Microbial control of mosquitoes with special emphasis on bacterial control

There are a number of microbial agents including fungus, protozoa, virus and bacteria which act as mosquitocidal agents. However, among these agents, Bacillus thuringiensis var israelensis and B. sphaericus are the most potent mosquitocidal agents. Bacillus thuringiensis var israelensis and B. sphaericus are gram-positive sporulating bacteria which produce protoxin crystals during sporulation and are highly toxic to susceptible mosquito larvae when they ingest them. These bacterial agents are environmentally safe due to their host specificity, require in very low dosage, easy to prepare commercially in large-scale and are less costly. Field trials with various formulations of B. sphaericus and B. thuringiensis var israelensis have demonstrated their safety and potential for controlling mosquitoes. Moreover, cloning and expression of the toxin genes of these organisms in other environment friendly bacteria have also made them important for further investigation. Recent advances with novel types of recombinant micro-organisms with new cloning strategies and cloning the toxin genes under strong promoter for over expression together with in vitro gene manipulation and site directed mutagenesis of the active sites for increased toxicity have the potential to provide more effective control of mosquitoes by exploiting these two bacteria. But the toxins of B. sphaericus and B. thuringiensis var israelensis in particular, do not persist long in nature and require frequent application which is a limiting factor for these organisms to be most successful and potent biolarvicide. Nevertheless, they are by far the best choice for controlling mosquitoes. In this review article different mosquitocidal agents with particular emphasis on B. thuringiensis var israelensis and B. sphaericus have been described.