Mosquitoes cloak their legs to resist insecticides.

Vasileia Balabanidou,Mary Kefi,George Chalepakis,Hilary Ranson,Christoforos Nikolaou,Michalis Aivaliotis,Eva Papadogiorgaki,Venetia Koidou,M Patricia Juárez,Sergio J Mijailovsky,Anastasia Kampouraki,John Vontas,Juan R Girotti

doi:10.1098/rspb.2019.1091

Abstract

Malaria incidence has halved since the year 2000, with 80% of the reduction attributable to the use of insecticides. However, insecticide resistance is now widespread, is rapidly increasing in spectrum and intensity across Africa, and may be contributing to the increase of malaria incidence in 2018. The role of detoxification enzymes and target site mutations has been documented in the major malaria vector Anopheles gambiae; however, the emergence of striking resistant phenotypes suggests the occurrence of additional mechanisms. By comparing legs, the most relevant insect tissue for insecticide uptake, we show that resistant mosquitoes largely remodel their leg cuticles via enhanced deposition of cuticular proteins and chitin, corroborating a leg-thickening phenotype. Moreover, we show that resistant female mosquitoes seal their leg cuticles with higher total and different relative amounts of cuticular hydrocarbons, compared with susceptible ones. The structural and functional alterations in Anopheles female mosquito legs are associated with a reduced uptake of insecticides, substantially contributing to the resistance phenotype.

Highlights

Malaria is a life-threatening disease causing more than 500 000 deaths annually in sub-Saharan Africa, mostly in children under five and pregnant women
This study describes substantial differences in the properties of the insect cuticle in two strains of An. gambiae that differ in their insecticide resistance profile
These strains are from geographically distinct locations and have been maintained in colony for multiple years, the compelling evidence for quantitative differences in the cuticle both in the total amounts as well as in the relative amounts of certain components of the resistant strain used in this study is supportive of previous work demonstrating the importance of reduced penetration through the cuticle as a key resistance mechanism in An. gambiae

Summary

Introduction

Malaria is a life-threatening disease causing more than 500 000 deaths annually in sub-Saharan Africa, mostly in children under five and pregnant women. A multi-resistant An. gambiae mosquito strain from Co^te d’Ivoire (Tiassale) had a thicker femur cuticle (figure 1a), primarily due to enriched deposition of CHCs, which delayed the penetration rate of contact insecticides, and presumably produced a more intense and broader insecticide resistance phenotype [14,34]. The statistical analysis of cuticle thickness of both resistant and susceptible legs was performed by SPSS software tool v. To determine the differentially expressed peptides, we compared the abundances of the peptides between resistant and susceptible control mosquito legs, using a minimum of 3.0-fold changes (normalized to median). Legs and remaining bodies from both mosquito strains (susceptible and resistant) in three replicates of eight female mosquitoes, each 3–5 days old (48 legs each replicate), were mechanically homogenized and further processed for deacetylation of chitin to chitosan and determination of chitosan (i.e. glucosamine polymer). Mosquitoes’ leg and body weights were measured and used for normalization

Results

Discussion

Findings

42. Aivaliotis M et al 2007 Large-scale identification of