Optimization of bio-insecticide production by Tunisian Bacillus thuringiensis israelensis and its application in the field

Bacillus thuringiensis israelensis biological larvicides represent a good approach to support vector borne diseases control programs targeting earlier aquatic larval stages to limit their adult mosquito spreading. BUPM98, a Tunisian B. thuringiensis israelensis strain, is highly active against Aedes aegypti larvae. For the production of BUPM98 bioinsecticide, an agricultural by-product medium consisting of gruel and soybean meal has been optimized. Optimization of the medium composition was performed with statistical methodology based on experimental designs. Accordingly, the optimum toxin production was 2375.36 ± 48.52 mg/L at the following conditions: K2HPO4: 60 mM, pH: 7.6 and soybean meal: 32 g/L, which led to an improvement of 30% compared to the starting conditions. The impact of water quality on the effectiveness of BUPM98 delta-endotoxins against Culex pipiens larvae was investigated. Indeed, under field conditions, the direct application of BUPM98 fermentation product in stagnant water pools reduced the immature density of C. pipiens larvae by more than 95% after 48 h of treatment. Prolonged residual action was observed until 14 days. In conclusion, BUPM98, a local strain of B. thuringiensis israelensis, is very promising bioinsecticide for mosquito population management in Tunisia.