First National-Scale Evaluation of Temephos Resistance in Aedes Aegypti in Peru.

Background: Resistance of Aedes aegypti to insecticides can lead to operational failures in control programs. Knowledge of the spatial and temporal trends of this resistance is needed for effective monitoring, on which vector control decision-making should be based. Methods: : The organophosphate insecticide temephos was evaluated in L3 larvae in dose-response bioassays with eleven concentrations of the insecticide, following WHO recommendations. The mosquitoes tested were Ae. aegypti larvae of F1 and F2 generations from eggs collected with ovitraps during 2018 and 2019. Results: : The results segregated into two geographic groups. The first group, from the coast, was mostly resistant to temephos (RR > 10), with three populations (AG, CR and LO) showing RR values greater than 20 (AG 21.5, CR 23.1, LO 39.4). The populations in the second group, from the jungle of the Amazon and high jungle, showed moderate levels of resistance (defined as RR values between 5 and 10) with values ranging between 5.1 in JN and 7.1 in PU. Exception in this region was the population of PM, which showed a RR value of 28.8 to this insecticide. Conclusions: : The results demonstrate that Ae. aegypti populations in Peru present different resistance intensities to temephos, even after the suspension of its widespread use. Resistance to this larvicide should continue to be monitored because it is possible that resistance to temephos could decrease in the absence of routine selection pressures.