BACKGROUND Knockdown resistance is conferred primarily by non‐synonymous mutations that reduce pyrethroids binding to voltage‐gated sodium channels. In 2014, kdr mutation V1016I in Aedes aegypti populations resistant to pyrethroids was reported for the first time in Colombiα, in 2016 another kdr mutation, F1534C, and in 2018 the mutation V419L. Nine populations of A. aegypti, previously characterized as being resistant to λ‐cyhalothrin, deltamethrin, cyfluthrin and permethrin, were used for this study. Genomic DNA was used to determine genotypes by allele‐specific PCR for mutations V1016I and F1534C, and to determine their association with pyrethroid resistance. RESULTS All the populations analyzed showed both mutations, with allelic frequencies of 0.07–0.35 for I1016 and 0.47–0.88 for C1534. A percentage of co‐occurrence of mutant homozygotes I1016/C1534 of 5.3% was detected. A significant positive correlation was found between the frequency of the genotype I1016 and the resistance to permethrin, λ‐cyhalothrin and cyfluthrin, but not to deltamethrin; on the other hand, the correlation was not significant for the C1534 genotype and the four pyrethroids evaluated. No significant correlation was found between the frequencies of the mutations V1016I and F1534C. CONCLUSIONS Both mutations V1016I and F1534C are present in A. aegypti populations of the Colombian Caribbean, and although the frequency of F1534C exceeds V1016I, the latter was correlated to resistance to pyrethroid insecticides. © 2018 Society of Chemical Industry

Aedes aegypti is the main vector of dengue, chikungunya, and Zika viruses, which are of great public health importance in Colombia. Aedes control strategies in Colombia rely heavily on the use of organophosphate and pyrethroid insecticides, providing constant selection pressure and the emergence of resistant populations. In recent years, insecticide use has increased due to the increased incidence of dengue and recent introductions of chikungunya and Zika. In the present study, pyrethroid resistance was studied across six populations of Ae. aegypti from the Caribbean coast of Colombia. Susceptibility to λ-cyhalothrin, deltamethrin, and permethrin was assessed, and resistance intensity was determined. Activity levels of enzymes associated with resistance were measured, and the frequencies of three kdr alleles (V1016I, F1534C, V410L) were calculated. Results showed variations in pyrethroid susceptibility across Ae. aegypti populations and altered enzyme activity levels were detected. The kdr alleles were detected in all populations, with high variations in frequencies: V1016I (frequency ranging from 0.15-0.70), F1534C (range 0.94-1.00), and V410L (range 0.05-0.72). In assays of phenotyped individuals, associations were observed between the presence of V1016I, F1534C, and V410L alleles and resistance to the evaluated pyrethroids, as well as between the VI 1016 /CC 1534 /VL 410 tri-locus genotype and λ-cyhalothrin and permethrin resistance. The results of the present study contribute to the knowledge of the mechanisms underlying the resistance to key pyrethroids used to control Ae. aegypti along the Caribbean coast of Colombia.

The use of insecticides for the control of Aedes aegypti (L.) (Diptera: Culicidae) in Colombia has indirectly influenced the susceptibility status of Culex quinquefasciatus Say populations. We evaluated pyrethroid susceptibility in two populations of Cx. quinquefasciatus in the Atlantico Department of Colombia and its possible resistance mechanism (kdr mutation). Bottle bioassays were performed for permethrin, deltamethrin, and λ-cyhalothrin in female mosquitoes of Cx. quinquefasciatus. The resistance ratios (RRs) for KC50 and LC50 for each insecticide in the field populations examined were determined, using the Cartagena strain as the susceptible control. The L1014F kdr mutation was identified in the para gene of the voltage-gated sodium channel (vgsc), along with its allelic and genotypic frequency. Low knockdown resistance (RRKC50) to deltamethrin was found in Puerto Colombia and Soledad populations as well as low resistance to λ-cyalothrin in this latter population. Moderate knockdown resistance to permethrin was found in both populations. At 24 h post-exposure on the other hand, there was low resistance (RRLC50) to permethrin in Puerto Colombia and moderate resistance in Soledad. Moderate resistance to deltamethrin was found in Puerto Colombia and low resistance in Soledad. Low resistance to λ-cyhalothrin was seen in Puerto Colombia and moderate resistance in Soledad. Variability was found in the susceptibility to the pyrethroids in the populations of Cx. quinquefasciatus evaluated, and the L1014F kdr mutation is reported for the first time as a possible pyrethroid resistance mechanism in this species in Colombia.