Characterization & larvicidal activity of indigenous isolates of Bacillus sphaericus from natural breeding habitats.

Soil, water and moribund/or dead mosquito larval samples collected from various mosquito breeding habitats of Pondicherry and Tamil Nadu were screened for the presence of mosquito pathogenic B. sphaericus isolates. From 1892 samples 21 isolates were obtained. All these isolates fell under 3 serogroups viz., H5a5b, H6 and H45, the latter two serotypes not reported hitherto as toxic to mosquito larvae and three phage-groups namely, phage group 2, phage group 3 and an unknown one. Twelve of the isolates were highly toxic and superior to the standard strains 1593, 2297 and 2362 supplied by Pasteur Institute, Paris when tested against Culex quinquefasciatus larvae. Out of these 12 strains 11 belonged to the serotype H5a5b and the phage-group 3 and 1 belonged to the serotype H45 and an unknown phage group.