Monitoring Of Resistance Of Malaria Vectors To Insecticides In Yunnan Province

Objective: In order to strengthen the prevention and control of the anopheline vectorsin our province, to understand the drug resistance condition of mosquito vectors underthe pesticide long-term selection pressures by monitoring of the insecticide resistance,it is advantageous to guiding the mosquitos extermination and providing scientificbasis for reasonable application of insecticides.Methods:(1) In malaria endemic areas, Simao, Cuiyun, Linxiang, Luxi, Yuanyang,Mengla, Menglian, Ninger were chosen as test points (a spot for each place), thefollowing when choosing the survey sites should be taken into consideration that thelocal different vector types in the local season distribution, the biological andecological characteristics.Full sucking blood mosquitos were captured from the scenesurvey points), after spawning, they were fed to F1generations in laboratory, theywere tested after three days of the pupa eclosion.If having difficulty with raisingmosquitos or convenient with the field work, full sucking blood mosquitos could becaptured the eve before the experiment and brought to the lab to be raised till the thenext day morning for the test.(2) According to the WHO adult mosquitoes filter papercontact method to do the test,3~5representative spots were chosen to test thepesticides, each experiment repeated for at least two times, meanwhile with a blankcontrol. Results were excluded from further analysis when the mortality in thecontrols exceeded20%.The experimental group mortality rate was corrected using theAbbott formula when the control mortality was between5%and20%. Duringexposure, the number and the rate of mosquitoes knocked down was subsequentlyrecorded after10,15,20,30,40,50and60min. After exposure, mosquitoes were kept under observation for24h, supplied with10%sugar solution and then thenumber of death and survival was recorded after this24h period and mortality wascalculated. According to the three resistance classes defined by WHO: susceptiblewhen mortality was98%and100%(S); Preliminary resistant when mortality wasbetween97.9%and80%(M); Resistant when the mortality was lower than80%(R).(3)The data was organized, and the SSPS11.0statistical software was used to calculate50%knockdown,90%knockdown, and also the95%confidence limit of KT50andKT90to different pesticides.Results:(1) For each monitoring sites, An. minimus was susceptible to the DDT andMalathion, the mortality of An. minimus for DDT, Malathion both were100%; Themortality for Cyfluthrin(resistance level M) were97.5%in Simao; The mortality forDeltamethrin(resistance level R) were lower than80%in Luxi; The rest of the sites ofAn. minimus were susceptible (mortality100%) for insecticides. Mosquitoes wereexposed for60mins in the tubes in a vertical position.Tests were done withinsecticides used DDT4%, Malathions5%, Cyfluthrin0.15%and Deltamethrin0.05%.The first knockdown time ranged from4to8mins for pyrethroids and from10to15mins for DDT. Malathion was5.7mins. The60minutes knockdown rate rangedfrom98.8%to100%for DDT and from80.31%to100%for pyrethroids. Theexposure time to get KT50ranged from17to24mins for DDT and from9to29minsfor pyrethroids. KT50was15.2mins for Malathion. KT90ranged from28to44minsfor DDT and from16to68mins for pyrethroids.KT90was27.8mins for Malathion.DDT KT50, KT90from high to low were sequentially Simao, Linxiang and Cuiyun;Pyrethroids KT50, KT90from high to low were sequentially Luxi,Linxiang, Simao,Cuiyun.(2) For each monitoring sites in Mengla, the mortality of An. sinensis forDDT(resistance level M) were81.5%;The mortality for Malathion(resistance levelM)were94.1%; The mortality for Deltamethrin(resistance level M)were88.9%;Themortality for Cyfluthrin(resistance level R) were78%.In Yuanyang, the mortality ofAn. sinensis for DDT(resistance level R)were66.7%;The mortality forDeltamethrin(resistance level R)were44.5%.In Ninger,the mortality of An. sinensisfor DDT(resistance level R)were46.9%; The mortality for Malathion(resistance level S) were99.03%;The mortality for Deltamethrin(resistance level R)were41.2%;Themortality for Cyfluthrin(resistance level R) were34.5%.In Menglian, the mortality ofAn. sinensis for DDT(resistance level R) were79.5%;The mortality forDeltamethrin(resistance level R) were24.6%.Tests were done with insecticides usedDDT4%, Malathions5%, Cyfluthrin0.15%and Deltamethrin0.05%.The firstknockdown time ranged from7to24mins for pyrethroids and from5to14mins forDDT. Malathion was ranged from3to12mins. The60minutes knockdown rateranged from28.4%to43.2%for DDT and from20.5%to98.1%for pyrethroids. Theexposure time to get KT50ranged from72to135mins for DDT and from18to116minutes for pyrethroids. KT50ranged from21to38mins for Malathion. KT90rangedfrom215till795mins for DDT and from53to501mins for pyrethroids. KT90rangedfrom111to138mins for Malathion. DDT KT50from high to low were sequentiallyYuanyang, Ninger, Menglian, Mengla;DDT KT90from high to low were sequentiallyNinger,Yuanyang, Menglian, Mengla. Malathion KT50from high to low weresequentially Mengla, Ninger;Malathion KT90from high to low were sequentiallyNinger, Mengla. pyrethroids KT50, KT90from high to low were sequentially Menglian,Yuanyang,Ninger,Mengla;pyrethroids KT90from high to low were sequentiallyNinger,Menglian, Yuanyang, Mengla.(3) In Linxiang, the mortality of An.jeyporiensis for DDT(resistance level S) were100%; The mortality fordeltamethrin(resistance level M) were97.4%. Tests were done with insecticidesapplied DDT4%and Deltamethrin0.05%.The first knockdown time was14mins forDDT and was9mins for pyrethroids.The60minutes knockdown rate was100%forDDT and pyrethroids.The exposure time to get KT50was30.1mins for DDT and was23.4mins for pyrethroids; DDT KT90was46.4mins; Pyrethroids KT90was36.2mins.Conclusion:(1)An. minimus showed preliminary resistance against pyrethroids inSimao. The resistance level of Anopheles minimus was R to Deltamethrin inLuxi.Anopheles minimus from the rest were susceptible to insecticides.An.jeyporiensisshowed preliminary resistance against pyrethroids in Linxiang.(2)In each monitoringsites, An.sinensis from Ninger were susceptible to Malathion. The rest showeddifferent levels of resistance to4commonly used chemistry pesticides.(3)Knockdown rate of mosquito to insecticide was higher than mortality.It indicated that part ofmosquitoes recovered after they were knocked down.Therefore the vectors had astrong knockdown ability. While part of knockdown rate of mosquito was lowerthan mortality, mosquitos did not return after knockdown.It showed that thepesticides toxicity were quite high.From the test results, it was known that DDT andMalathion had a strong knockdown ability and a good effect of killing mosquitoes. Inaddition pyrethroids had had a strong anti-knockdown ability and the use of it shouldbe reduced or stopped, proper measures should be adopted to overcome or delay theemergence and development of the resistance of the mosquitoes.