Insecticide resistance is mediated by multiple mechanisms in recently introduced Aedes aegypti from Madeira Island (Portugal)

Gonçalo Seixas,Carla Alexandra Sousa,José Luís Vicente,John Vontas,João Pinto,David Weetman,Linda Grigoraki,Ana Clara Silva,Audrey Lenhart

doi:10.1371/journal.pntd.0005799

Abstract

BackgroundAedes aegypti is a major mosquito vector of arboviruses, including dengue, chikungunya and Zika. In 2005, Ae. aegypti was identified for the first time in Madeira Island. Despite an initial insecticide-based vector control program, the species expanded throughout the Southern coast of the island, suggesting the presence of insecticide resistance. Here, we characterized the insecticide resistance status and the underlying mechanisms of two populations of Ae. aegypti from Madeira Island, Funchal and Paúl do Mar.Methodology/Principal findingsWHO susceptibility bioassays indicated resistance to cyfluthrin, permethrin, fenitrothion and bendiocarb. Use of synergists significantly increased mortality rates, and biochemical assays indicated elevated activities of detoxification enzymes, suggesting the importance of metabolic resistance. Microarray-based transcriptome analysis detected significant upregulation in both populations of nine cytochrome P450 oxidase genes (including four known pyrethroid metabolizing enzymes), the organophosphate metabolizer CCEae3a, Glutathione-S-transferases, and multiple putative cuticle proteins. Genotyping of knockdown resistance loci linked to pyrethroid resistance revealed fixation of the 1534C mutation, and presence with moderate frequencies of the V1016I mutation in each population.Conclusions/SignificanceSignificant resistance to three major insecticide classes (pyrethroid, carbamate and organophosphate) is present in Ae. aegypti from Madeira Island, and appears to be mediated by multiple mechanisms. Implementation of appropriate resistance management strategies including rotation of insecticides with alternative modes of action, and methods other than chemical-based vector control are strongly advised to delay or reverse the spread of resistance and achieve efficient control.

Highlights

Aedes aegypti (Linnaeus, 1762) is the most important vector of dengue, chikungunya and Zika viruses
Aedes aegypti from Funchal were found to be resistant to all insecticides tested (Fig 1A), with mortality rates ranging between 10.9% and 77.5%
Mortality rates increased significantly when females were exposed to one or both of the synergists before the insecticide, suggesting involvement of metabolic resistance (Fig 1A). This was evident for permethrin, after exposure to either piperonyl butoxide (PBO) or diethyl maleate (DEM), and for fenitrothion, for which complete restoration of susceptibility was attained with both synergists

Summary

Introduction

Aedes aegypti (Linnaeus, 1762) is the most important vector of dengue, chikungunya and Zika viruses. Control measures based on source reduction were soon implement together with insecticide spraying mainly with pyrethroid insecticides, and application of Bacillus thuringiensis israelensis (Bti) for larval control [6,7]. This insecticide-based strategy was applied only in Santa Luzia municipality of Funchal, during the years 2006–2008. Aedes aegypti is a major mosquito vector of arboviruses, including dengue, chikungunya and Zika. Despite an initial insecticide-based vector control program, the species expanded throughout the Southern coast of the island, suggesting the presence of insecticide resistance. We characterized the insecticide resistance status and the underlying mechanisms of two populations of Ae. aegypti from Madeira Island, Funchal and Paul do Mar.

Methods

Results

Discussion

Conclusion