Mutations and intron polymorphisms in voltage-gated sodium channel genes of different geographic populations of Culex pipiens pallens/Culex pipiens quinquefasciatus in China

Background Culex pipiens pallens and Culex pipiens quinquefasciatus are the dominant species of Culex mosquitoes in China and important disease vectors.Long-term use of insecticides can cause mutations in the voltage-gated sodium channel(vgsc)gene of mosquitoes,but little is known about the current status and evolutionary origins of vgsc gene in different geographic populations.Therefore,this study aimed to determine the current status of vgsc genes in Cx.p.pallens and Cx.p.quinquefasciatus in China and to investigate the evolutionary inheritance of neighboring downstream introns of the vgsc gene to determine the impact of insecticides on long-term evolution.Methods Sampling was conducted from July to September 2021 in representative habitats of 22 provincial-level administrative divisions in China.Genomic DNA was extracted from 1308 mosquitoes,the IIS6 fragment of the vgsc gene on the nerve cell membrane was amplified using polymerase chain reaction,and the sequence was used to evaluate allele frequency and knockdown resistance(kdr)frequency.MEGA 11 was used to construct neighborjoining(NJ)tree.PopART was used to build a TCS network.Results There were 6 alleles and 6 genotypes at the L1014 locus,which included the wild-type alleles TTA/L and CTA/L and the mutant alleles TTT/F,TTC/F,TCT/S and TCA/S.The geographic populations with a kdr frequency less than 20.00%were mainly concentrated in the regions north of 38°N,and the geographic populations with a kdr frequency greater than 80.00%were concentrated in the regions south of 30°N.kdr frequency increased with decreasing latitude.And within the same latitude,the frequency of kdr in large cities is relatively high.Mutations were correlated with the number of introns.The mutant allele TCA/S has only one intron,the mutant allele TTT/F has three introns,and the wild-type allele TTA/L has 17 introns.Conclusions Cx.p.pallens and Cx.p.quinquefasciatus have developed resistance to insecticides in most regions of China.The neighboring downstream introns of the vgsc gene gradually decreased to one intron with the mutation of the vgsc gene.Mutations may originate from multiple mutation events rather than from a single origin,and populations lacking mutations may be genetically isolated.

LETHAL AND SUBLETHAL EFFECTS OF ACETAMIPRID ON THE LARVAE OF CULEX PIPIENS PALLENS

Acetamiprid is a novel neonicotinoid insecticide invented by Nippon Soda Co., Ltd.. To explore the possibility of acetamiprid as larvicide of mosquitoes, lethal and sublethal effects of acetamiprid on the larvae of Culex pipiens pallens were studied by immersion method in the laboratory. The results indicated that the larvae of Culex pipiens pallens were sensitive to acetamiprid. The mortality of larvae peaked at 72 h after treatment. The 1st instar larvae was the most susceptible to acetamiprid, and the 4th instar larvae was the most tolerant to acetamiprid, the LC 50 values were 0.020 mg/L and 0.296 mg/L at 72 h after treatment, respectively. Sublethal concentrations of acetamiprid could delay the development of larvae and decrease the weight of pupa. We suggested that acetamiprid is a safe and effective substitute for the using larvicides of mosquitoes.

Experimental infections of mosquitoes with severe fever with thrombocytopenia syndrome virus

Background:Severe fever with thrombocytopenia syndrome(SFTS)is a newly identified emerging infectious disease,which is caused by a novel bunyavirus(termed SFTSV)in Asia.Although mosquitoes have not been identified as the primary vectors,as revealed by epidemiological surveys,their role in transmitting this SFTSV as a suspicious vector has not been validated.Findings:In this study,we conducted experimental infections of mosquitoes with SFTSV to examine the role of mosquitoes in the transmission of the virus.We did not detect viral replication in Culex pipiens pallens,Aedes aegyptis and Anopheles sinensis as revealed by qRT-PCR assay.In addition,we failed to isolate SFTSV from the Vero cells cultured with suspensions of SFTSV-infected mosquitoes.Conclusion:The results of the present study demonstrate little possibility that mosquitoes act as vectors for the emerging pathogen SFTSV.