-feeding mosquitoes. In this study, three Bti isolates (4369, 4929, and 4999) were extracted from intestines of a natural population of larvae of the blood-sucking mosquito Aedes flavescens. The bacterial isolates were identified by sequencing of the 16S ribosomal RNA gene and serotyping, which revealed that they belong to Bti serotype H14. The strains exhibited variations of their bacterial colony morphology, a range of distinctive biochemical characteristics, and distinct protein endotoxin profiles. The new strains Bti 4369 and 4999 demonstrated pronounced insecticidal efficacy. Half-maximal lethal concentrations toward Culex pipiens pipiens and Aedes aegypti larvae ranged from 1.39 × 10–4 to 2.26 × 10−4 μg/mL at 24 h post-treatment. Half-maximal lethal concentration of the Bti 4929 strain was found to be in the range of 32.7 × 10−4 to 35.9 × 10−4 μg/mL. The new strains of Bti have considerable potential for the development of biological agents for the control of blood-sucking mosquitoes.