ABSTRACT
Aims: Aquatic habitat of the rice fields is the effective breeding site of the mosquitoes whose overcrowding would promote their pathogens. But no attention has been paid to these habitats for isolation and identification of the bacterial biocides. Therefore, the study was envisaged to isolate and identify the mosquitocidal bacteria from the unexplored rice field soil of the Burdwan district (a premier rice producer), West Bengal, India. It was also aimed to evaluate the virulence of the potent pathogenic organisms in the laboratory and field against the mosquitoes. Study Design: Laboratory and field study. Place and Duration of the Study: Parasitology and Microbiology Research Laboratory, Department of Zoology, The University of Burdwan, Burdwan 713104, West Bengal, India and Microbiology Laboratory, Crop Production Division, Central Rice Research Institute, Cuttack 753 006, Orissa, India. The study was conducted between June, 2011 to July 2012. Methodology: The soils were collected from the rice-fields, serially diluted up to 10-3 level, 100 μl suspension was plated on NA medium and incubated at 30±0.1ºC in the BOD incubator for 72 h. The colonies were checked under a phase-contrast microscope and those having spores were purified by dilution plating on NA plates. Phenotypic, biochemical and molecular characters of the bacteria were studied following standard methods. The mosquitocidal activity of the selected organism was assessed using different mosquito species both in the laboratory and field. Results: On the basis of phenotypic, biochemical and 16S rDNA (Acc. no. GU190368) analysis, the selected bacteria (Ts 116) was identified as Bacillus sp. In the laboratory, the LC50s of the Bacillus sp. Ts116 against late third instar larvae of An. subpictus, Ar. subalbatus and Cx. quinquefasciatus were (2.37, 2.2 and 9.6) X 106 bacteria/ml, respectively. After 7d, treatment with 100 ml suspension (containing 2.7x106 bacteria/ml) of bacteria/m3 breeding site effected 97.35, 95.65 and 100% mortality of An. subpictus, Ar. subalbatus and Cx. quinquefasciatus larvae, respectively. Conclusion: Indiscriminate use of chemical insecticides causes vector-resistance resulting in serious health and environmental hazards. The Bacillus sp. Ts116 (GU190368) of the rice fields had potential to be exploited in mosquito control programms.