Natural insecticides from actinomycetes and other microbes for vector mosquito control

Abstract

Mosquitoes are the most dreadful bloodsucking insects in the world, and though tiny in size, they inflict most human deaths worldwide. They transmit deadly pathogens like Plasmodium, chikungunya virus, yellow fever virus, dengue virus, Japanese encephalitis virus and West Nile virus. Worldwide, there are 3500 species of mosquitoes grouped into 41 genera, but only 100 species are reported as vectors of human and other vertebrate diseases. India contributes nearly 34 % of global dengue and 11 % of global malaria cases. During the year 2012, nearly 1.13 million people were infected with dengue, malaria and chikungunya in India, and 766 succumbed to these diseases. In India, three genera, namely, Aedes, Anopheles and Culex, are the most common groups of mosquitoes found almost in all regions. Aedes spp. transmit dengue, chikungunya and yellow fever, Anopheles spp. transmit malaria, and Culex spp. transmit filariasis and Japanese encephalitis. In recent years, a decrease in the malaria and filariasis cases has been reported, but the number of infected cases and mortality due to dengue is steadily increasing. The failure in mosquito control is mainly due to the inefficiency of synthetic pesticides and repellents. Mosquitoes have developed resistance to almost all types of chemical insecticides. The increasing number of mosquito breeding sites and the destruction of mosquitoes' natural enemies are also contributing to the sudden rise in mosquito population and mosquito-borne diseases. Application of synthetic chemicals in water bodies is unsafe to humans and nontarget organisms. Microbial pesticides and botanical pesticides are eco-friendly and target specific compared to synthetic pesticides. Microbial pesticides obtained from actinomycetes, Bacillus thuringiensis (Bt), B. sphaericus (Bs) and many other microorganisms are reported as ecofriendly alternatives for mosquito control. A large number of Bt strains have been reported to possess insecticidal properties against different groups of insects. B. thuringiensis israelensis (Bti) is an important pathogenic bacterium to mosquitoes. The secondary metabolites of some microorganisms are potential toxins against mosquito larvae at very low concentrations. Spinosad, a potent insecticide, has been isolated from the actinomycete bacterium Saccharopolyspora spinosa. In this review, potentially effective actinomycetes and other microorganisms against mosquito larvae and their effective bioactive compounds are described. The review also presents up-to-date information on the efficacy of microbial pesticides in mosquito control, their biosafety, field efficacy and commercial applications.