Evaluation of resistance to pyrethroid and organophosphate adulticides, and kdr genotyping in Ades aegypti populations from Roraima, the Northernmost Brazilian State

Abstract

Background Roraima is the northernmost State in Brazil and makes international borders with Venezuela and Guyana. Although mostly covered by the tropical forests, the urban centers are highly infested with Ae. aegypti and endemic for dengue, Zika and chikungunya. Here we presented the levels of Ae. aegypti infestation and number of arboviruses cases between 2015 and 2018 in the studied localities. We evaluated the insecticide resistance status of Ae. aegypti populations from the capital Boa Vista, two cities in international borders: Pacaraima and Bonfim, and Rorainópolis in the limit with Amazonas State, collected in 2016 and 2018. Methods WHO like tube tests with the pyrethroid deltamethrin (0.05 and 0.12%) and the organophosphate malathion (0.7%) were conducted. Genotyping of kdr mutations, related to resistance to pyrethroids, were performed for the SNP variations in the sites 1016 and 1534 of the voltage gated sodium channel gene (Na V ) with a TaqMan qPCR approach. Results Only Ae. aegypti was present in our collection, meaning that there is still a barrier that Ae. albopictus was still not able to transpose from Amazonas toward Roraima. All Ae. aegypti populations were susceptible to 0.7% malathion in 2016, however mortality dropped to under 90% in Bonfim and Pacaraima in 2018. All populations were resistant to 0.5% deltamethrin in both years. The time that 50% of females suffered knockdown ( Kd T 50 ) under exposition to 0.5% deltamethrin was 3.3-5.9 fold longer in mosquitoes from the populations compared to Rockefeller. Only Pacaraima (2018) remained resistant to 0.12% deltamethrin. The kdr genotyping revealed the absence of the wild-type Na V S haplotype (1016Val + 1534Phe) in populations from Roraima, meaning that all tested individuals had a genetic background for resistance to pyrethroid. The double kdr Na V R2 haplotype (1016Ile + 15434Cys) was under higher frequencies in all populations except Rorainópolis, where this haplotype seems to have arrived recently. Conclusions These results are important to the knowledge about insecticide resistance status of Ae. aegypti populations from Roraima and will help to improve vector control strategies that may be applied to diverse localities with similar conditions.