Abstract: Chemical control is the main method to control mosquitoes that are the primary vectors of human diseases. Previous resistance investigations showed that mosquitoes in China had become resistant to organophosphates, organochlorines, carbamates and pyrethroids. There are two main resistance mechanisms, i.e., the target resistance and the metabolism resistance that three detoxification enzyme families are involved in. An insecticide-susceptible strain is indispensable for resistance monitoring and studies of resistance mechanisms. In this study, we established an insecticide-susceptible strain of Culex pipiens quinquefasciatus from a field population by screening the isofemale lines without the G119S mutation in the acetylcholinesterase and with the low activity of carboxylesterases, P450 monooxygenases, and glutathione-S-transferases. Compared to another susceptible strain, S-lab, the strain screened here had 1.5-old higher carboxylesterase activity and equivalent P450 and glutathione-S-transferase activities. Insecticide bioassay showed that this strain had a less than 2-fold resistance to organophosphates and no resistance to carbamates and pyrethroids compared to the S-lab. Therefore this strain can be applied as an insecticide-susceptible strain in resistance monitoring.

Key words:  Culex pipiens quinquefasciatus, insecticide-susceptible strain, acetylcholinesterase, carboxylesterase, P450 monooxygenase, glutathione-S-transferase, insecticide resistance