Invasion of toxic marine cyanobacteria in to the tsunami affected coastal villages of southern India.

This documentation explores the facts about the invasion of marine cyanobacteria in to the tsunami affected coastal villages of Nagapattinam district of Tamilnadu and Karaikkal district of Pondicherry Union Territory (UT) in southern India. Water samples were collected from eight tsunami-hit coastal villages in different open water sources. The collected samples were processed for detecting marine cyanobacterial growth. Totally 110 water samples were processed, three samples were positive for the toxic cyanobacteria, Lyngbya sp., and nine for nontoxic species such as Epithemia sp.,, Johannesbaptistia pellucida, Oscillatoria princeps, Phormidium fragile, Synechocystis sp. Besides posing a public health risk because of the toxic cyanobacteria, the bloom formation by the cyanobacterial species such as Anabaena, Microcystis, Lyngbya, Plectonema, Phormidium contaminated the water bodies and deteriorated the water quality in the tsunami affected villages. The study revealed that another kind of public health risk from the invasion of toxic cyanobacteria to the costal ecosystem during the tsunami. It is necessary, in this context, that the surveillance mechanism, which is geared up during or after natural disasters, should have a provision to monitor the transportation of toxic elements/organisms from marine system to coastal/inland ecosystems and to control such organisms.

Tolerance of house fly, Musca domestica L. (Diptera: Muscidae) to dichlorvos (76% EC) an insecticide used for fly control in the tsunami-hit coastal villages of southern India.

The Directorate of Public Health (DPH), Tamil Nadu, in southern India employed spraying of dichlorvos (76% EC) for quick elimination of fly concentrations in the tsunami-hit coastal villages at the concentration of 304g (a.i.)/10,000m(2). However, nuisance of house flies remained high particularly in temporary shelters and centralized relief kitchens. Susceptibility of house fly, Musca domestica to dichlorvos was determined in the laboratory to provide information for an effective management of this pest. Various concentrations of dichlorvos (76% EC) viz., 0.1, 0.2, 0.4, 0.6 and 0.8microg (a.i.) per fly, were tested using topical application against F(1) progenies of house flies collected 12 months after insecticide applications from different habitats in the tsunami-hit coastal villages. Fly mortality was recorded at 24h post treatment. Parallel controls were maintained for comparison. Mortality of the house flies varied between 17.5% and 100% and increased with an increase in dosage of the insecticide. Mortality was >80% at 0.6 and 0.8microg (a.i.) per fly. The LD(50) of dichlorvos tested against flies collected from different villages varied from 0.218microg (a.i.) to 0.235microg (a.i.) per fly and the LD(90) varied from 0.574microg (a.i.) to 0.639microg (a.i.) per fly. House flies collected from a rural village, Thirukanur that had never been exposed for insecticide treatment in the past one decade, when tested, the mortality varied between 92.5% and 100% and increased with concentration of dichlorvos. Mortality was >90% from 0.2microg (a.i.) per fly and the LD(50) was 0.0399microg (a.i.)/fly, while the LD(90) was 0.1604microg (a.i.)/fly. The LD(90) values of the flies collected from the tsunami-hit villages were 3.5-3.9 times higher than that of the flies collected from Thirukanur. Fly abundance remained high in tsunami-hit villages with no marked reduction, suggesting that the flies had developed tolerance to dichlorvos. It is suggested that for an effective management of these resistant populations changing insecticides, application of unrelated insecticide, together with an appropriate environmental sanitation measure is necessary to keep the population under check.

Bioefficacy of mosquito mat, coil and dispenser formulations containing allethrin group of synthetic pyrethroids against mosquito vectors.

The bioefficacy of mats, coils and dispensers containing allethrin group of synthetic pyrethroids was studied against laboratory strains of Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi. Except esbiothrin in the mat formulation which was 100 and 178 times more effective against Cx. quinquefasciatus than against Ae. aegypti and An. stephensi with KT50 of 0.005, 0.5 and 0.89 min. respectively, all the three allethrins in mat or coil formulations were equally effective against the three vector mosquitoes. When compared to mat formulations of d-allethrin and bioallethrin, mat formulation of esbiothrin was 156 and 144 times more effective against Cx. quinquefasciatus. It was 162 times more effective against Cx. quinquefasciatus than in the coil formulation. Dispenser containing d-allethrin was the least effective against Cx. quinquefasciatus (KT50: 2.65 min.) and Ae. aegypti (KT50: 4.68 min.) but as effective as coil against An. stephensi. When mat and dispenser heated or coil burnt continuously for 10 hours the knockdown was consistently above 60% in all the three vector species but mortality was not consistently > 60% in Ae. aegypti. Repellent effect of the formulations ranged from 0.0 to 80.3%, 0 to 57.3% and 59.2 to 78.3% against Cx. quinquefasciatus Ae. aegypti and An. stephensi respectively. Repellency was more against An. stephensi than against the other two species. Mats and coils deterred > 50% of the mosquitoes from feeding on the chicken (range: 50 to 99.52%) but in case of dispenser the effect was only 14.72 to 65.01%. The use of these formulations as a control tools in reducing man-vector contact is discussed.