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Understanding the dynamics of insecticide resistance genes in mosquito populations is pivotal for a sustainable use of insecticides. Dieldrin resistance in Aedes albopictus is conferred by the alanine to serine substitution (A302S or RdlsupR/supallele) in the γ-aminobutyric acid (GABA) receptor encoded by the Rdl gene. On Reunion Island, dieldrin resistance was initially reported in natural Ae. albopictus populations sampled in 2008 despite the ban of dieldrin since 1994. To monitor insecticide resistance in Ae. albopictus on the island and to identify its drivers, we measured (i) the frequency of resistance alleles in 19 distinct natural populations collected between 2016 and 2017, (ii) fitness costs associated with dieldrin resistance in laboratory-controlled experiments, and (iii) the resistance conferred by RdlsupR/supto fipronil, an insecticide widely used on the island and reported to cross-react with RdlsupR/sup. The results show a persistence of RdlsupR/supin Ae. albopictus natural populations at low frequencies. Among the measured life history traits, mortality in pre-imaginal stages, adults' survival as well as the proportion of egg-laying females were significantly affected in resistant mosquitoes. Finally, bioassays revealed resistance of RdlsupR/supmosquitoes to fipronil, suggesting that the use of fipronil in natura could select for the RdlsupR/supallele. This study shows that dieldrin resistance is persistent in natural mosquito populations likely as a result of combined effects between fitness costs associated with RdlsupR/supand selection exerted by cross-reacting environmental insecticides such as fipronil.

International audience; Vector management is a cornerstone in the fight against vector-borne pathogens. However, the impact on ecosystem functioning of reducing or eliminating arthropod vector populations remains poorly understood. Vectors are members of complex ecological communities, and recent studies suggest that their population suppression alters food web dynamics (bottom-up and top-down trophic cascades), inter- and intraspecific competition, and plant pollination. Other possible overlooked roles are also proposed. In this review, with examples from vectors of plant, animal, and human pathogens, we highlight that, although the ecological roles of most vector species might be redundant with other non-vector species, changes in vector abundance alter biotic interactions and, thus, are unlikely to be neutral in terms of ecosystem functioning

BACKGROUND: Ivermectin is a potential new vector control tool to reduce malaria transmission. Mosquitoes feeding on a bloodmeal containing ivermectin have a reduced lifespan, meaning they are less likely to live long enough to complete sporogony and become infectious. We aimed to estimate the effect of ivermectin on malaria transmission in various scenarios of use.METHODS: We validated an existing population-level mathematical model of the effect of ivermectin mass drug administration (MDA) on the mosquito population and malaria transmission against two datasets: clinical data from a cluster- randomised trial done in Burkina Faso in 2015 wherein ivermectin was given to individuals taller than 90 cm and entomological data from a study of mosquito outcomes after ivermectin MDA for onchocerciasis or lymphatic filariasis in Burkina Faso, Senegal, and Liberia between 2008 and 2013. We extended the existing model to include a range of complementary malaria interventions (seasonal malaria chemoprevention and MDA with dihydroartemisinin-piperaquine) and to incorporate new data on higher doses of ivermectin with a longer mosquitocidal effect. We consider two ivermectin regimens: a single dose of 400 μg/kg (1 × 400 μg/kg) and three consecutive daily doses of 300 μg/kg per day (3 × 300 μg/kg). We simulated the effect of these two doses in a range of usage scenarios in different transmission settings (highly seasonal, seasonal, and perennial). We report percentage reductions in clinical incidence and slide prevalence.FINDINGS: We estimate that MDA with ivermectin will reduce prevalence and incidence and is most effective in areas with highly seasonal transmission. In a highly seasonal moderate transmission setting, three rounds of ivermectin only MDA at 3 × 300 μg/kg (rounds spaced 1 month apart) and 70% coverage is predicted to reduce clinical incidence by 71% and prevalence by 34%. We predict that adding ivermectin MDA to seasonal malaria chemoprevention in this setting would reduce clinical incidence by an additional 77% in children younger than 5 years compared with seasonal malaria chemoprevention alone; adding ivermectin MDA to MDA with dihydroartemisinin-piperaquine in this setting would reduce incidence by an additional 75% and prevalence by an additional 64% (all ages) compared with MDA with dihydroartemisinin-piperaquine alone.INTERPRETATION: Our modelling predictions suggest that ivermectin could be a valuable addition to the malaria control toolbox, both in areas with persistently high transmission where existing interventions are insufficient and in areas approaching elimination to prevent resurgence.FUNDING: Imperial College Junior Research Fellowship.

Additional file 1. Names of the I) diseases, II) pathogen agents, and III) vector species.

International audience; We investigated the genetic determinism of high chlorpyrifos resistance (HCR), a phenotype first described in 1999 in Culex pipiens mosquitoes surviving chlorpyrifos doses 1 mg l−1 and more recently found in field samples from Tunisia, Israel or Indian Ocean islands. Through chlorpyrifos selection, we selected several HCR strains that displayed over 10 000-fold resistance. All strains were homozygous for resistant alleles at two main loci: the ace-1 gene, with the resistant ace-1R allele expressing the insensitive G119S acetylcholinesterase, and a resistant allele of an unknown gene (named T) linked to the sex and ace-2 genes. We constructed a strain carrying only the T-resistant allele and studied its resistance characteristics. By crossing this strain with strains harboring different alleles at the ace-1 locus, we showed that the resistant ace-1R and the T alleles act in strong synergy, as they elicited a resistance 100 times higher than expected from a simple multiplicative effect. This effect was specific to chlorpyrifos and parathion and was not affected by synergists. We also examined how HCR was expressed in strains carrying other ace-1-resistant alleles, such as ace-1V or the duplicated ace-1D allele, currently spreading worldwide. We identified two major parameters that influenced the level of resistance: the number and the nature of the ace-1-resistant alleles and the number of T alleles. Our data fit a model that predicts that the T allele acts by decreasing chlorpyrifos concentration in the compartment targeted in insects.

International audience; While gene copy-number variations play major roles in long-term evolution, their early dynamics remains largely unknown. However, examples of their role in short-term adaptation are accumulating: identical repetitions of a locus (homogeneous duplications) can provide a quantitative advantage, while the association of differing alleles (heterogeneous duplications) allows carrying two functions simultaneously. Such duplications often result from rearrangements of sometimes relatively large chromosome fragments, and even when adaptive, they can be associated with dele-terious side effects that should, however, be reduced by subsequent evolution. Here, we took advantage of the unique model provided by the malaria mosquito Anopheles gambiae s.l. to investigate the early evolution of several duplications, heterogeneous and homogeneous, segregating in natural populations from West Africa. These duplications encompass ~200 kb and 11 genes, including the adaptive insecticide resistance ace-1 locus. Through the survey of several populations from three countries over 3-4 years, we showed that an internal deletion of all coamplified genes except ace-1 is currently spreading in West Africa and introgressing from An. gambiae s.s. to An. coluzzii. Both observations provide evidences of its selection, most likely due to reducing the gene-dosage disturbances caused by the excessive copies of the nona-daptive genes. Our study thus provides a unique example of the early adaptive tra-jectory of duplications and underlines the role of the environmental conditions (insecticide treatment practices and species ecology). It also emphasizes the striking diversity of adaptive responses in these mosquitoes and reveals a worrisome process of resistance/cost trade-off evolution that could impact the control of malaria vectors in Africa.

Control of infectious diseases is a major challenge of the century. Arthropod vectors are proliferating, leading to increasing prevalence of deadly diseases (e.g., malaria, dengue, and yellow fever). In several countries, particularly the poorest ones, vector control using insecticides is the only affordable way to fight these diseases. Unfortunately, resistance to these insecticides is often rapidly selected and is now widespread in many arthropod vectors. The general aim of this chapter is to provide a global overview of insecticide-resistance mechanisms and their evolution in disease vectors. Overall, it appears that some changes in the treatment strategies are urgently required to manage the development of insecticide resistance. This includes carefully using available insecticides, using alternative tools, and finally implicating the local communities in order to establish a continuous survey of resistance. Clearly, the greatest challenge for successful vector and disease control is the coordination of the different actors, despite their divergent agendas. Besides its implications in public health, insecticide resistance is a powerful model to study the evolution of adaptation; these fundamental approaches concurring to design new vector-control strategies.

International audience; Two amino acid substitutions in acetylcholinesterase 1 (AChE1), G119S and F290V, are responsible for resistance to organophosphate and carbamate insecticides in Culex pipiens mosquitoes. These mutations generate very different levels of insensitivity to insecticide inhibitors. We described here a biochemical method that rapidly identies AChE1 variants (susceptible, G119S and F290V, named S, R and V, respectively) present in individual mosquitoes. We investigated the frequency of AChE1 phenotypes in 41 eld samples collected around the Mediterranean Sea. F290V substitution was found only in 15 samples and at low frequency, whereas G119S was highly spread in all samples. However, seven V distinct alleles were identied whereas only one R allele was present. The [V] enzymatic phenotype was never observed alone, and the V allele was always found associated with the susceptible and/or G119S AChE1 ([VS], [VR] or [VRS] phenotypes). Furthermore, we showed the presence of duplicated alleles, associating a susceptible and a V copy of the ace-1 gene, in most individuals analyzed for its presence. Evolutionary forces driving the large number of F290V ace-1 alleles and their low frequency in Mediterranean countries are discussed.

BACKROUND: In Tetranychus urticae Koch, acetylcholinesterase insensitivity is often involved in organophosphate (OP) and carbamate (CARB) resistance. By combining toxicological, biochemical and molecular data from three reference laboratory and three OP selected strains (OP strains), the AChE1 mutations associated with resistance in T. urticae were characterised. RESULTS: The resistance ratios of the OP strains varied from 9 to 43 for pirimiphos-methyl, from 78 to 586 for chlorpyrifos, from 8 to 333 for methomyl and from 137 to 4164 for dimethoate. The insecticide concentration needed to inhibit 50% of the AChE1 activity was, in the OP strains, at least 2.7, 55, 58 and 31 times higher for the OP pirimiphos-methyl, chlorpyrifos oxon, paraoxon and omethoate respectively, and 87 times higher for the CARB carbaryl. By comparing the AChE1 sequence, four amino acid substitutions were detected in the OP strains: (1) F331W (Torpedo numbering) in all the three OP strains; (2) T280A found in the three OP strains but not in all clones; (3) G328A, found in two OP strains; (4) A201S found in only one OP strain. CONCLUSIONS: Four AChE1 mutations were found in resistant strains of T. urticae, and three of them, F331W, G328A and A201S, are possibly involved in resistance to OP and CARB insecticides. Among them, F331W is probably the most important and the most common in T. urticae. It can be easily detected by the diagnostic PCR-RLFP assay developed in this study. Copyright © 2009 Society of Chemical Industry

Background Ivermectin has been proposed as a novel malaria transmission control tool based on its insecticidal properties and unique route of acquisition through human blood. To maximize ivermectin’s effect and identify potential resistance/tolerance mechanisms, it is important to understand its effect on mosquito physiology and potential to shift mosquito population age-structure. We therefore investigated ivermectin susceptibility and gene expression changes in several age groups of female Anopheles gambiae mosquitoes. Methods The effect of aging on ivermectin susceptibility was analyzed in three age groups (2, 6, and 14-days) of colonized female Anopheles gambiae mosquitoes using standard survivorship assays. Gene expression patterns were then analyzed by transcriptome sequencing on an Illumina HiSeq 2500 platform. RT-qPCR was used to validate transcriptional changes and also to examine expression in a different, colonized strain and in wild mosquitoes, both of which blood fed naturally on an ivermectin-treated person. Results Mosquitoes of different ages and blood meal history died at different frequencies after ingesting ivermectin. Mortality was lowest in 2-day old mosquitoes exposed on their first blood meal and highest in 6-day old mosquitoes exposed on their second blood meal. Twenty-four hours following ivermectin ingestion, 101 and 187 genes were differentially-expressed relative to control blood-fed, in 2 and 6-day groups, respectively. Transcription patterns of select genes were similar in membrane-fed, colonized, and naturally-fed wild vectors. Transcripts from several unexpected functional classes were highly up-regulated, including Niemann-Pick Type C (NPC) genes, peritrophic matrix-associated genes, and immune-response genes, and these exhibited different transcription patterns between age groups, which may explain the observed susceptibility differences. Niemann-Pick Type 2 genes were the most highly up-regulated transcripts after ivermectin ingestion (up to 160 fold) and comparing phylogeny to transcriptional patterns revealed that NPCs have rapidly evolved and separate members respond to either blood meals or to ivermectin. Conclusion We present evidence of increased ivermectin susceptibility in older An. gambiae mosquitoes that had previously bloodfed. Differential expression analysis suggests complex midgut interactions resulting from ivermectin ingestion that likely involve blood meal digestion physiological responses, midgut microflora, and innate immune responses. Thus, the transcription of certain gene families is consistently affected by ivermectin ingestion, and may provide important clues to ivermectin’s broad effects on malaria vectors. These findings contribute to the growing understanding of ivermectin’s potential as a transmission control tool. Electronic supplementary material The online version of this article (doi:10.1186/s12864-015-2029-8) contains supplementary material, which is available to authorized users.

Organophosphate/carbamate target resistance has emerged in Culex pipiens L. (Diptera: Culicidae), the vector of Wuchereria bancrofti and West Nile virus (family Flaviviridae, genus Flavivirus) in China. The insensitive acetylcholinesterase was detected in only one of 20 samples collected on a north-to-south transect. According to previous findings, a unique mutation, G119S in the ace-1 gene, explained this high insensitivity. Phylogenetic analysis indicates that the mutation G119S recently detected in China results from an independent mutation event. The G119S mutation thus occurred at least three times independently within the Cx. pipiens complex, once in the temperate (Cx. p. pipiens) and twice in the tropical form (Cx. p. quinquefasciatus). Bioassays performed with a purified G119S strain indicated that this substitution was associated with high levels of resistance to chlorpyrifos, fenitrothion, malathion, and parathion, but low levels of resistance to dichlorvos, trichlorfon, and fenthion. Hence, it is possible that in China, dichlorvos, trichlorfon, and fenthion will still achieve effective control even in the presence of the G119S mutation.

It has recently been reported that the synaptic acetylcholinesterase (AChE) in mosquitoes is encoded by theace-1gene, distinct and divergent from theace-2gene, which performs this function inDrosophila. This is an unprecedented situation within the Diptera order because bothacegenes derive from an old duplication and are present in most insects and arthropods. Nevertheless,Drosophilapossesses only theace-2gene. Thus, a secondary loss occurred during the evolution of Diptera, implying a vital function switch from one gene (ace-1) to the other (ace-2). We sampled 78 species, representing 50 families (27% of the Dipteran families) spread over all major subdivisions of the Diptera, and looked forace-1andace-2by systematic PCR screening to determine which taxonomic groups within the Diptera have this gene change. We show that this loss probably extends to all true flies (or Cyclorrhapha), a large monophyletic group of the Diptera. We also show thatace-2plays a non-detectable role in the synaptic AChE in a lower Diptera species, suggesting that it has non-synaptic functions. A relative molecular evolution rate test showed that the intensity of purifying selection onace-2sequences is constant across the Diptera, irrespective of the presence or absence oface-1, confirming the evolutionary importance of non-synaptic functions for this gene. We discuss the evolutionary scenarios for the takeover oface-2and the loss oface-1, taking into account our limited knowledge of non-synaptic functions ofacegenes and some specific adaptations of true flies.

Recently there have been calls for the eradication of malaria and the elimination of soil-transmitted helminths (STHs). Malaria and STHs overlap in distribution, and STH infections are associated with increased risk for malaria. Indeed, there is evidence that suggests that STH infection may facilitate malaria transmission. Malaria and STH coinfection may exacerbate anemia, especially in pregnant women, leading to worsened child development and more adverse pregnancy outcomes than these diseases would cause on their own. Ivermectin mass drug administration (MDA) to humans for malaria parasite transmission suppression is being investigated as a potential malaria elimination tool. Adding albendazole to ivermectin MDAs would maximize effects against STHs. A proactive, integrated control platform that targets malaria and STHs would be extremely cost-effective and simultaneously reduce human suffering caused by multiple diseases. This paper outlines the benefits of adding albendazole to ivermectin MDAs for malaria parasite transmission suppression.

International audience; Resistance to insecticides has become a critical issue in pest management and it is particularly chronic in the control of human disease vectors. The gravity of this situation is being exacerbated since there has not been a new insecticide class produced for over twenty years. Reasoned strategies have been developed to limit resistance spread but have proven difficult to implement in the field. Here we propose a new conceptual strategy based on inhibitors that preferentially target mosquitoes already resistant to a currently used insecticide. Application of such inhibitors in rotation with the insecticide against which resistance has been selected initially is expected to restore vector control efficacy and reduce the odds of neo-resistance. We validated this strategy by screening for inhibitors of the G119S mutated acetylcholinesterase-1 (AChE1), which mediates insensitivity to the widely used organophosphates (OP) and carbamates (CX) insecticides. PyrimidineTrione Furan-substituted (PTF) compounds came out as best hits, acting biochemically as reversible and competitive inhibitors of mosquito AChE1 and preferentially inhibiting the mutated form, insensitive to OP and CX. PTF application in bioassays preferentially killed OP-resistant Culex pipiens and Anopheles gambiae larvae as a consequence of AChE1 inhibition. Modeling the evolution of frequencies of wild type and OP-insensitive AChE1 alleles in PTF-treated populations using the selectivity parameters estimated from bioassays predicts a rapid rise in the wild type allele frequency. This study identifies the first compound class that preferentially targets OP-resistant mosquitoes, thus restoring OP-susceptibility, which validates a new prospect of sustainable insecticide resistance management. Citation: Alout H, Labbé P, Berthomieu A, Djogbénou L, Leonetti J-P, et al. (2012) Novel AChE Inhibitors for Sustainable Insecticide Resistance Management. PLoS ONE 7(10): e47125.

International audience; The status of genes conferring resistance to organophosphate and carbamate insecticides has been examined in Culex pipiens pipiens mosquitoes sampled in Algeria. Presence of overproduced esterases was sporadic, but acetylcholinesterase-1 resistant alleles were observed in almost all samples. We focused our study on the AChE1 G119S substitution characterized in almost all samples, mostly at the heterozygous state. A genetic test revealed the presence of ace-1 duplication associating a susceptible and a resistant ace-1 copy. Molecular characterization showed a high occurrence of ace-1 duplication with six distinct duplicated alleles out of four samples. The inferred frequency of duplicated allele suggests that it is replacing the single resistant G119S allele. Finally, we discuss the mechanism at the origin of these duplicated haplotypes and their consequences on the management of insecticide resistance. (C) 2010 Elsevier Ltd. All rights reserved.

International audience; n natural populations of mosquitoes, high level of resistance to carbamates (CX) and organophosphates (OP) is provided by insensitive acetylcholinesterase (AChE1). Different alleles conferring resistance have been identified at the ace 1 locus. They differ from the wildtype by only one amino-acid Substitution. The comparison of the biochemical characteristics of mutated recombinant proteins and AChE1 in resistant mosquito extracts confirmed the role of each substitution in insensitivity. Selection of these different resistant alleles in field populations depends likely on the insecticides used locally. Theoretical modelling studies are initiated to develop novel strategies of mosquito control. (C) 2008 Elsevier Ireland Ltd. All rights reserved.