engineered bacillus thuringiensis var-israelensis (bti) for the biological control of mosquito-a review

Abstract

The number of pathogenic microorganisms that are capable of killing insectpests is extremely large. Some bacteria are more attractive to researchersdeveloping microbial biological control agents because their genomes aresimple enabling easier study and manipulation. Several bacterial speciesare already used on a large scale as control agents against some insects.Commercial preparation of these bacteria in theform of insecticidal powdersare available for use in the field. Although these preparations are somewhatmore expensive and also less e/jicient than chemical insecticides, for severalreasons including recent awareness of environmental safety, development ofbiological control agents has recieved increased attention of biologists.

Several varieties of Bacillus thuringiensis have been well studied fortheir to:xic effects on insects. These bacteria produce proteinaceous parasporalcrystals during their sporulation. When these crystals are ingestedby insect larvae protein protoxins are solubilised in the alkaline environment ofthe insect midgut releasing polypeptides toxic to the epithelial cells resultingin quick death of the larvae.

Toxicity of Bacillus thuringiensis var. israelensis is specific to mosquitoand blackfly larvae. However, large scale use of this bacterium for thecontrol of mosquitoes is limited by its low persistenee in the field afterapplication. Four genes coding for 4 different toxic polypeptides have beenisolated from this bacterium and all these have been cloned in E. coli andstudied. Research is being done to study the posible manipulation of thesegenes in order to obtain potentially much more efficient bacterial strains forthe control of insects.