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International audience; The Culex pipiens mosquito complex is a group of evolutionarily closely related species including C. pipiens and Culex quinquefasciatus, both infected by the cytoplasmically inherited Wolbachia symbiont. A Wolbachia-uninfected population of C. pipiens was however described in South Africa and was recently proposed to represent a cryptic species. In this study, we reconsidered the existence of this species by undertaking an extensive screening for the presence of Wolbachia-uninfected C. pipiens specimens and by characterizing their genetic relatedness with known members of the complex. We first report on the presence of Wolbachia-uninfected specimens in several breeding sites. We next confirm that these uninfected specimens unambiguously belong to the C. pipiens complex. Remarkably, all uninfected specimens harbour mitochondrial haplotypes that are either novel or identical to those previously found in South Africa. In all cases, these mitochondrial haplotypes are closely related, but different, to those found in other C. pipiens complex members known to be infected by Wolbachia. Altogether, these results corroborate the presence of a widespread cryptic species within the C. pipiens species complex. The potential role of this cryptic C. pipiens species in the transmission of pathogens remains however to be determined. The designation 'Culex juppi nov. sp.' is proposed for this mosquito species.

Background: Insecticide resistance is a rapid and recent evolutionary phenomenon with serious economic and public health implications. In the mosquito Anopheles gambiae s.s., main vector of malaria, resistance to organophosphates and carbamates is mainly due to a single amino-acid substitution in acetylcholinesterase 1 (AChE1). This mutation entails a large fitness cost. However, a resistant duplicated allele of the gene encoding AChEI (ace-1), potentially associated to a lower fitness cost, recently appeared in An. gambiae. Methods: Using molecular phenotype data collected from natural populations from West Africa, the frequency of this duplicated allele was investigated by statistical inference. This method is based on the departure from Hardy-Weinberg phenotypic frequency equilibrium caused by the presence of this new allele. Results: The duplicated allele, Ag-ace-1(D), reaches a frequency up to 0.65 in Ivory Coast and Burkina Faso, and is potentially present in Benin. A previous study showed that Ag-ace-1(D), present in both M and S molecular forms in different West Africa countries, was generated by a single genetic event. This single origin and its present distribution suggest that this new allele is currently spreading. Conclusion: The spread of this less costly resistance allele could represent a major threat to public health, as it may impede An. gambiae control strategies, and thus increases the risk of malaria outbreaks.

Le Languedoc-Roussillon présente des caractéristiques particulières ou un niveau particulier de risques: le vieillissement de la population, particulièrement évident dans la région, ainsi que l'augmentation de la population en situation précaire posent des problèmes de nutrition et de prise en charge. L'alimentation de type méditerranéen, dont les bienfaits pour la santé sont reconnus, est progressivement remplacée par une alimentation mondialisée, standardisée et peu variée, ce qui entraîne, avec le développement de la sédentarité, une épidémie d'obésité/diabète avec, entre autres, des conséquences cardio-vasculaires. Parmi les maladies émergentes, il faut noter certaines formes de cancer, des maladies neuro-dégénératives (Alzheimer), et nombre de maladies infectieuses et parasitaires qui, du fait des échanges constants avec la région, risquent de se développer, les vecteurs ou réservoirs étant présents sur notre territoire. Une réflexion des responsables locaux et de la population est nécessaire.

International audience

Anopheles gambiae$ s.s. is a complex of sibling taxa characterized by various paracentric inversions. In west and central Africa, where several taxa are sympatric, a kdr mutation responsible for pyrethroid resistance has been described in only one (the S taxon), suggesting an absence of gene flow between them. Following a thorough sampling, we have found a kdr mutation in another taxon (M). To establish whether this mutation is the same event or not, the large intron upstream of the kdr mutation was sequenced to find polymorphic sites in suceptible/resistant and M/S mosquitoes. The low genetic diversity found in this DNA region indicates that a local genetic sweep has recently occured. However, some polymorphic sites were found, and it is therefore concluded that the kdr mutation in the M taxon is not an independent mutation event, and is best explained by an introgression from the S taxon. These results are discussed whithin the context of possible gene flow between members of #An. gambiae$ s.s. taxa, and with the possible spread of the kdr mutation in other closely related malaria vectors of the #An. gambiae$ complex. (Résumé d'auteur)

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International audience; In Culex pipiens mosquitoes, resistance to organophosphorous insecticides often results from increased detoxification by two types of esterases, A and B, which are closely linked. Overproduction of all esterases B so far investigated (B1, B2, B4, B5 and B6) is from gene amplification. An esterase A gene (esterase A2) has recently been cloned from mosquitoes with the overproduced esterases A2 and B2, and amplification of this gene has also been reported. We describe the cDNA sequences of three additional esterase genes from insecticide-resistant strains of Culex pipiens originating from France and California which show at least 93 per cent homology with the esterase A2 gene sequence. Restriction enzyme mapping shows that the esterase A gene lies within 2.2 kb of the esterase B gene. In mosquitoes with overproduced esterases A2 and B2, the amplification level of esterase A is equal to that of esterase B suggesting that the genes are coamplified. Furthermore, we show that in one strain with an overproduced A esterase (A1), gene amplification cannot account for the increased protein level. This indicates that overproduction of esterases A can be achieved through two different mechanisms: gene amplification and a regulatory mechanism - the nature of which remains to be identified.

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Larval susceptibility to organophosphates (OP), carbamates (CARB) and pyrethroids (PYR) was investigated in #Culex quinquefasciatus$ from Côte d'Ivoire and Burkina Faso. A total of 33 populations collected in 25 cities were tested. The resistance of these natural field populations was compared to a susceptible reference strain under the same conditions. In Côte d'Ivoire, populations showed a heterogeneous response to OP and CARB. A range of 40 %-98 % of larvae had a low resistance level to both chlorpyrifos (2-8x) and propoxur (1-4x). The remaining 2 % to 60 % of larvae displayed a high level of cross-resistance between chlorpyrifos (15-30x) and propoxur (>700x). Biochemical studies showed that low level resistance to OP was due to A2-B2 overproduced esterases and that cross-resistance to OP and CARB was conferred by an insensitive acetylcholinesterase (AChE). This AChE provided a lower resistance to temephos (10x). In Burkina Faso, populations were slightly resistant to OP (1-3x) and not to CARB. The esterases A2-B2 were only present at 50 % frequency. In contrast, PYR-resistance was similar between the two countries. All populations were resistant to either permethrin (20-80x) and deltamethrin (15-40x). Bioassays using piperonyl butoxide (PB) and biochemical studies showed that PYR-resistance involved increased metabolism by mixed function oxidases. Knowing that synergism of PB did not completely suppress resistance and that adults did not show a knockdown effect with high permethrin concentrations, it is likely that PYR-resistance was also due to a Kdr gene. (Résumé d'auteur)

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International audience; In recent years the incidence of dengue fever epidemics has increased and transmission has tended to be established over a geographically expanding area, including French Polynesia. An increase in air transportation contributes to the diffusion of the dengue virus from Southeast Asia, a region considered to be a hyperendemic dengue zone, to the Pacific region. Presently, little is known about the role of the vector (Aedes aegypti) in the diffusion of the dengue fever virus. A study on the genetic structure of vector populations was conducted using allozyme polymorphism. This study showed a low level of genetic exchange between mosquito populations on different islands. It is concluded that the occurrence of dengue hemorrhagic fever in French Polynesia during the last few years was likely due to the dispersal of the dengue virus via viremic people rather than via infected vectors.

International audience