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In the present study, in order to control mosquito vectors in the field, a new aqueous formulation was developed using an indigenously isolated bacterial strain of Bacillus thuringiensis israelensis VCRC B646. The composition of formulation was, Bti lyophilized powder (5%), sodium benzoate (0.15%), sodium alginate (2.5%), Congo red (0.03%), citric acid (0.15%), glycerol (6%), molasses (8%) and polyethylene glycol (3%) in 100ml of water. Laboratory bioassay was carried out using this formulation against the late third instar of mosquito larvae. The result showed that the LC50 and LC90 values against Aedes aegypti, Culex quinquefasciatus, and Anopheles stephensi were 0.0082 and 0.016 mg/ l, 0.0084 and 0.0172 mg/ l, 0.0139 and 0.0294 mg/ l, respectively. Results from simulated field trial showed that the efficacy of Bti formulation at LC90 level was highly significant up to six weeks (42 days). Thereafter, the formulation efficacy was started declining. No side effect was observed against non-target aquatic organisms. It was concluded from this study that the formulation developed from newly isolated strain if B. thuringiensis israelensis VCRC B646 was very useful on the control of mosquito vectors.
Vijayakumar et al. (Thu,) studied this question.