Bioassay of some important insecticides against the adults of two populations of Culex vishnui Theobald prevalent in Mandya and Mysore, Karnataka State (India)

Susceptibility of the adults of two populations of an important Japanese encephalitis (JE) vector, Culex vishnui Theobald, to diagnostic doses of permethrin (0.25%), deltamethrin (0.0227%), cyfluthrin (0.05), malathion (5.00%), DDT (4.00%) and propoxur (0.1%) was studied at different exposure durations. vishnui of Mandya was less susceptible to all these insecticides and showed respectively 1.03, 1.15. 1.24, 1.16, 1.02 and 1.39 times more tolerance than the Mysore population. On the basis of LT₅₀ values, malathion was the most effective at 5.0% concentration and DDT the least effective. All the three synthetic pyrethroids, viz, deltamethrin, permethrin and cyfluthrin were effective in very low concentrations. This has an added significance in view of the repeated outbreaks of JE in Mandya district with vast stretches of rice fields.