Mutation in the knockdown resistance gene and population genetic structure in Culex tritaeniorhynchus from Guizhou Province.

BACKGROUND

Culex tritaeniorhynchus is the main vector of Japanese encephalitis virus. However, there is a gap in current research on the knockdown resistance gene (kdr) and population genetic structure of Culex tritaeniorhynchus in Guizhou Province, China.

METHODS

We collected 365 Culex tritaeniorhynchus mosquitoes from ten geographic populations in Guizhou Province in 2023-2024 and analyzed the genetic diversity of the kdr gene with mutation at locus 1014 and the mitochondrial DNA-cytochrome c oxidase subunit I (mtDNA-COI) gene by polymerase chain reaction (PCR) amplification and sequencing. Haplotype diversity and nucleotide diversity were also analyzed, and a haplotype network diagram and phylogenetic tree were constructed.

RESULTS

Only the L1014F mutation (TTA → TTT) was detected at locus 1014 of the kdr gene in Culex tritaeniorhynchus in Guizhou Province. The frequency of resistant alleles ranged from 0% to 8.8%, with higher frequencies observed in Dejiang (8.8%), Libo (7.1%), and Sandu (3.3%). All samples from the Xingren population were susceptible (SS). mtDNA-COI genes showed high haplotype diversity (Hd = 0.989), low nucleotide diversity (π = 0.023), low genetic differentiation among populations (Fst = 0.001-0.140), and high gene flow (Nm > 1), suggesting that the population of Culex tritaeniorhynchus in Guizhou Province has high genetic diversity and frequent gene exchange. The haplotype network and phylogenetic tree indicated that possible cryptic or novel species existed in Guizhou Province in addition to the dominant populations.

CONCLUSIONS

Overall, Culex tritaeniorhynchus has not yet developed widespread resistance to pyrethroid insecticides in Guizhou Province, and the risk of spreading resistance genes needs to be continuously monitored owing to high population genetic diversity and frequent gene exchange.