Susceptiblity Detection And Resistance Mechanism Of Aedes Albopictus(Diptera:Culicidae) To Pyrethroid Insecticides In China

Aedes albopictus Skuse,1894,belonging to group of the Subgenus Stegomyia,Genus Aedes,was first found in Southeast Asia and is widely distributed in tropical,subtropical and temperate regions worldwide.Aedes albopictus is also widely distributed in China,and is the primary vector of Dengue fever,Yellow fever,Chikungunya fever and Zika,which have caused serious public health problems.Pyrethriods are the most widely and commonly used insecticides in China since 1980s because of their effectiveness and low toxicity,which have induced the resistance of Ae.albopictus throughout the country,therefore,challenging the prevention and control of insect-borne diseases.The strategies of this project were as follows:Firstly,diagnostic doses of Ae.albopictus to four pyrethriods were established,Field populations collected from Jinan Shandong,Baoshan Shanghai,Yangpu Shanghai,Hangzhou Zhejiang and Haikou Hainan were evaluated for the susceptibility statuses to the four pyrethroids using the diagnostic doses established.Then,metabolic detoxification and kdr alleles were detected and relationship between metabolic detoxification and kdr alleles to pyrethriod resistance were analyzed.In addition,bioassay effects of pyrethriod insecticide commodities to Ae.albopictus populations from Haikou were monitored consecutive two years.The results were as follows:1.The LC₅₀ values of deltamethrin,permethrin,beta-cypermethrin and lambda-cyhalothrin were 0.0062%,0.0501%,0.0064%and 0.0140%,respectively,while the LC₉₉ values were 0.0518%,0.5317%,0.1200%and 0.1186%,respectively.Thus the corresponding diagnostic doses to the four pyrethroids of Ae.albopictus in China were0.1036%,1.0634%,0.2400%and 0.2372%,respectively.2.Aedes albopictus populations from Jinan,Hangzhou,Baoshan,Yangpu and Haikou were all resistant to deltamethrin,permethrin,beta-cypermethrin,lambda-cyhalothrin as the mortality ranging 6.98%-76.60%,40.82%-85.23%,27.84%-71.58%and 38.30%-64.77%using the WHO tube assay with the diagnostic doses established.Aedes albopictus populations from Haikou has the highest resistance to the four pyrethriods,and pululations from Baoshan and Yangpu have the lowest resistance.3.Activities of GST and MFO of Ae.albopictus laboratory strain and field populations were measured,and base lines were established.Then,activities of GST and MFO of Ae.albopictus which had been exposed to deltamethrin and permethrin and were divided into resistant and susceptible groups according to their living conditions were detected and compared.However,there were no regular relationships between metabolic detoxification and pyrethriod resistance,which indicated that GST and MFO may have different effects among different resistant populations.In addition,R/S ratios of GST and MFO in resistant and susceptible groups exposed to permethrin were both greater than 1.It indicated that GST and MFO were closely related with the resistance of Ae.albopictus to permethrin,although the R/S ratio is not statistically significant4.Kdr alleles of I1532 and F1534 were found in 629 individuals of Ae.albopictus from five field populations,and simultaneous mutation of codon 1532 and 1534 in 24individuals were found in Baoshan and Yangpu population.Two alleles at codon 1532were wildtype ATC/I and mutant allele ACC/T,with frequencies 94.67%and 5.33%,respectively,and three genotypes were I/I,I/T and T/T,with frequencies 89.82%,9.54%and 0.64%,respectively.Four alleles at codon 1534 were wildtype TTC/F and mutant alleles TCC/S,TTA/L,and TGC/C,with frequencies 53.10%,44.20%,1.83%and 0.87%,respectively,and seven genotypes were F/F,F/S,F/L,F/C,S/S,L/L and S/C,with frequencies 37.52%,28.30%,2.38%,0.48%,29.41%,0.64%and 1.27%,respectively.This study first reported the novel mutant allele I1532T,and found a mutant allele TTA/L at the codon 1534 of Ae.albopictus in China.The relationship between kdr mutations and resistance phenotypes were analyzed and it indicated that I1532T had negative relationship with the resistance of Ae.albopictus to deltamethrin and F1534S had positive relationship with the resistance of Ae.albopictus to pyrethroids.5.It was found that the resistance of Ae.albopictus to pyrethroids was not caused by a single mechanism but by a variety of mechanisms after comprehensive analysis of this project.For different insecticides,metabolic detoxification was more important than kdr alleles for resistance to permethrin in Ae.albopictus,and metabolic detoxification and kdr alleles combined for resistance to deltamethrin in Ae.albopictus.For different populations,the level of resistance and the development process is different,but the contributions between metabolic detoxification and kdr alleles in different populaitons were not only different,but both complementary,jointly cope with insecitides.6.Bioassay effects of pyrethriod insecticide commodities to Ae.albopictus populations from Haikou were detected in 2016 and 2017 by the flask residualfilm method.The result showed that Ae.albopictus of Haikou had a widespread resistance to pyrethroids,leading to insignificant effects of pyrethroids with single component,especially for deltamethrin.But the effect of insecticides with mixture components was remarkable.In this study,the establishment of diagnostic doses of Ae.albopictus to four pyrethriods could provide the basic data for monitoring the resistance of field populations;the detectation of the susceptibility status of five Ae.albopictus populaitons to the pyrethroids had supplemented and improved the monitoring data of resistance of Ae.albopictus in China;the study on mechanism of resistance could provide theoretical basis for the developments of new molecular markers for monitoring resistance and effective mosquito control strategies.