BACKGROUND The longstanding application of insecticides for vector control without
periodic monitoring of the population response to these chemicals can
directly drive the selection of resistant populations of vector mosquitoes.
Tocantins is the newest state of the Brazilian Federation. Despite a
historically high number of dengue cases, studies and monitoring data
concerning insecticide resistance in the state are lacking.OBJECTIVES To verify the resistance status of Aedes aegypti from 10
populations distributed throughout the state connected by rivers and
roads.METHODS Between 50 and 150 ovitraps were installed in house gardens within each
municipality. Collection points were established based on the importance of
the towns and on geographic aspects. Dose response bioassays were performed
in accordance with World Health Organization guidelines. Molecular assays
were conducted to detect kdr mutations, which are related
to pyrethroid resistance.FINDINGS Of the 3,200 ovitrap paddles analysed, 25.8% contained eggs, with a total of
55,687 eggs collected. With the exception of Caseara, all evaluated
populations were considered to be resistant to temephos. The data showed
different levels of resistance to deltamethrin among the samples. Caseara
and Guaraí showed the lowest RR95 values. On average, the
NaVR1 kdr allele was most frequent (40.3%),
followed by NaVS (38.1%), and NaVR2 (21.6%). Palmas,
the capital of the state, had the highest frequency of kdr
alleles (87.5%).MAIN CONCLUSIONS With the exception of Palmas, the towns with the highest indexes (ovitrap
positivity, number and density of eggs), as well with high levels of
resistance and kdr alleles were located along the BR-153
road, indicating that the flow of people and cargo can contribute to the
dispersion of the vector and potentially resistance. This study contributes
substantially to knowledge regarding the insecticide resistance profile of
Tocantins mosquito populations; the data generated via the study could
facilitate the judicious use of insecticides by vector control programs.
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