Impact Of Deltamethrin-resistance In Aedes Albopictus On Its Fitness Cost And Vector Competence

Background:Aedes albopictus,one of the most invasive species,has spread rapidly around the world in recent years.It is an important vector for mosquito-borne diseases such as dengue fever,zika virus disease and chikungunya fever.Chemical control of mosquitoes is an effective method to control mosquito-borne diseases,however,the wide and improper application of insecticides for vector control has led to serious resistance problems,making the prevention and control of mosquito-borne diseases a serious public health challenge.At present,there have been many reports on the resistance to pyrethroid insecticides in vector mosquitoes including deltamethrin to Aedes albopict us.However,the fitness cost and vector competence of deltamethrin resistant Aedes albopictus remain unknown.To understand the impact of insecticide resistant mosquito is of great significance for the prevention and control mosquitoes and mosquito-borne diseases.Objective:By establishing a laboratory resistant strain(Lab-R)of Aedes albopictus,the life table between the two strains as well as the vector competence for DENV-2 were comparatively analyzed.Methods:The Lab-R strain of Aedes albopictus was established by deltamethrin insecticide selecting from the laboratory susceptible strain(Lab-S).The deltamethrin resistance level of each generation of Lab-R strain was determined by larval impregnation method and insecticide susceptibility test of World Health Organization.Fitness cost of the 27th generation was analyzed and the evaluation indexes included pupation rate,eclosion rate,development time,survival time of adult mosquitoes,wing length,body weight and female fecundity.DENV-2 infection in mosquitoes was detected by RT-qPCR,The heads,salivary glands,midguts and ovaries of the two strains were dissected at 4,7,10 and 14 days post infection(dpi),and the infection rate and the amount of virus in each tissue were detected.On the basis of differences in vector susceptibility between the two strains during the later period of infection(14dpi),the horizontal transmission ability of the two strains was assessed by female mosquitoes biting 5-day-old healthy BALB/C suckling mice.The infection and virus titer in suckling mice were detected by RT-qPCR and plaque assay.During the later period of infection(14dpi),the ability of the two strains transmitting DENV-2 to their offspring was assessed by detecting eggs laid by females via RT-qPCR.Results:1.The laboratory strain of Aedes albopictus resistant to deltamethrin was successfully established;2.Compared with the Lab-S strain the larval development time of the Lab-R strain was prolonged,and the average survival time of adult mosquitoes was significantly shortened,especially the average survival time of female mosquitoes infected with DENV-2.There was no significant difference in wing length between female mosquitoes and between male mosquitoes of the two strains.The weight of resistant female mosquitoes was significantly higher than that of susceptible female mosquitoes,but no significant difference in weight between male mosquitoes of the two strains.In the second ovipostion cycle,all female mosquitoes fed with blood meal(without DENV-2)were allow to lay eggs in a single cup.The number of eggs laid by one resistant female mosquitoes was not statistically different from that of the susceptible female mosquitoes,regardless of whether the resistant female mosquitoes was infected with DENV-2.3.There were no significant differences in tissue infection rate and virus load between the Lab-R and Lab-S strains during the early period(4-10dpi)of DENV-2 infection,but in the later period(14dpi),the infection rate of tissues and the copy number of virus in positive tissues(except midgut tissues)of resistant female mosquitoes were significantly lower than those of the susceptible female mosquitoes.4.In the later period of DNEV-2 infection(14dpi),both stains of mosquito can transmit DENV-2 to mice,but the onset of viremia was later in the mice biting by resistant female mosquitoes,as well as lower virus copies in serum and brains.5.In the later period of DNEV-2 infection(14dpi),the infection rate of egg pools from the resistant strain was lower than that from the susceptible strain.Conclusion:Under the selecting pressure of insecticide,the deltamethrin resistant Aedes albopictus survived,but the deltamethrin resistance increased its fitness cost,prolonged the development time from larvae to adults,and shortened the average life span of adults.Meanwhile,in the later period of DNEV-2 infection,the resistance reduced the vector competence of Aedes albopictus.Considering the resistant still has the ability to transmit DENV-2,great attention should be paid to insecticide resistance in order to better guide the prevention and control of mosquito-borne diseases.