Abstract: The resistance levels to various insecticides, the distribution of the esterase genotypes, and the genetic diversity of five different field samples of Culex pipiens complex were studied by bioassay, protein electrophoresis, and the analysis of resistant alleles. Using the sensitive lines S-LAB as the control, the bioassay results indicated that the five Cx. populations showed higher resistance against dichlorovos, parathion, deltamethrin and permethrin, but lower resistance against propoxur, bassa, and tetramethrin. Chaoyang population had the highest resistance (55.7-fold) to dichlorovos, followed by Wuhan population. Foshan population also had higher resistance levels with 123-fold to permethrin and 23.9-fold to deltamethrin. The esterase electrophoresis indicated that the five Cx. populations showed different phenotype polymorphisms. The esterase of the Cx. populations from Guangzhou and Foshan exhibited the highest phenotype polymorphism with B1, A2-B2, A8-B8, A9-B9, B10 and A11-B11, suggesting that the over-produced esterases be the main mechanisms for resistance. Population genetics results indicated that the number of average allele, average polymorphism site, average expected heterozygosity, differentiation coefficient (Fst) and average gene flow (Nm) were 2.76, 66.45%, 0.1943, 0.10 and 2.57, respectively. The results showed that the five Cx. populations have a wealth of genetic diversity and the genetic diversity within populations is higher than that between populations. It is so inferred that the genetic diversities and the resistance levels became more identical through gene communication among the field populations by migration or others. This study may provide a guide to integrated pest management for Cx. pipiens complex in China.

Key words: Culex pipiens complex, insecticide resistance, esterases, population structure, genetic diversity, isoenzyme