Development of malathion resistance in Culex quinquefasciatus say (Diptera: Culicidae)

A malathion resistant colony of C. quinquefasciatus was developed in the laboratory. LC(50) and LC(50) for larvae were calculated at every generation and the values were 0.3 ppm and 1.13 ppm for first generation and 61.09 ppm, 136.3 ppm for 25th generation respectively. The fold increase in LC(50) and LC(50) were 2036 and 2726 folds respectively. Cross resistance against propoxur and chlorpyrifos showed 6.64 and 6.52 fold and 600 and 720 fold increase in their LC(50) and LC(50) values respectively. Triphenyl phosphate (TPP) and piperonyl butoxide (PB) were used as synergists and TPP indicated proportional decrease in LC(50) and LC(90) values while not much change was observed with PB. No change in biotic potential (larval hatchability, adult emergence and male and female ratio) between susceptible and malathion resistant colonies was observed.