Characterization of Sodium Channel Mutations in the Dengue Vector Mosquitoes Aedes aegypti and Aedes albopictus within the Context of Ongoing Wolbachia Releases in Kuala Lumpur, Malaysia.

Noor Afizah Ahmad,Yoon Ling Cheong,Siti Nor Syazwani Amran,Mohd Arif Abdul Karim,Nur Ruqqayah Mohd Mazni,Muhammad Kamarul Ridhuan Ghazali,Ary A Hoffmann,Nancy M Endersby-Harshman,Steven P Sinkins,Nur Zatil Aqmar Mohd Zabari,Nazni Wasi Ahmad

doi:10.3390/insects11080529

Abstract

Specific sodium channel gene mutations confer target site resistance to pyrethroid insecticides in mosquitoes and other insects. In Aedes mosquito species, multiple mutations that contribute to resistance vary in their importance around the world. Here, we characterize voltage sensitive sodium channel (Vssc) mutations in populations of Aedesaegypti from Kuala Lumpur, Malaysia, and look at their persistence in populations affected by ongoing Wolbachia releases (a dengue control measure). We also describe a Vssc mutation in Aedesalbopictus (F1534L) found for the first time in Malaysia. We show that there are three predominant Vssc haplotypes in Aedesaegypti in this region, which all persist with regular backcrossing, thereby maintaining the original genetic composition of the populations. We identify changes in genotype frequency in closed populations of Ae. aegypti maintained for multiple generations in laboratory culture, suggesting different fitness costs associated with the genotypes, some of which may be associated with the sex of the mosquito. Following population replacement of Ae. aegypti by Wolbachia in the target area, however, we find that the Vssc mutations have persisted at pre-release levels. Mosquitoes in two genotype classes demonstrate a type I pyrethroid resistance advantage over wildtype mosquitoes when exposed to 0.25% permethrin. This resistance advantage is even more pronounced with a type II pyrethroid, deltamethrin (0.03%). The results point to the importance of these mutations in pyrethroid resistance in mosquito populations and the need for regular backcrossing with male mosquitoes from the field to maintain similarity of genetic background and population integrity during Wolbachia releases.

Highlights

IntroductionMalaysia is one of the most affected countries, with a total of 130,101 dengue cases and 182 deaths being recorded for 2019
Dengue is a mosquito-borne infection that has become a major international public health concern.Malaysia is one of the most affected countries, with a total of 130,101 dengue cases and 182 deaths being recorded for 2019
Adult female Ae. aegypti from the field strain collected at Shah Alam without Wolbachia and tested at the F1–F3 generations were highly resistant to 0.25% permethrin delivered on impregnated filter papers in WHO diagnostic dose bioassays as reflected by a low mortality, the mean mortality did tend to vary across generations (Figure 2a)

Summary

Introduction

Malaysia is one of the most affected countries, with a total of 130,101 dengue cases and 182 deaths being recorded for 2019. This reflects an increase of 61.4% in terms of dengue cases and 23.8% in terms of deaths as compared to a similar period in 2018 [1]. In Malaysia, reducing human cases of dengue still relies on the control of vector mosquitoes, through fogging using permethrin, deltamethrin and malathion to kill adult mosquitoes, and larviciding using temephos to kill larvae. In Malaysia, selection for insecticide resistance in Aedes species likely began with fogging operations using malathion which has continued since the early 1970s, and fogging with permethrin which has occurred since early 1996 [5]. Regular indoor residual spraying with dichlorodiphenyltrichloroethane (DDT) was undertaken in Malaysia for 26 years, which switched to deltamethrin in 1997 [6]

Methods

Results

Discussion

Conclusion