Temephos resistance and the associated cross-resistance spectrum in a strain of Culex quinquefasciatus Say (Diptera: Culicidae) from Peliyagoda, Sri Lanka

A heterogeneous population (Pel) of Culex quinquefasciatus Say was selected, by single family rearing, to give a strain, Pel SS, which had low levels of hydrolysis of the esterase substrates α and β-naphthyl acetate. The level of temephos resistance was three-fold lower in this strain than the original parental population, and the levels of resistance to malathion, fenitrothion, pirimiphos-methyl, chlorpyrifos and permethrin were also reduced. In contrast, temephos selection increased the temephos-resistance in the Pel-RR strain ten-fold compared to the original parental population and 29-fold compared to Pel SS. The level of temephos-resistance in Pel RR compared to Pel SS at the LC50 level was 37-fold. Larval cross-resistance, at different levels, was observed to the organophosphorus insecticides, malathion, fenitrothion, parathion, pirimiphos-methyl, chlorpyrifos, fenthion and phoxim, and to the carbamates, propoxur and bendiocarb, but the level of fenthion, propoxur and bendiocarb resistance was less than three-fold. Adults showed cross-resistance to malathion and fenitrothion, but not to propoxur. There was negative cross-resistance to permethrin in both the larvae and adults of Pel RR compared to the Pel and Pel SS strains.