Pyrethroid resistance and distribution of kdr allele in Culex pipiens pallens in north China

A field survey was conducted to estimate resistance of Culex pipiens pallens, to pyrethroid insecticides in north China. We collected mosquito as egg rafts from 11 areas in Beijing and Zhangjiakou, Hebei province. Resistance to conventional pesticides, Es-bioallethrin, permethrin, deltamethrin, beta-cypermethrin, were measured using larval bioassays. The mutation kdr (L1014F) was also confirmed by sequence analysis. Our results indicate that the mosquitoes in north China still have a low or a moderate degree of resistance to pyrethroids. We then used competitive polymerase chain reaction (PCR) amplification of specific allele (cPASA) assay to monitor frequencies of kdr mutation in mosquito field populations. The kdr allele was present at frequencies of 7.9-37.8% in the field samples. Labeled allele-specific oligonucleotide hybridization (PCR-ASO) was performed and validated with cPASA. This proves that cPASA is an efficient molecular approach for monitoring insecticide resistance. Regression analysis indicated a significant correlation between kdr allele frequencies and the levels of resistance to knockdown resistance by permethrin, Es-bioallethrin, deltamethrin, and beta-cypermethrin. The results validate the role of the PCR-based molecular assay as a diagnostic tool in monitoring resistance to pyrethroids and also to provide useful information on population genetics of mosquito resistance to pyrethroids.