| Objectives:We aimed to continuously monitor the density of Aedes albopictus in Pingshan District,Shenzhen,to grasp the density and seasonal fluctuations of Aedes albopictus in Pingshan District,and to explore the relationship between the density of Aedes albopictus and meteorological factors.In addition,we also monitored the insecticide resistance status of Aedes albopictus larvae in different habitats(industrial area,central area,ecological area)in Pingshan District,and explored the metabolic resistance mechanism and target-site resistance mechanism of Aedes albopictus,so as to provide a scientific basis for the continuous control of Aedes albopictus and the prevention of the spread,outbreak and epidemic of dengue fever in Pingshan District.Methods: 1.Surveillance on the density of Aedes albopictus:Placing mosquito oviposition trap: From 2015 to 2018,we randomly selected at least one residential area,park and hospital respectively to place mosquito oviposition traps each month.Breteau index survey: From 2015 to 2018,we randomly selected at least one residential area and the external environment(hospitals,parks,construction sites)respectively to conduct a Breteau index survey.2.Relationship between the density of Aedes albopictus and meteorological factors:The meteorological factors(month mean temperature,monthly precipitation,and monthly average relative humidity)from January 2015 to December 2018 were collected at Meteorological Bureau of Shenzhen Municipality.Spearman correlation analysis and stepwise multiple regression analysis were used to explore the relationship between the density of Aedes albopictus and meteorological factors.3.The detection of insecticide resistance of Aedes albopictus:The larval immersion method was used to detect the insecticide resistance of Aedes albopictus larvae in different habitats(industrial area,central area and ecological area).The activity of non-specific esterase(NSE),multifunctional oxidase(MFO)and glutathione S-transferase(GST)of Aedes albopictus in each population was measured by a microplate reader.Piperonyl butoxide(PBO)was used to indirectly measure the cytochrome P450 enzyme(P450s)activity level of Aedes albopictus larvae and explore the mechanism of metabolic resistance.Each Aedes albopictus was ground in liquid nitrogen to extract the DNA,and then the knockdown resistance gene(kdr gene)fragment was amplified by PCR to detect mutations in the kdr gene of Aedes albopictus and explore the target resistance mechanisms.Results: 1.Results of surveillance on the density of Aedes albopictus:The average MOI of Pingshan District in four years from 2015 to 2018 was 5.71.Comparing the MOI of different habitats,we found that the park has the highest MOI and the hospital has the lowest MOI.The MOI of Pingshan District showed a single-peak distribution every year from 2015 to 2018,and the peak density was mainly concentrated in June to September.The average BI for the four years from 2015 to 2018 in Pingshan District was 3.72,the container index(CI)was 23.71,and the housing index(HI)was 2.94.Comparing the BI of the two habitats,we found that the BI of residential area was higher than that of the external environment each year.The BI of Pingshan District showed a single-peak distribution every year from 2015 to 2018,and the peak density was mainly concentrated in July to September.2.Relationship between the density of Aedes albopictus and meteorological factors:The MOI and BI of Aedes albopictus were both positively correlated with month mean temperature,monthly precipitation,and relative humidity(P <0.001).The stepwise multiple regression analysis showed that when MOI was the dependent variable,the month mean temperature and monthly precipitation entered the regression equation(R = 0.789,P=0.006).And when BI was the dependent variable,the monthly precipitation and month mean temperature entered the regression equation(R = 0.774,P=0.012).3.Results of insecticide resistance of Aedes albopictus:Aedes albopictus larvae from the industrial area had high resistance to deltamethrin,while Aedes albopictus larvae from the central area and the ecological area were moderate resistance to deltamethrin,with resistance index of 24.13,17.74,18.81,respectively.Aedes albopictus from industrial area and central area were moderate resistance to beta-cypermethrin,with resistance index of 19.40,16.50,respectively.Aedes albopictus from industrial area and central area were moderate resistance to temephos,with resistance index of 12.38,18.10,respectively.Aedes albopictus from industrial area and central area were low resistance to permethrin and propoxur.Aedes albopictus from the ecological area was low resistance to beta-cypermethrin,temephos and permethrin,with resistance index of 7.70,8.82 and 3.26,respectively.Aedes albopictus from the ecological area was sensitive to propoxur.The activity of NSE,MFO and GST of Aedes albopictus larvae from the industrial area were higher than that of the sensitive strain with 1.31,1.56 and 1.21 times,respectively(P<0.05).The activity of GST of Aedes albopictus larvae from the central area and ecological area were higher than that of the sensitive strain with 1.43 and 1.19 times,respectively(P<0.05).The synergistic ratios of PBO to Aedes albopictus larvae in industrial,central,and ecological areas were 1.86,1.79,and 1.49,indicating that PBO enhanced the virulence of deltamethrin on Aedes albopictus populations in Pingshan District.The kdr gene of 108 Aedes albopictus were sequenced in Pingshan District.We found three alleles and five genotypes.In addition,the mutation rate of these 108 Aedes albopictus was 5.56% and we found mutation at the 1534 site of the kdr gene.F1534 L mutation was found in the kdr gene of Aedes albopictus in the industrial area,with a mutation rate of 4.65%.The mutations in F1534 L and F1534 S of kdr gene of Aedes albopictus in the central area were found,with a total mutation rate of 11.43%.No mutation was found in the kdr gene of Aedes albopictus in the ecological area.Conclusions:1.The density of Aedes albopictus was high in Pingshan District from 2015 to 2018,and there was a potential risk of dengue fever transmission during the peak density period.The density of Aedes albopictus had a positive correlation with month mean temperature,monthly precipitation,and monthly average relative humidity.The meteorological factors including month mean temperature and monthly precipitation had a significant impact on the density of Aedes albopictus.2.Aedes albopictus in industrial and central areas had higher resistance to insecticides than ecological areas.The resistance of Aedes albopictus in the industrial area may be related to the increased activity of the metabolic enzymes of NSE,MFO,GST and P450 s and the mutation in F1534 L of the kdr gene.The resistance of Aedes albopictus larvae in the central area may be related to the increased activities of GST and P450 s enzyme and the mutations in F1534 S and F1534 L of kdr genes.The resistance of Aedes albopictus larvae in the ecological area may be related to the increase of GST and P450 s enzyme activities.3.According to the insecticide resistance level of Aedes albopictus in Pingshan District,it is recommended to strengthen regular monitoring of the insecticide resistance level against Aedes albopictus and its related resistance mechanisms,and formulate a scientific and reasonable mosquito management plan. |
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