Evaluation and selection of the toxic activity of different strains of Bacillus thuringiensis and an extract of neem against Spodoptera exigua

People concern about the enviromental problems caused by the indiscriminated use of pesticides, made scientists think about more enviromental safe alternatives to reduce pest populations. The biological control arose as a viable alternative method with some promising results in the pest control. Biological control offer an enviroemntal friendly alternatives to chemical insecticides. About 2000 microorganisms are considered insect pathogens, including 100 bacetrias. Bacillus thuringiensis is an entomopathogenic baterium that has been applied as a bioinsecticide. Spodoptera exigua causes great economic losses to agricultureal crops. In this work we propose the use of the Bacillus thuringiensis and neem to control this insect pest. Moreover, we selected the Bacillus thuringiensis stains showing toxicity against Spodoptera exigua in order to find a strain of Bacillus thuringiensis with toxic activity against Spodoptera exigua. we probe toxic effect of HD1, HD2, HD9, HD29, HD73, HD125, HD133, HD227, HD551 and Bt154 of Bacillus thuringiensis. According to our results the strains HD133 and HD551 were selected as the most toxic strains that caused 66.06 and 63.89% mortality with dose of 50 µg of extract by mililiter of diet respectively. The toxicity of neem extract was 22.22 and 91.67 % with dose of 50 and 500 µg of extract, respectively. The neem extract caused hight mortality at high concentrations, but at low concentration the neem has a negative effect against the larvae in comparsion with the weight of the control larvae.