| Background:Aedes albopictus is one of the most invasive species in the world.It is widely distributed worldwide and is an important vector for mosquito-borne diseases such as dengue fever,Zika virus disease,Chikungunya fever and yellow fever.At present,the removal of larval breeding sites and the use of insecticides are the main means of controlling Ae.albopictus.With the large use of insecticides,there is a possibility for insecticide resistance generation,especially the most commonly used pyrethroid insecticides.To determine insecticide resistance status and mechanisms in Ae.albopictus is very important for vector control.Aim:To explore the regularity and mechanism of resistance of Ae.albopictus to pyrethroid insecticides by the stablishment of laboratory deltamethrin-resistant strains.To investigate the resistant status and mechanism of Ae.albopictus to commonly used insecticides in the field populations of Guangzhou.To provid countermeasures and guidelines for the management of Ae.albopictus insecticide resistance in Guangzhou.Methods:In order to establish a deltamethrin resistant population,deltamethrin was used as a screening pressure in sensitive populations of Ae.albopictus.The deltamethrin resistance level of each generation was determined by larval impregnation method and WHO tubes test.During the screening process,the PCR and synergistic study was used to determine the role of kdr mutation and metabolic enzyme activity in the development of resistance.The fitness cost associated with resistant populations was analyzed by life table analysis and population fertility analysis.Ae.albopictus were collected from four districts with varied dengue occurence in Guangzhou from 2015 to 2017.Adult Ae.albopictus insecticide susceptibility status against commonly used insecticide were comparatively detected.Mutations at the voltage-gated sodium channel(VGSC)gene and acetylcholinesterase(AChE)gene were analyzed.The effect of cytochrome P450s on the resistance of Ae.albopictus to deltamethrin was tested using the synergistic agent piperonyl butoxide(PBO).A questionnaire survey of insecticide usage for public health regions was conducted in Guangzhou to provide assistance for pesticide management.Results:After 3 years of continuously selecting,a deltamethrin-resistant Ae.albopictus strain derived from laboratory sensitive strains was successfully established after 24 generations of selecting by the median lethal concentration(LC50)increased from 0.002mg/L to 0.033mg/L and adult mosquito mortality decreased from 100%to 81.2%.It is found that the growth of population resistance has experienced a process developed from zero and from slow to fast.With the development of population resistance,the proportion of allele F1534S(TTC-TCC)in the population increased gradually(from 0%to 47.06%in the population,and was significantly correlated with the increase of resistance.F1534S mutation can be used as a target site for possible deltamethrin resistance in Ae.albopictus for rapid molecular detection of resistance.Metabolic enzyme activity was not significantly associated with deltamethrin resistance when the population was at a lower level of resistance,but P450 monooxygenase(P450s)activity become significantly associated with resistance when population increased to 16.5 fold resistance fold.The development of population resistance is accompanied by the generation of fitness cost,which is mainly reflected in the decrease of population fertility.During the screening process,the population developed cross-resistance to insecticides such as permethrin and pyriproxyfen.In 2017,the field population of Ae.albopictus in Guangzhou is still sensitive to malathion,Bacillus thuringiensis subtypes(Bti)and hexaflumuron(the adult mortality>98%or LC50<5),but resistant to the other commonly used larvae and adult insecticides(the adult mortality<90%or LC50>5).From 2015 to 2017,the resistance of the Ae.albopictus population in Guangzhou to pyrethroid increased rapidly,and the average mortality against deltamethrin decreased from 95.3%to 31.2%,the average mortality against permethrin decreased from 98.6%to 55.8%.F1534S mutation(TTC-TCC)and F1534L mutation(TTC-CTC)were significantly associated with pyrethroid insecticides and dichlorodiphenyltrichloroethane(DDT)resistance,P450s activity were significantly associated with deltamethrin resistance too.Pyrethroids(mainly type I permethrin S-biomethrin,and type II beta-cypermethrin)were the most commonly used adulticides,while organophosphates(mainly temephos and fenthion)were the most commonly used larvicides.The frequency of insecticide usage in urban areas was more frequent than that in the rural district.The Ae.albopictus in Guangzhou has developed resistance to pyriproxyfen without pyriproxyfen used.Conclusion:The regularity and mechanism of resistance to deltamethrin in Ae.albopictus were elucidated for the first time:F1534S mutation was significantly associated with Ae.albopictus resistance and played a major role in the early stage of resistance development.And,F1534S mutation frequency increased simultaneously with the level of resistance.The F1534L mutation and P450s activity were also significantly associated with the production of deltamethrin resistance in Ae.albopictus,but it mainly works when the population is at a higher level of resistance.The resistance to deltamethrin in Ae.albopictus is accompanied with fitness cost by a decrease in population fertility.The field population of Ae.albopictus in Guangzhou has developed resistance to most commonly used insecticides,and the level of resistance has increased rapidly from 2015 to 2017.Cross-resistance between deltamethrin and pyriproxyfen was first found in Ae.albopictus.Based on the present study,we suggest to use malathion against adult mosquitoes and hexaflumuron or Bti against larvae for dengue vector control in Guangzhou. |
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