Abstract
Bacillus thuringiensis subsp. israelensis (Bti) is the first Bacillus thuringiensis to be found and used as an effective biological control agent against larvae of many mosquito and black fly species around the world. Its larvicidal activity resides in four major (of 134, 128, 72 and 27 kDa) and at least two minor (of 78 and 29 kDa) polypeptides encoded respectively by cry4Aa, cry4Ba, cry11Aa, cyt1Aa, cry10Aa and cyt2Ba, all mapped on the 128 kb plasmid known as pBtoxis. These six δ-endotoxins form a complex parasporal crystalline body with remarkably high, specific and different toxicities to Aedes, Culex and Anopheles larvae. Cry toxins are composed of three domains (perforating domain I and receptor binding II and III) and create cation-selective channels, whereas Cyts are composed of one domain that acts as well as a detergent-like membrane perforator. Despite the low toxicities of Cyt1Aa and Cyt2Ba alone against exposed larvae, they are highly synergistic with the Cry toxins and hence their combinations prevent emergence of resistance in the targets. The lack of significant levels of resistance in field mosquito populations treated for decades with Bti-bioinsecticide suggests that this bacterium will be an effective biocontrol agent for years to come.
Highlights
Mosquitoes are an enormous public health menace in transmitting various tropical diseases and generally as a nuisance [1]
The larvicidal activity of Bacillus thuringiensis subsp. israelensis (Bti) resides in at least four major crystal protoxins, of 134, 128, 72 and 27 kDa, encoded by cry4Aa, cry4Ba, cry11Aa and cyt1Aa respectively, all mapped on the 128 kb plasmid known as pBtoxis [53,54,55]
This implies a specific mode of action that is different to those of Bti Cry’s, but an insect-specific receptor may still be essential for the specificity of the Cyt toxins [133,140]
Summary
Mosquitoes are an enormous public health menace in transmitting various tropical diseases and generally as a nuisance [1]. Chemical insecticides used in vector control programs harm the environment with adverse impacts on man and nature Resistance to such insecticides among mosquito species that are vectors of malaria (Anopheles gambiae) and. West Nile virus (Culex pipiens) emerged over 25 years ago in Africa, America and Europe and it is frequently due to loss of sensitivity of the insect's acetylcholinesterase to organophosphates and carbamates [6]. Alternative technologies such as biological control offer alternatives to deal with these problems and limitations [7]
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