Effectiveness of Bacillus thuringiensis and Bacillus sphaericus isolates against Culex pipiens, Aedes aegypti and Anopheles sergenti mosquito larvae

ABSTRACT

Mosquito borne diseases are continuing to be major health problems for exposed populations. Biological control alone or as a part of integrated vector management is believed to be a better alternative to the chemical control aimed against pest mosquitoes. The present study is designed to screen the larvicidal effect of Bacillus thuringiensis [Bf] and Bacillus sphaericus [Bs] against larvae of three species of mosquitoes larvae namely, Culex pipiens, Aedes aegypti and Anopheles sergenti. Mosquito Larvae were collected from different water resources and identified by standard procedures. Fourth-instar larvae were used in the bioassays. From the 50 samples of mud [15], soil [15] and water [20], 125 microbial isolates were purified and screened for larvicidal activity. The pure solubilized protein from Bs/Bt was quantified for protein estimation. For every 100 ml of the test solution 10 larvae were added in a 250 ml flask. Concentrations that killed 50% [LC[50]] and 90% [LC[90]] of the exposed mosquito larvae were determined. From a total of 125 bacterial isolates, only 25 isolates of Bt [13] and Bs [12] were found to have mosquito larvicidal effect. The highest larval mortality occurred with four isolates of Bt [Bt1, Bt2, Bt3, Bt4] and one Bs [Bs1] isolate. Their mortality rate [LC[50]] values were 0.0151, 0.0160, 0.0217, 0.0252 and 0.0330 mgI1, respectively. The [LC[90]] values of the five Bacillus isolates [Bt/Bs] were 0.0218,0.0219,0.0225,0.0341 and 0.0367, respectively. Time taken for larvicidal activity of the four Bt isolates showed LT[50] at 6,12,12 and 18 h and LT[100] at 24, 30, 36 and 48 h respectively. Bs showed LT[50] at 24 h and LT[100] at 48 h. This study confirms the utilization of larvicidal bacteria as Bt/Bs as commercial mosquito larvicidal and biological controlling agents