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.
ABSTRACT
Background & objectives: Japanese encephalitis (JE) is one of the most important arboviral diseases of human beings with outbreaks in many parts of Southeast Asia including India. We present the entomological findings of an outbreak occurred in northern part of West Bengal during 2011-2012 with special emphasis on the role of JE vectors in different seasons. Methods: Adult mosquito collections were made with the help of mouth aspirators, aided by flash lights during day time resting inside human and animal habitations as indoor, and resting outside field grasses, bushes, underneath of culverts and bridges as outdoor, and in and around the pig enclosures and cattle sheds during dusk period in JE affected villages from Cooch Behar, Dakshin Dinajpur, Darjeeling and Jalpaiguri districts in North West Bengal. In all study villages, a long handled with enamel bowl dipper was used to obtain immature stages of mosquitoes from various breeding habitats. Results: A total of 19 different types of mosquito breeding habitats were examined for vectors of JE. From these habitats, 23.7 per cent were positive for breeding during the study period. Overall, nine different species were recorded through emergence, but none was positive for JE virus when subjected for detection of virus. Adult mosquitoes of more than 50 per cent of the potential JE vector species obtained through dusk and the rest through indoor and outdoor collections in all seasons. Altogether, 27 different species were recorded. Most of these were JE vectors. Interpretation & conclusions: Our results showed that in addition to Cx. vishnui subgroup, detection of JE virus antigen in Cx. quinquefasciatus indicated the possible maintenance of JE virus in nature through poor vector mosquitoes throughout the year. Since, all potential vector species reported elsewhere in India were also found in this region and fluctuated in density in different seasons, a proper integrated vector control programme needs to be implemented to control JE transmission.
ABSTRACT
The present paper deals with the toxicity evaluation of pesticides acephate and chlorpyrifos by applying dominant lethal test (DLT) on mosquito Culex quinquefasciatus taken as an experimental model. For this, the adult male mosquitoes emerging from LC20 treated larval stock were allowed to crossmate with normal virgin females under controlled conditions of mosquito rearing laboratory along with the parallel controls, separately for each pesticide. The eggs obtained from such females were allowed to hatch after which they were examined under suitable magnification. The number of unhatched eggs was taken as the measure for calculating the dominant lethality caused by the pesticides and the data was analyzed statistically by applying Student's t-test. The statistical analysis of the results for acephate treated groups was 9.49±1.50 as against 3.92±0.41 in the control groups and chlorpyrifos treated groups gave the value 9.94±1.92 as against 4.26±0.35 in the control groups. The results indicated that these pesticides induced significant (p<0.05) dominant lethality.