Study On The Resistance Mechanism Of Aedes Albopictus To Volatile Pyrethroids

The Asian tiger mosquito（Aedes albopictus）,regarded as the most invasive mosquito species in the world,is the primary vector of dengue virus disease,which seriously threatens human health.Currently,the use of high-efficient and low-toxic volatile pyrethroids is one of the most important measures to control the population of Aedes albopictus.Widespread use of pyrethroids to contral Aedes albopictus has resulted in high selection pressure that has driven field-evolved resistance to pyrethroids.And furthermore,field mosquito resistant populations often exhibit complex resistance mechanisms as a consequence of the variety of insecticides used,such as reduced sensitivity of the target site,a lower insecticides penetration,its sequestration,and its biodegradation often called metabolic resistance.Alone or in combination these mechanisms confer resistance,sometimes at an extremely high level,to all of the available classes of insecticides.Monitoring insecticide resistance and characterizing molecular mechanisms underlying resistance is crucial to improve resistance management strategies and minimize disease transmission.In this paper,the repellency and knockdown activities and mechanism of resistance of field strain Aedes albopictus to four volatile pyrethroid including,dimefluthrin,metofluthrin,meperfluthrin and es-biothrin were studied in Dongfeng Town,Zhongshan City.The main study results were as follows:（1）Using Arm-in-cage assay,the repellent activities of the volatile pyrethroids dimefluthrin,metofluthrin,meperfluthrin and es-biothrin against Aedes albopictus were determined.The results showed that the repellency rate of metofluthrin,dimefluthrin,metofluthrin and es-biothrin to susceptible strains and field strains of Aedes albopictus were67.26%,48.67%,38.17%and 35.27%;56.15%,36.74%,34.95%and 29.61%,respectively.There was no significant difference in repellency between susceptible and field strains of meperfluthrin and es-biothrin.（2）The knockdown activity of dimefluthrin,metofluthrin,meperfluthrin and es-biothrin field strain Aedes albopictus was determined by Arm-in-cage assay and a closed-flask fumigation method.The results showed that the knockdown rate of metofluthrin was the fastest,the mortality rate of dimefluthrin is the highest.The KT₅₀ value of metofluthrin,dimefluthrin,and meperfluthrin to susceptible and field strain Aedes albopictus were 19.276min,21.605 min and 40.514 min;26.111 min,43.262 min and 78.411 min,respectively by Arm-in-cage assay.While the knockdown rate of es-biothrin less than 50%.The KT₅₀ value of metofluthrin,dimefluthrin,and meperfluthrin to susceptible and field strain Aedes albopictus were 7.509 min,11.358 min and 12.801min;9.245 min,13.582 min and 15.775min,respectively by the closed-flask fumigation method.The KT₅₀ value of es-biothrin susceptible Aedes albopictus was 34.584 min.While the knockdown rate of es-biothrin to field strain Aedes albopictus less than 50%.（3）The toxic activities of four volatile pyrethroids against field strain and field resistance strain Aedes albopictus were determined by larvae dip method and adult topical drop method.The results showed that the resistance rates of dimefluthrin,metofluthrin,meperfluthrin and es-biothrin to field strain and field resistance strain were 9.52,7.54,2.63and 6.77 times;42.55,33.92,6.58 and 8.02 times,respectively by larvae dip method.The results showed that the resistance rates of dimefluthrin,metofluthrin,meperfluthrin and es-biothrin to field resistance strain were 18.2,11.6,4.9 and 4.66 times respectively by adult topical drop method.The results showed that the cross-resistant rates of metofluthrin,meperfluthrin and es-biothrin to field resistant dimefluthrin strain were 4.99,2.98 and 1.18times.（4）The synergistic effect of the enzyme inhibitors PBO（piperonyl butoxide）and S2（octachlorodipropyl ether）to dimefluthrin,metofluthrin,meperfluthrin and es-biothrin were investigated by the method of treatment insecticide after the enzyme inhibitor and simultaneously treatment insecticide and the enzyme inhibitor.The results showed that PBO had the most significant synergistic effect on dimefluthrin,metofluthrin,meperfluthrin and es-biothrin,the synergistic ratios were 14.614,9.199,6.252 and 18.86 respectively by the method of treatment insecticide after the enzyme inhibitor;the synergistic ratios were 10.537,6.040,5.541 and 10.099 respectively by the method of simultaneously treatment insecticide and the enzyme inhibitor;and the synergistic effect of PBO on the pyrethroid by the method of treatment insecticide after the enzyme inhibitor was better than that of simultaneously treatment insecticide and the enzyme inhibitor.The synergistic effect of S2 on dimefluthrin,metofluthrin,meperfluthrin and es-biothrin were not obvious by the both methods.（5）The expression levels of field resistant strain Aedes albopictus of Cytochrome c oxidase subunit I,glutathione S-transferase,chymotrypsin,lipase 3,mitochondrial ribosomal large subunit,acetylcholinesterase,cytochrome P450 CYP6N3v1,L-lactate dehydrogenase and ATP synthase b subunit were significantly higher than that of susceptible Aedes albopictus and their expression levels were 79.8,11.5,13.5,7.5,9.6,6.8,6.7,4.9 and 3.3times than susceptible population respectively by quantitative real-time PCR.The expression level of field resistant strain Aedes albopictus of phosphorylase was 0.7 relative to susceptible Aedes albopictus.Further detecting showed that the expression levels of field resistant strain Aedes albopictus of three cytochrome c oxidase large subunits of I,II and III were significantly higher than that of susceptible Aedes albopictus and their expression levels were56.0,9.1 and 2.3 times than susceptible population respectively.（6）The domain II,III and IV of voltage gated sodium channel（VGSC）in field resistant strain Aedes albopictus were cloned and identified.The allele mutation（F1534S）occurred at F1534 site of voltage-gated sodium channel gene domain III.（7）The activities of the mitochondrial electron respiratory chain complexⅠ（NADH-coenzyme Q reductase）,Ⅱ（succinate dehydrogenase）,Ⅲ（cytochrome c reductase）,Ⅳ（cytochrome c oxidase）,MFOs,Na⁺/K⁺-ATPase and the content of ATP of field resistance strain Aedes albopictus were detected.The activity of the mitochondrial electron respiratory chain complexⅠ,Ⅱ,Ⅲ,Ⅳand V were 1.06,2.51,1.03,5.38 and 13.86 times relative to the susceptible strain Aedes albopictus;while the activity of MFOs and Na⁺/K⁺-ATPase was2.15 and 1.21 times relative to susceptive strain Aedes albopictus;The content of ATP was38.06%lower than that of the susceptive strain Aedes albopictus.（8）It was found that the metabolic rate of field resistant strain Aedes albopictus was1.67 times higher than that of susceptible strain Aedes albopictus by respirometry.