Heterogeneous duplication and point mutation of ace-1 confer organophosphates and carbamates resistance to Anopheles sinensis field populations in Guizhou Province, China.

backgroundGuizhou Province has historically been a region severely affected by malaria in China. For decades, vector control has served as a cornerstone of national efforts to control and eliminate malaria. However, the efficacy of this strategy is largely challenged by the development of insecticide resistance. In the present study, the resistance status to organophosphates (OPs) and carbamates (CBs) of Anopheles sinensis field populations across Guizhou Province was investigated with a primary focus on elucidating the underlying mechanisms.

methodsFrom 2017 to 2024, mosquitoes were collected intermittently using mosquito-killing lamps across Guizhou Province. An. sinensis specimens were identified using morphological and molecular methods. Subsequently, we genotyped the ace-1 gene via PCR and measured acetylcholinesterase1 (AChE1) residual activity using biochemical assays. Whole-genome sequencing of individual mosquitoes was performed using Illumina sequencing, and the copy number of the ace-1 gene was quantified by standard genomic DNA quantitative PCR. Two independent-sample t-test and a chi-squared test had been used in this study.

resultsFemale An. sinensis were collected from 12 field populations across Guizhou Province. Following species identification, point mutations in the ace-1 gene were detected in 551 mosquito samples. Only one point mutation, G119S, was identified across all populations, with the frequency of the ace-1 mutant genotypes (119GS and 119SS) exceeding 66% in 11 out of the 12 populations. Heterozygotes were the predominant genotype. The AChE1 activity was not inhibited by propoxur in 10 populations. A significant departure from Hardy-Weinberg equilibrium was observed in 6 of the 12 populations, indicating an excess of heterozygotes in these populations. Notably, heterogeneous duplication of the ace-1 gene in An. sinensis was detected for the first time through genomic scanning and ace-1 copy number quantification.

conclusionsResistance to OPs and CBs is widespread in An. sinensis populations across Guizhou Province. Both heterogeneous duplication and point mutation of the ace-1 gene in An. sinensis likely contribute to resistance to OPs and CBs. These findings highlight the necessity of monitoring duplicated resistance alleles in natural populations to formulate region-specific resistance management strategies.