Abstract
Bacillus sphaericus Neide (B) and B. thuringiensis serovar israelensis (Bti) de Barjac provides effective alternatives to broad spectrum larvicides in many situations, with little or no environmental impact. Taking into account environmental benefits including safety for humans and other non-target organisms, reduction of pesticide residues in the aquatic environment, increased activity of most other natural enemies and increased biodiversity in aquatic ecosystems, their advantages are numerous. In addition to recombinant bacteria used as larvicides, research is also underway to develop transgenic algae and cyanobacteria using larvicidal endotoxins of Bti and Bs. The advent of recombinant DNA technology is now having an enormous impact on agriculture and medicine, and it is appropriate that the ability to manipulate and recombine genes with this technology be applied to improving larvicides for vector control. These new recombinant bacteria are as potent as many synthetic chemical insecticides, yet are much less prone to resistance, as they typically contain a mixture of endotoxins with different modes of action. The existing recombinants also have what can be considered disadvantageous, in that they do not show significantly improved activity against aedine and anopheline mosquitoes, in comparison to Bti. But it may be possible to overcome this limitation using some of the newly discovered mosquitocidal proteins, such as the Mtx proteins and peptides such as the trypsin-modulating oostatic factor, which could be easily engineered for high expression in recombinant bacteria. While other microbial technologies such as recombinant algae and other bacteria are being evaluated, it has yet to be shown that these are as efficacious and environment friendly as Bti and Bs. By combining the genes from a variety of organisms, it should ultimately be possible to design ‘smart’ bacteria that will seek out and kill larvae of specific vector mosquitoes. Thus, recombinant bacteria show excellent promise for development and use in operational vector control programs, hopefully within the next few years.
Highlights
Mosquitoes are a source of great nuisance to human beings and pose a threat to public health, as vectors of diseases like malaria, filariasis, dengue, Japanese encephalitis, West Nile fever [1,2]
In addition to recombinant bacteria used as larvicides, research is underway to develop transgenic algae and cyanobacteria using larvicidal endotoxins of Bacillus sphaericus (Bs). thuringiensis serovar israelensis (Bti) and Bs
The advent of recombinant DNA technology is having an enormous impact on agriculture and medicine, and it is appropriate that the ability to manipulate and recombine genes with this technology be applied to improving larvicides for vector control
Summary
Mosquitoes are a source of great nuisance to human beings and pose a threat to public health, as vectors of diseases like malaria, filariasis, dengue, Japanese encephalitis, West Nile fever [1,2]. The 2362 strain of Bacillus sphaericus, which produces a binary toxin highly active against Culex mosquitoes, has been developed recently as a commercial larvicide It is being used currently in operational mosquito control programs in several countries, including Brazil, France, India, and the United States. A potential key strategy for delaying resistance to insecticidal proteins is to use mixtures of toxins that act at different targets within the insect, especially mixtures that interact synergistically This hypothesis was tested for delaying the phenotypic expression of resistance, by exposing Culex quinquefasciatus say larvae to Bs alone or in combination with Cyt1A, from Bacillus thuringiensis subspecies P. israelensis. Far studies have most commonly shown the resistance mechanism to involve a change in the membrane receptors, to which activated Bti toxins bind [71]
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