Mathilde Gendrin

Culex mosquitoes of the subgenus Melanoconion Theobald, 1903 of the genus Culex Linnaeus, 1758 include numerous species recognized as vectors of viruses to humans. This subgenus is the most speciose among the entire mosquito fauna of the Americas. However, despite decades of taxonomic research, many species remain undiscovered, undescribed or misinterpreted, especially in the Amazonian biome. In this article, we provide the description of three new species of Culex (Melanoconion) collected in the northeastern Amazon forest of French Guiana. Culex (Mel.) naufragabilis sp. nov., Culex (Mel.) ripisylvus sp. nov. and Culex (Mel.) wayampi sp. nov. are described based on both morphological features of the male genitalia and DNA barcodes obtained from type specimens. These species are, respectively, morphologically closer to Culex (Mel.) brachiatus Hutchings & Sallum, 2008, Culex (Mel.) silvai Duret, 1968 and Culex (Mel.) creole Anduze, 1949b than to any other described species. Diagnostic characters to assist their identification are provided and their placement within the infrasubgeneric classification of the subgenus Melanoconion is discussed.

Mosquito larvae rely on a living microbiota for normal development because the microbiota supplies essential nutrients, particularly vitamins. Beyond vitamin provision, transcriptomic data suggest that the microbiota also supports other key nutritional processes. Here, we explored these roles by conducting a metabolomics analysis on Aedes aegypti third instar larvae following microbiota depletion. We sampled larvae and dissected guts 12 and 20 h post-decolonization, and analysed methanol-soluble metabolites using untargeted gas chromatography–mass spectrometry. Our findings reveal a pronounced impact of gut microbial presence on several metabolites involved in the tricarboxylic acid cycle and the uricolytic pathway. Germ-free larvae also had a lower quantity of cholesterol in their guts, and their long-chain fatty acid profile was altered in their guts and whole larvae. Sterols, including cholesterol, are essential precursors for the production of the molting hormone 20-hydroxyecdysone. We therefore tested how supplementing exogenous cholesterol affects the development of germ-free larvae. The effects proved to be highly concentration-dependent, ranging from a marginally significant increase in successful development to adulthood at low concentrations, to a pronounced developmental impairment at higher concentrations. Moreover, bacteria deficient in fatty acid beta-oxidation had a significantly lower ability to support larval development. Together, the observed alterations suggest that microbiota-deprived larvae exhibit a downregulation of metabolic processes related to energy production, nitrogen excretion, and sterol metabolism, likely due to the absence of microbiota-derived vitamins essential for these central metabolic functions. IMPORTANCE: Mosquito larvae depend on gut microbiota for normal growth because microbes supply essential nutrients, particularly B vitamins. To explore microbial roles beyond vitamin provision, we analysed metabolic changes in Aedes aegypti larvae after microbiota removal using gas chromatography-mass spectrometry. Germ-free larvae exhibited decreased levels of metabolites associated with the tricarboxylic acid cycle and uricolytic pathway, indicating a general slowdown in metabolic activity and nitrogen waste processing. Additionally, the absence of a microbiota affected cholesterol and fatty acid metabolism. To validate these findings, we found that supplementing germ-free larvae with low levels of cholesterol modestly improved their development. In contrast, larvae colonized with bacteria deficient in fatty acid metabolism exhibited significantly reduced developmental success. Overall, the findings show that removing the microbiota downregulates key metabolic pathways related to energy production, nitrogen excretion, and sterol metabolism, highlighting that bacterial vitamins and fatty acid degradation are vital for mosquito larval development and successful transformation into adults.

Reference strains of Aedes aegypti , reared over decades under laboratory conditions, are commonly used in research due to their consistency and ease of handling. While their use is relevant in terms of reproducibility between labs, complementary work on field-collected mosquitoes and their progeny is essential to capture biological and behavioral variations of natural populations. However, experimental set-ups optimized on reference strains are not always successful with field-derived mosquitoes; their lack of attraction to experimental blood meals is a recurrent issue. In this study, we evaluated methods to improve blood-feeding rate of field-derived mosquitoes from Cayenne (French Guiana), using the New Orleans reference strain as a control. We tested the impact of several blood-feeding systems for mosquitoes kept in a cage or in individual vials and adjusted starvation parameters. Individual mosquitoes offered a blood meal in lids of microtubes had the highest blood-feeding rate. For field-derived mosquitoes, starvation, or alternatively, provision of a 3% salt solution instead of the sugar solution, also consistently improved blood-feeding rate, with a minimal impact on survival. Our results may be helpful for establishment of new colonies, including in resource-limited settings, studies on fitness of field-derived mosquitoes and on experiments requiring individual level monitoring.

Malaria in South America remains a serious public health problem. Anopheles ( Nyssorhynchus ) darlingi is the most important malaria vector across tropical Latin America. Vector-targeted disease control efforts require a thorough understanding of mosquito demographic and evolutionary patterns. We present and analyze whole genomes of 1094 An. darlingi (median depth 18x) from six South American countries. We observe deep geographic population structure, high genetic diversity including 13 putative segregating inversions, and no evidence for sympatric cryptic taxa despite high interpopulation divergence. Strong signals of selection are plausibly driven by insecticides, especially on cytochrome P450 genes. Our results will facilitate effective mosquito surveillance and control while highlighting ongoing challenges that a diverse vector poses for malaria elimination in the Western hemisphere.

Mosquito larvae rely on a living microbiota for normal development because the microbiota supplies essential nutrients, particularly vitamins. Beyond vitamin provision, transcriptomic data suggest that the microbiota also supports other key nutritional processes. Here, we explored these roles by conducting a metabolomics analysis on Aedes aegypti third instar larvae following microbiota depletion. We sampled larvae and dissected guts 12- and 20-hours post-decolonization and analysed methanol-soluble metabolites using untargeted gas chromatography–mass spectrometry. Our findings reveal a pronounced impact of gut microbial presence on several metabolites involved in the tricarboxylic acid cycle and the uricolytic pathway. Germ-free larvae also had a lower quantity of cholesterol in guts and their long-chain fatty acid profile was altered in guts and whole larvae. Sterols, including cholesterol, are essential precursors for the production of the moulting hormone 20-hydroxyecdysone. We therefore tested how supplementing exogenous cholesterol affects the development of germ-free larvae. The effects proved to be highly concentration-dependent, ranging from a marginally significant increase in successful development to adulthood at low concentrations to a pronounced developmental impairment at higher concentrations. Moreover, bacteria deficient in fatty acids beta-oxidation had a significantly lower ability to support larval development. Together, the observed alterations suggest that microbiota-deprived larvae exhibit a downregulation of metabolic processes related to energy production, nitrogen excretion and sterol metabolism, likely due to the absence of microbiota-derived vitamins essential for these central metabolic functions. Importance: Mosquito larvae depend on gut microbiota for normal growth because microbes supply essential nutrients, particularly B vitamins. To explore microbial roles beyond vitamin provision, we analysed metabolic changes in Aedes aegypti larvae after microbiota removal using gas chromatography-mass spectrometry. Germ-free larvae exhibited decreased metabolites associated with the tricarboxylic acid cycle and uricolytic pathway, indicating a general slowdown in metabolic activity and nitrogen waste processing. Additionally, the absence of a microbiota affected cholesterol and fatty acid metabolism. To validate these findings, we found that supplementing germ-free larvae with low levels of cholesterol modestly improved their development. In contrast, larvae colonized with bacteria deficient in fatty acid metabolism exhibited significantly reduced developmental success. Overall, the findings show that removing the microbiota downregulates key metabolic pathways related to energy production, nitrogen excretion, and sterol metabolism, highlighting that bacterial vitamins and fatty acid degradation are vital for mosquito larval development and successful transformation into adults.

Wolbachia, an endosymbiotic bacterium infecting a wide array of invertebrates, has gained attention for its potential in vector control. Its capacity to colonise host populations primarily relies on vertical transmission and reproductive manipulation in arthropods. This endosymbiont is additionally mutualistic in some hosts, across several Wolbachia supergroups; notably, in nematodes and, as recently demonstrated, in planthoppers and bedbugs, it functions as an essential nutritional symbiont by providing vitamins to its host. Since mosquito larvae require microbe-derived nutrients for development, we investigated whether Wolbachia alone can support larval development in Culex quinquefasciatus mosquitoes. Our findings reveal that Wolbachia alone is insufficient to support larval development. Using transient colonisation with Escherichia coli , we developed a protocol to produce adult Culex quinquefasciatus mosquitoes harbouring Wolbachia only (germ-free ^Wol+ ). These results suggest that E. coli can support larval development in this species, which typically thrives in murky water; they also underscore the importance of extracellular microbes in larval growth. Furthermore, when Wolbachia infection was suppressed in germ-free ^Wol+ larvae using tetracycline treatment, we observed enhanced larval development, suggesting that Wolbachia acts as a metabolic parasite. In summary, this study opens the way for gnotobiology research in Culex quinquefasciatus and highlights the intricate interactions between Wolbachia and other members, which collectively influence mosquito development.

We present a genome assembly from an individual female Anopheles (Nyssorhynchus) aquasalis (a malaria mosquito; Arthropoda; Insecta; Diptera; Culicidae), from a wild population in French Guiana. The genome sequence is 177 megabases in span. The majority of the assembly is scaffolded into four chromosomal pseudomolecules with the X sex chromosome assembled into two arms, XR and XL. The complete mitochondrial genome was also assembled and is 15.4 kilobases in length.

Reference strains of Aedes aegypti , reared over numerous generations under laboratory conditions, are selected to fit laboratory conditions and commonly used in research due to their consistency and ease of handling. However, working exclusively with such strains may not fully reflect the traits of natural populations. While working on such strains is relevant in terms of reproducibility between labs, it is also important to perform some work on field-collected mosquitoes and their progeny to capture more representative biological and behavioural variation. In this study, we used the New Orleans reference strain as a control to adjust and evaluate methods to manipulate the F1 progeny of field-collected mosquitoes from Cayenne (French Guiana). To improve blood feeding rate, we tested the impact of several blood feeding systems for mosquitoes kept in a cage or in individual vials and adjusted starvation time. To monitor fertilization, we assessed if dissection buffer affects burst of spermatheca during dissection, whether mosquitoes were collected alive of shortly after death. The results described here may be helpful for studies on mosquito fitness, particularly on field-derived mosquitoes or on experiments requiring individual level monitoring. Author summary: Aedes aegypti is the major vector of dengue virus, causing hundreds of millions of cases per year. To fight against disease transmission, mosquitoes are studied in the laboratory, notably using colonies of mosquitoes kept over decades in the laboratory. These reference strains have been selected to fit laboratory conditions and may thus not fully reflect the traits of natural populations. While working on such strains is relevant in a sake of consistency between labs and ease of handling, it is also important to work on field-collected mosquitoes and their progeny to capture more representative biological and behavioural variation. In this study, we adjusted and evaluated methods to manipulate the F1 progeny of field-collected mosquitoes from Cayenne (French Guiana), using the New Orleans reference strain as a control. To improve blood feeding rate, we tested the impact of several blood feeding systems for mosquitoes kept in a cage or in individual vials and adjusted starvation time. To monitor fertilization, we assessed if dissection buffer affects burst of spermatheca during dissection, whether mosquitoes were collected alive of shortly after death. The results described here may be helpful for studies on mosquito fitness, particularly on field-derived mosquitoes or on experiments requiring individual level monitoring.

We present two genome assemblies, each generated from individual female Anopheles (Nyssorhynchus) darlingi (the malaria mosquito; Arthropoda; Insecta; Diptera; Culicidae), from wild populations in French Guiana and Peru. The genome sequences are approximately 180 megabases in span. The majority of each assembly is scaffolded into three chromosomal pseudomolecules with the X sex chromosome assembled. The complete mitochondrial genomes were also assembled and are both 15.4 kilobases in length. The assemblies differ by two inversions in chromosome arm 2R.

Wolbachia is an endosymbiotic bacterium infecting a wide array of invertebrates that gained attention for its potential to curb the transmission of vector-borne diseases. Its capacity to colonize arthropod populations is generally driven by vertical transmission and reproductive manipulation. In some insect species, Wolbachia additionally became an essential nutritional symbiont, providing vitamins to its host. As mosquito larvae require microbe-derived vitamins for development, we studied whether such a support of Wolbachia would exist in mosquitoes but be masked by the presence of other microbes. We chose Culex quinquefasciatus species to address this question, as it is highly colonized with Wolbachia . We developed a method to produce Culex quinquefasciatus devoid of extracellular microbiota and demonstrated that Wolbachia alone is insufficient to support larval development. Using transient colonization with Escherichia coli , we managed to produce adult Culex quinquefasciatus harboring Wolbachia only. When curbing Wolbachia infection of these E. coli -colonized larvae via tetracycline treatment, we obtained a higher larval development. Together, our data indicate that Wolbachia does not support development but rather acts here as a metabolic burden, and that E. coli is sufficient for development success even in a species that grows in “dirty” water. This opens the way towards gnotobiology studies in Culex quinquefasciatus and highlights the complex relationships between Wolbachia and its mosquito host. Author summary: Wolbachia is a bacterium infecting many invertebrates that gained attention for its potential to curb the transmission of vector-borne diseases, such as dengue. In some insect species, Wolbachia provides vitamins to its host. As mosquito larvae require microbe-derived vitamins for development, we studied whether such a support of Wolbachia would exist in mosquitoes but be masked by the presence of other microbes. We chose Culex quinquefasciatus species to address this question, as it is highly colonized with Wolbachia . We developed a method to produce Culex quinquefasciatus devoid of extracellular microbiota and demonstrated that Wolbachia alone is insufficient to support larval development. We transiently colonized these larvae with Escherichia coli to rescue larval development and to produce adults harboring Wolbachia only. When curbing Wolbachia infection of these E. coli -colonized larvae via tetracycline treatment, we obtained a higher larval development. Together, our data indicate that Wolbachia does not support development but rather acts here as a metabolic burden, and that E. coli is sufficient for development success even in a mosquito species that grows in “dirty” water.