Co-occurrence of kdr mutations V1016I and F1534C in the voltage-gated sodium channel and their impact on the survivorship of Aedes aegypti (L.) (Diptera: Culicidae) from Harris County, Texas, after ULV Permanone ® (permethrin) field-cage tests.
Jonathan Hernandez and Patricia V. Pietrantonio
The yellow fever mosquito, Aedes aegypti (L.), is the principal vector of emerging human arboviruses which include dengue, yellow fever, Chikungunya, and Zika. Application of pyrethroids is the most often employed method for controlling mosquito populations during potential disease outbreaks. Heavy reliance on pyrethroids has caused a selection pressure that has led to the rapid increase of the knockdown resistance (kdr) mutations causative of resistance to pyrethroid-based insecticides. This resistance is caused by non‑synonymous mutations in the voltage‑gated sodium channel (vgsc) gene that result in single amino acid changes in the channel protein that reduce the affinity of the target site for insecticides; these mutations include V1016I and F1534C. To evaluate the potential impact of insecticide resistance on vector control, Ae. aegypti females were collected from two mosquito control operational areas in Harris County, Texas, and treated in separate field cage tests at three different distances with the pyrethroid Permanone® 31-66. The field tests included mosquitoes from the susceptible Orlando strain at each distance as positive controls. The females were then analyzed by melting curve analyses using allele-specific PCR primers to detect two kdr mutations (V1016I and F1534C) in the vgsc. At all distances from the treatment, the field collected mosquitoes had lower mortality than the insecticide-treated controls. Females from the Ae. aegypti susceptible Orlando strain, and from two operational areas that were placed at 7.62 m from the pyrethroid treatment, had the highest mortality within the tests, while more than half of the field-collected mosquitoes survived at 15.24 m, and at 22.86 m from the treatment source. We also found that both the V1016I and F1534C pyrethroid resistant mutations were present in Harris County at high frequency. Among Ae. aegypti that were analyzed (n=218), the double homozygous resistant mutant genotype (II/CC) was the most prevalent, followed by mosquitoes that had at least one resistant allele but were not double homozygous mutants; only a low percentage were homozygous susceptible wild-type (VV/FF). Our findings indicate an urgent need to re-evaluate insecticide resistance management in Harris County to develop more effective vector control strategies and tactics.