Adult population differences in response to six insecticides in Culex fuscocephala Theobald.

Adult bioassay was conducted in the laboratory on two populations of Culex fuscocephala, a vector of Japanese encephalitis (JE) in India, against two organochloride compounds (DDT and dieldrin), an organophosphate compound (malathion), a carbamate pesticide (propoxur) and two synthetic pyrethroids (deltamethrin and cyfluthrin) using WHO techniques. The adult populations from Mandya an irrigated agricultural area, and Mysore, a non-agricultural place in Karnataka, India, have been employed for the experiments. JE outbreaks were reported from these places at different times. Among the insecticides used malathion in 5% concentration was found to be the most effective while, cyfluthrin (0.05%) and deltamethrin (0.025%) were very effective in much lesser concentration. For both propoxur (0.1%) and DDT (4.0%) the two populations of Cx. fuscocephala expressed least susceptibility in terms of the LT50. Against dieldrin (0.4%), cyfluthrin, DDT and malathion Mysore population showed relatively more susceptibility than Mandya population. However for deltamethrin and propoxur the Mandya population registered less tolerance than the Mysore population. Thus adult population responses to different insecticides are variable in the present study.

Comparative susceptibility of two Japanese encephalitis vectors from Mysore to six insecticides.

Larval populations of Culex tritaeniorhynchus and C. fuscocephala from Mysore city were tested for their susceptibility against two pyrethroids viz., cypermethrin and deltamethrin and four organophosphorus (OP) compounds viz., fenthion, fenitrothion, temephos and malathion. The investigations revealed that, among the pesticides tested, efficacy of pyrethroids was very high as compared to OP compounds. C. tritaeniorhynchus was found to be highly tolerant to all the insecticides used. It registered 4.0, 6.5, 17.0, 6.5, 14.0 and 1.5 times more tolerance than C. fuscocephala to cypermethrin, deltamethrin, fenthion, fenitrothion, temephos and malathion respectively in terms of the LC50 value. Further studies are needed to determine the development of resistance if any, by C. tritaeniorhynchus, an important JE vector in Karnataka.