In the study a new aqueous formulation with the new mosquitocidal isolate of Bacillus cereus VCRC 641 was developed, and the residual activity was assessed from simulated field trials conducted in the natural environment. From laboratory bioassays, it was observed that the efficacy of aqueous formulation of Bacillus cereus was on par with lyophilized cell mass, as such. The LC50 values of formulated B. cereus against Culex quinquefasciatus, Anopheles stephensi and Aedes aegypti were 0.002, 0.009 and 0.008 mg L-1 respectively. Correspondingly, the LC50 values of lyophilized cell mass of B. cereus against these three mosquito species were 0.0019, 0.005 and 0.004 mg L-1 respectively. Finally, simulated field trial was carried out using formulated B. cereus and the residual efficacy against all three mosquito larval species revealed 100 per cent larval mortality up to seven days and 69 to 78 per cent mortality were up to 15 days. Thereafter, the mortality was declining gradually up to 21 days. It is concluded that the formulation of B. cereus may be used for mosquito control program.
In this study, search for new mosquitocidal bacterium was attempted from the gut content of the fresh water fish Clarias batrachus (walking cat fish) which resulted in the isolation of a highly potential mosquitocidal bacterium. The isolate was identified as Bacillus cereus VCRC 641 by Bacillus species specific molecular markers ilvD, pur and pycA gene sequence analysis. Laboratory mosquito larval toxicity assay (bioassay) against mosquito larvae revealed that this new isolate was highly potent against Culex quinquefasciatus followed by Aedes aegypti and Anopheles stephensi. The lethal concentration values at LC50 for these three mosquito species were 0.001, 0.004 and 0.007mg/ L respectively. Therefore, in the present study, this is the first report that a highly potential mosquitocidal bacteria of B. cereus VCRC 641 was isolated from the gut content of Clarias batrachus and suggested that it can be used for mosquito vector control program.
Bacillus cereus VCRC 641 was found to be an alternate larvicidal bacterial agent which was newly isolated from fresh water fish, Clarias batrachus (walking cat fish). The protein responsible for mosquito toxic effect was separated and purified by Sephacryl S-200 column chromatography and NATIVE PAGE. It was observed that a unique protein with molecular weight of 70kDa was the responsible factor for mosquito killing effect. Further analysis of the protein by liquid chromatography-mass spectrometry (LC-MS) it was identified as “Uncharacterized Protein”. The length of the uncharacterized protein was around 158bp. The uncharacterized protein was expected to have a molecular mass of 70 kDa, 51 amino acids, confidence score of 78.45 and mass of 206772.57. Therefore, in the present study we report for the first time that uncharacterized protein (70kDa) was the responsible factor for the mosquito killing effect.
An indigenous, novel, cost-effective, non-electric lethal ovitrap was designed for the dengue vector. The bacteria Bacillus cereus VCRC 641 was grown in a cost-effective culture medium of chicken feather waste. The culture supernatant was used as ovitrap attraction of the dengue vector of Aedes aegypti (Linnaeus 1762). Twenty experiments with 80 ovitraps, three experiments with 15,000 ovitraps, and three experiments with 3,000 ovitraps in the laboratory, outdoor and households respectively conducted, to assess the efficacy, showed that the ovitrap with B. cereus culture supernatant (10%) significantly attracted the gravid A. aegypti to lay eggs in all experimental traps. More importantly, the first instar larvae from the eggs on the traps had the mortality immediately. The novelty of this trap is proved to exhibit a dual function for attracting gravid mosquitoes and killing the newly emerged larvae. This is the first report asserting the dual role of a cost-effective, non-electric ovitrap to control dengue vectors. The ovitrap contains only simple components of a plastic bowl, a cylinder, and a plastic plate. The total cost of these materials per trap was Rs15 only. The laboratory study showed that the experimental ovitrap attracted >10 times the control traps (experimental: 1465.90±251.48 and control: 140.00±23.95). This is the first report about the efficacy of an indigenously designed lethal ovitrap for attracting dengue vector.
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