ABSTRACT
Mosquitoes are the most deadly vector for transmitting several diseases, including malaria, filariasis, Japanese encephalitis, dengue, dengue hemorrhagic, and yellow fever. Nowadays, the particular stages of mosquitoes (larval, pupa, and adults) are controlled using synthetic chemicals. However, a major drawback with the use of chemical insecticides are that they are nonselective and can be harmful to other organisms in the environment, and are nonbiodegradable. To overcome these problems, there is an urgent need for searching novel insecticides from living organisms. Recently, entomopathogenic microbes are used to control mosquitoes as an alternative to chemical insecticides. In this study, entomopathogenic bacteria were isolated from agricultural soils of Salem, Tamil Nadu, India. Based on the morphological, physiological, biochemical, and molecular characters, the isolates were identified as Bacillus cereus. Phylogenetic analysis of the 16S rRNA gene sequence of B. cereus isolates show similarity among the closely related Bacillus strains. A toxicity assay was performed using B. cereus extracts against mosquito larvae and the results revealed the Aedes aegypti (a vector for dengue fever) is more susceptible than the other two species (Anopheles stephensi and Culex quinquefasciatus). The LC50 and LC90 values for third and fourth instar larvae of Ae. aegypti were 51.119, 52.694, and 56.513, 58.257 mg/L, respectively. No effect of B. cereus was found on nontargeted organisms. This study concludes that nonspore formers, especially bacteria, could arrest the growth of Ae. aegypti, An. stephensi, and Cx. quinquefasciatus larvae through producing secondary metabolites, which are nontoxic to the human population and the environment.
