Mutations in the voltage-gated sodium channel associated with pyrethroid resistance in Aedes albopictus in Yucatan, Mexico

Abstract

Aedes albopictus (Skuse) is a competent vector of dengue and Zika viruses in Mexico. Monitoring the level of resistance of local population is essential due to its epidemiological significance. This study aimed to identify mutations in the voltage-gated sodium channel (VGSC) as one of the mechanisms responsible for pyrethroid insecticide resistance in Ae. albopictus. Immature samples were collected in a rural town in Yucatan, Mexico, from May to October 2021. The pyrethroid insecticide lambda-cyhalothrin was impregnated in CDC bottles and bioassays were conducted on Ae. albopictus populations 3-5 days after emergence. The mosquitoes were susceptible to the insecticide. Females were taken for total DNA extraction. Fragments of domains II, III, and IV of the voltage-gated sodium channel (VGSC) were amplified and sequenced. The presence of synonymous and non-synonymous mutations was found in positions 1532 and 1534 of domain III of the sodium channel gene (VGSC). No mutant alleles in domain IV were detected. A homozygous mutant (ACG) coding for the amino acid threonine (1008Thr) was identified in domain II. Domain III included three heterozygous alleles (P1528S, L1530S, and Ile1410Thr). This last heterozygous allele is reported for the first time in Mexico. Homozygous mutants encoding the amino acids serine/serine and serine/proline in domain III were observed. These have been reported in Aedes aegypti from Mexico, but not yet in Ae. albopictus. This represents new findings for the region, as Ae. albopictus has only been introduced there for approximately five years. In conclusion, non-synonymous mutations were found in Ae. albopictus in a rural area of Yucatan, emphasizing the importance of integrated vector control to prevent Asian tiger mosquitoes from spreading these resistant alleles.

Figure 1. Amplification of partial sequences of the voltage-gated sodium channel (VGSC) domains in Ae. albopictus, the target of action of pyrethroid insecticides. LI MWM: 1500 bp molecular weight marker (ThermoFisher Scientific); L2DIII and L3DIII: partial amplified segment of Domain III (740 bp); L4DII and L5DII: partial amplified segment of Domain II (480 bp); L6DIV and L7DIV: partial amplified segment of Domain IV (280 bp); and L8C-: negative control.

Figure 2. Chromatogram of mutations identified in partial segments of Domain II (480bp) and Domain III (740bp) of the sodium channel gene in Ae. albopictus populations. Red letters correspond to the substituted nucleotides.