Dengue virus and insecticide susceptibility status of Aedes aegypti mosquitoes from Belagola village, Mandya District, Karnataka state: during and post-epidemic investigations.

Aedes aegypti mosquitoes collected during and after dengue virus epidemic season were exposed to diagnostic dosages of insecticides. Mosquitoes collected during the epidemic showed resistance to DDT only, while mosquitoes collected after the control measures showed tolerance to malathion and low resistance to DDT. Since there was no indication of malathion resistance in the mosquitoes collected during the epidemic, the second batch was subjected to malathion selection pressure for 8 generations to find out the mechanism of resistance in this strain. There was 2-4 fold increase in resistance to malathion. Polyacrylamide electrophoresis showed increase in intensity of three esterase bands after selection. Quantitative enzyme assays showed an increase in esterase activity by 3-4 folds. Mosquitoes collected during the epidemic showed higher susceptibility to dengue-2 virus as compared to the laboratory strain, while the mosquitoes collected after malathion fogging showed further increase in the susceptibility to dengue virus. Virus susceptibility of the mosquitoes after eight generations of selection with malathion did not show any further significant increase.

Experimental studies on the vector potential of certain Culex species to West Nile virus.

Experimental studies were carried out to determine the vector potential of four species of mosquitoes to West Nile (WN) virus, viz. Culex tritaeniorhynchus, Cx. vishnui, Cx. bitaeniorhynchus and Cx. univittatus. All the four species of mosquitoes successfully transmitted and supported the growth of WN virus. The study indicated that the four species of mosquitoes could act as potential vectors of WN virus in nature.

Studies on the mosquito vectors of Japanese encephalitis virus in Mandya District, Karnataka, India.

Entomological investigations were carried out in areas affected by Japanese encephalitis (JE) in Mandya District, Karnataka, India, from 1983 to 1988, to determine species composition and the density of mosquito vectors, in relation to the incidence of JE cases. JE cases occurred in two spells in a year, one during April-June (summer epidemic) and another during October-December (winter epidemic). There was very high incidence of JE cases in extensively irrigated areas and a low incidence in some of the taluks with less or no irrigation systems. Among culicines, Culex tritaeniorhynchus was the most predominant species (20.54%), followed by Cx. fuscocephala (16.94), Cx. vishnui (16.48%), Cx. gelidus (10.70%) and other species. The overall mosquito population showed two peaks in a year, one during the March-April, and another during September, usually preceding the human epidemics. Relative abundance of certain species varied in different years.