Genetic diversity of Culex pipiens mosquitoes in distinct populations from Europe: contribution of Cx. quinquefasciatus in Mediterranean populations

Culex-Transmitted Diseases: Mechanisms, Impact, and Future Control Strategies using Wolbachia

Mosquitoes of the Culex genus are responsible for a large burden of zoonotic virus transmission globally. Collectively, they play a significant role in the transmission of medically significant diseases such as Japanese encephalitis virus and West Nile virus. Climate change, global trade, habitat transformation and increased urbanisation are leading to the establishment of Culex mosquitoes in new geographical regions. These novel mosquito incursions are intensifying concerns about the emergence of Culex-transmitted diseases and outbreaks in previously unaffected areas. New mosquito control methods are currently being developed and deployed globally. Understanding the complex interaction between pathogens and mosquitoes is essential for developing new control strategies for Culex species mosquitoes. This article reviews the role of Culex mosquitos as vectors of zoonotic disease, discussing the transmission of viruses across different species, and the potential use of Wolbachia technologies to control disease spread. By leveraging the insights gained from recent successful field trials of Wolbachia against Aedes-borne diseases, we comprehensively discuss the feasibility of using this technique to control Culex mosquitoes and the potential for the development of next generational Wolbachia-based control methods.

A DNA barcode reference library of Croatian mosquitoes (Diptera: Culicidae): implications for identification and delimitation of species, with notes on the distribution of potential vector species

BACKGROUND

Mosquitoes pose a risk to human health worldwide, and correct species identification and detection of cryptic species are the most important keys for surveillance and control of mosquito vectors. In addition to traditional identification based on morphology, DNA barcoding has recently been widely used as a complementary tool for reliable identification of mosquito species. The main objective of this study was to create a reference DNA barcode library for the Croatian mosquito fauna, which should contribute to more accurate and faster identification of species, including cryptic species, and recognition of relevant vector species.

METHODS

Sampling was carried out in three biogeographical regions of Croatia over six years (2017-2022). The mosquitoes were morphologically identified; molecular identification was based on the standard barcoding region of the mitochondrial COI gene and the nuclear ITS2 region, the latter to identify species within the Anopheles maculipennis complex. The BIN-RESL algorithm assigned the COI sequences to the corresponding BINs (Barcode Index Number clusters) in BOLD, i.e. to putative MOTUs (Molecular Operational Taxonomic Units). The bPTP and ASAP species delimitation methods were applied to the genus datasets in order to verify/confirm the assignment of specimens to specific MOTUs.

RESULTS

A total of 405 mosquito specimens belonging to six genera and 30 morphospecies were collected and processed. Species delimitation methods assigned the samples to 31 (BIN-RESL), 30 (bPTP) and 28 (ASAP) MOTUs, with most delimited MOTUs matching the morphological identification. Some species of the genera Culex, Aedes and Anopheles were assigned to the same MOTUs, especially species that are difficult to distinguish morphologically and/or represent species complexes. In total, COI barcode sequences for 34 mosquito species and ITS2 sequences for three species of the genus Anopheles were added to the mosquito sequence database for Croatia, including one individual from the Intrudens Group, which represents a new record for the Croatian mosquito fauna.

CONCLUSION

We present the results of the first comprehensive study combining morphological and molecular identification of most mosquito species present in Croatia, including several invasive and vector species. With the exception of some closely related species, this study confirmed that DNA barcoding based on COI provides a reliable basis for the identification of mosquito species in Croatia.

Mitochondrial and microbial diversity of the invasive mosquito vector species Culex tritaeniorhynchus across its extensive inter-continental geographic range

Background

Culex (Cx.) tritaeniorhynchus is an invasive mosquito species with an extensive and expanding inter-continental distribution, currently reported across Asia, Africa, the Middle East, Europe and now Australia. It is an important vector of medical and veterinary pathogens which cause significant morbidity and mortality in human and animal populations. Across regions endemic for Japanese encephalitis virus (JEV), Cx. tritaeniorhynchus is considered the major vector and has also been shown to contribute to the transmission of several other zoonotic arboviruses including Rift Valley fever virus (RVFV) and West Nile virus (WNV).

Methods

In this study, we used laboratory vector competence experiments to determine if Cx. tritaeniorhynchus from a Southern European population were competent JEV vectors. We also obtained samples from multiple geographically dispersed Cx. tritaeniorhynchus populations from countries within Europe, Africa, Eurasia and Asia to perform phylogenetic analysis to measure the level of mitochondrial divergence using the cytochrome oxidase subunit 1 ( CO1) gene. We also undertook bacterial 16S rRNA gene amplicon sequencing to determine microbial diversity and used multi-locus sequence typing (MLST) to determine any evidence for the presence of strains of the naturally occurring endosymbiotic bacterium Wolbachia.

Results

Cx. tritaeniorhynchus from a Greek population were shown be be competent vectors of JEV with high levels of virus present in saliva. We found a signficant level of mitochondrial genetic diversity using the mosquito CO1 gene between geographically dispersed populations. Furthermore, we report diverse microbiomes identified by 16S rRNA gene amplicon sequencing within and between geographical populations. Evidence for the detection of the endosymbiotic bacteria Wolbachia was confirmed using Wolbachia-specific PCR and MLST.

Conclusions

This study enhances our understanding of the diversity of Cx. tritaeniorhynchus and the associated microbiome across its inter-continental range and highlights the need for greater surveillance of this invasive vector species in Europe.

Unraveling biotypes of the northern house mosquito, Culex pipiens s.l. (Diptera: Culicidae): molecular differentiation and morphometric analysis

Geometric morphometrics was used to determine whether geographic isolation could explain differences in wing size and shape between and within continental (27°S to 41°S) and insular (Rapa Nui) populations of Culex pipiens s.s. Linnaeus and their biotypes (f. pipiens and f. molestus). Molecular protocols based on polymorphisms in the second intron of nuclear locus ace-2 (acetylcholinesterase-2) were used to differentiate Cx. pipiens s.s. from Cx. quinquefasciatus Say, and an assay based on polymorphisms in the flanking region of a microsatellite locus (CQ11) was used to identify biotypes. Culex pipiens f. molestus and hybrids shared larval habitats in all continental sites, while Cx. pipiens f. pipiens was found in 5 of the 10 sites. Only biotype molestus was found in Rapa Nui (Easter Island) Pipiens and molestus biotypes occur sympatrically in aboveground locations, and only molestus was found in the underground site (ME). Biotype molestus was dominant in rural locations and preferably anthropophilic. These results agree with the ecological descriptions previously reported for the biotypes of Cx. pipiens s.s. Procrustes ANOVA only showed differences in centroid size between biotypes in females and males and did not show significant differences in wing shape. However, we found significant differences among the geographic areas in the centroid size and wing shape of both females and males. Particularly, the population of Rapa Nui Island had shorter wings than the continental populations. The results highlight the effects of geographic and environmental processes on morphotypes in vector mosquitoes.

Applicability evaluation of mtDNA based molecular identification in mosquito species/subspecies/biotypes collected from Thessaloniki, Greece

The genus Culex, containing many described species, plays a role as a vector for diseases of medical and veterinary importance worldwide. Among these species, Culex pipiens is one of the most widespread mosquitoes and is classified into two biological forms (biotypes), named as Culex pipiens pipiens and Culex pipiens molestus. Due to similar morphological structure between these biotypes, morphological identification is inadequate. Thus, molecular methods have been developed and are considered more reliable, some of which are based on analyses of mitochondrial DNA. The aim of the present study was to evaluate the applicability and reliability of mtDNA based molecular identification methodologies. Initially, mosquito specimens (n = 100) collected from Thessaloniki, Greece were morphologically analyzed. Then, mitochondrial cox1 sequencing and PCR-RFLP methods were used to confirm the morphological identification results as well as to discriminate species and subspecies/biotype of Culex pipiens complex. According to morphological identification results, Culex pipiens complex (n = 92), Culex modestus (n = 6) and Culex theileri (n = 2) were detected. Using mtDNA sequencing, all Culex modestus and Culex theileri samples were confirmed whereas 86 of Culex pipiens complex were detected as Culex pipiens but surprisingly the remaining six of them were detected as Culex quinquefasciatus. Among Culex pipiens specimens, PCR-RFLP detected that frequency of Culex pipiens pipiens (85%; 85/100) was very high compared to Culex pipiens molestus (1%, 1/100). In conclusion, this study shows the necessity of use of molecular methods beside morphological methods for especially specimens detected as Culex pipiens. Also, it was shown that mtDNA PCR-RFLP methodology represents a well-established alternative for Culex biotypes identification.

Mosquitoes and Mosquito-Borne Diseases in Vietnam

Mosquito-borne diseases pose a significant threat to humans in almost every part of the world. Key factors such as global warming, climatic conditions, rapid urbanisation, frequent human relocation, and widespread deforestation significantly increase the number of mosquitoes and mosquito-borne diseases in Vietnam, and elsewhere around the world. In southeast Asia, and notably in Vietnam, national mosquito control programmes contribute to reducing the risk of mosquito-borne disease transmission, however, malaria and dengue remain a threat to public health. The aim of our review is to provide a complete checklist of all Vietnamese mosquitoes that have been recognised, as well as an overview of mosquito-borne diseases in Vietnam. A total of 281 mosquito species of 42 subgenera and 22 genera exist in Vietnam. Of those, Anopheles, Aedes, and Culex are found to be potential vectors for mosquito-borne diseases. Major mosquito-borne diseases in high-incidence areas of Vietnam include malaria, dengue, and Japanese encephalitis. This review may be useful to entomological researchers for future surveys of Vietnamese mosquitoes and to decision-makers responsible for vector control tactics.

Morphological and Molecular Characterization Using Genitalia and CoxI Barcode Sequence Analysis of Afrotropical Mosquitoes with Arbovirus Vector Potential

Potential arboviral Afrotropical mosquito vectors are underrepresented in public databases of CoxI barcode sequences. Furthermore, available CoxI sequences for many species are often not associated with voucher specimens to match the corresponding fine morphological characterization of specimens. Hence, this study focused on the characterization of Culicine mosquitoes from South Africa, Mozambique, and Angola and their classification using a complementary approach including a morphological analysis of specimens’ genitalia and phylogenetic study based on the analysis of CoxI barcode sequences using maximum likelihood and Bayesian phylogenetic inference methods, alongside Median-Joining Network and PCOORD analyses. Overall, 800 mosquitoes (652 males and 148 females) from 67 species, were analyzed. Genitalia from 663 specimens allowed the identification of 55 species of 10 genera. A total of 247 CoxI partial gene sequences corresponding to 65 species were obtained, 11 of which (Aedes capensis, Ae. mucidus, Culex andersoni, Cx. telesilla, Cx. inconspicuosus, Eretmapodites subsimplicipes, Er. quinquevittatus, Ficalbia uniformis, Mimomyia hispida, Uranotaenia alboabdominalis, and Ur. mashonaensis) are, to the best of our knowledge, provided here for the first time. The presence of Cx. pipiens ecotypes molestus and pipiens and their hybrids, as well as Cx. infula, is newly reported in the Afrotropical region. The rates of correct sequence identification using BOLD and BLASTn (≥95% identity) were 64% and 53%, respectively. Phylogenetic analysis revealed that, except for subgenus Eumelanomyia of Culex, there was support for tribes Aedini, Culicini, Ficalbiini, and Mansoniini. A divergence >2% was observed in conspecific sequences, e.g., Aedeomyia africana, Ae. cumminsii, Ae. unilineatus, Ae. metallicus, Ae. furcifer, Ae. caballus, and Mansonia uniformis. Conversely, sequences from groups and species complexes, namely, Ae. simpsoni, Ae. mcintoshi, Cx. bitaeniorhynchus, Cx. simpsoni, and Cx. pipiens were insufficiently separated. A contribution has been made to the barcode library of Afrotropical mosquitoes with associated genitalia morphological identifications.

Mosquito Vectors (Diptera: Culicidae) and Mosquito-Borne Diseases in North Africa

Mosquitoes (Diptera: Culicidae) are of significant public health importance because of their ability to transmit major diseases to humans and animals, and are considered as the world's most deadly arthropods. In recent decades, climate change and globalization have promoted mosquito-borne diseases' (MBDs) geographic expansion to new areas, such as North African countries, where some of these MBDs were unusual or even unknown. In this review, we summarize the latest data on mosquito vector species distribution and MBDs affecting both human and animals in North Africa, in order to better understand the risks associated with the introduction of new invasive mosquito species such as Aedes albopictus. Currently, 26 mosquito species confirmed as pathogen vectors occur in North Africa, including Aedes (five species), Culex (eight species), Culiseta (one species) and Anopheles (12 species). These 26 species are involved in the circulation of seven MBDs in North Africa, including two parasitic infections (malaria and filariasis) and five viral infections (WNV, RVF, DENV, SINV and USUV). No bacterial diseases have been reported so far in this area. This review may guide research studies to fill the data gaps, as well as helping with developing effective vector surveillance and controlling strategies by concerned institutions in different involved countries, leading to cooperative and coordinate vector control measures.

Landscape Composition Affects Elements of Metacommunity Structure for Culicidae Across South-Eastern Illinois

The interplay among invasive alien vectors and the species assemblage of native potential vectors in areas of range expansion may affect the dynamics of pathogen transmission. In this study we investigate how Aedes albopictus, an invasive mosquito of considerable public health concern fits within mosquito communities at the edge of its range of distribution. This was addressed using a 2-year field survey of mosquitoes in south-eastern Illinois. We found that Ae. albopictus was more broadly distributed in this region than previously realized, with new occurrence records for nine counties. Abundance of this species varied strongly and peaked in locations of low-intermediate overall mosquito species richness. This differed from overall mosquito abundance, as well as abundance of another important vector, Cx. pipiens, for which the abundance-richness relationships were best described with power functions. Metacommunity analyses revealed that mosquito communities showed a non-random distribution with a Clementsian gradient, which suggests a pattern whereby distinct species assemblages are associated with specific habitats or environmental conditions. Land use was a significant underlying factor shaping mosquito community structure and species assemblages. Multivariate analyses showed that while Ae. canadensis and Cx. pipiens complex mosquitoes were associated with high and low proportions of wetlands in the environment, respectively, Ae. albopictus was most strongly associated with urban settlements. This work sheds light on landscape-level processes, such as niche differentiation driven by urban and agricultural development, structuring mosquito communities. We suggest that mosquito community assessments across habitats be incorporated as part of a One Health vector surveillance approach to aid in the goal of prediction and prevention of new and (re-)emerging vector-borne diseases.

MALDI-TOF mass spectrometry identification of mosquitoes collected in Vietnam

BACKGROUND

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a tool that has revolutionised clinical microbiology and has recently been described as an innovative and effective approach to arthropod identification.

METHODS

In this study, mosquitoes were captured in Vietnam using four different methods (human landing catch, CDC light traps, BG-Sentinel traps, animal-baited net traps). A total of 4215 mosquitoes were captured and morphologically identified as belonging to three genera: Aedes, Anopheles and Culex. We randomly selected 1253 mosquitoes, including 662 specimens of 14 Anopheles species, 200 specimens of two Aedes species and 391 morphologically unidentified Culex specimens, for molecular and MALDI-TOF MS analysis. The DNA from 98 mosquitoes (69 Anopheles specimens, 23 Culex specimens and six Aedes sp. specimens) was subjected to molecular analysis, either to confirm our morphological identification or the MALDI-TOF MS results, as well as to identify the Culex species that were morphologically identified at the genus level and to resolve the discrepancies between the morphological identification and the MALDI-TOF MS identification.

RESULTS

High-quality MS spectra were obtained for 1058 of the 1253 specimens (84%), including 192/200 for Aedes, 589/662 for Anopheles and 277/391 for Culex. The blind test showed that 986/997 (99%) of the specimens were correctly identified by MALDI-TOF MS, with log score values ranging from 1.708 to 2.843. Eleven specimens of Culex could not be identified based on morphological features, MALDI-TOF MS or molecular analysis.

CONCLUSIONS

This study enabled us to identify several species of mosquitoes from Vietnam using MALDI-TOF MS, and to enrich our database of MALDI-TOF MS reference spectra.

Relative abundance and molecular identification of Culex pipiens complex (Diptera: Culicidae), in Kura Local Government Area, North-western Nigeria

Culex species are the most widespread mosquito species across the world and are known to be highly opportunistic, feeding on humans and livestock. They are known to acquire the potential to transmit zoonotic diseases, including Rift Valley Fever (RVF). However, despite their public health significance, they remain understudied in North-western Nigeria, compared to Anophelines. This study was therefore aimed at determining the relative abundance and Multiplex polymerase chain reaction (Multiplex PCR) identification of members of the Culex pipiens complex, in Kura Local Government Area (LGA), North-western, Nigeria. Adult mosquitoes were collected using Center for Disease Control (CDC) miniature light traps from August to October 2019. Mosquitoes were identified using morphological identification keys. Members of the Culex pipiens complex were further identified using Multiplex PCR to assess the presence of sibling species. A total of 413 mosquitoes, belonging to 3 genera, Culex, Anopheles and Aedes were collected. Of this figure, 120 Culex spp. females were collected. Homes with livestock had the highest occurrence of mosquitoes, 123 (61.19%) compared to those without livestock, 78 (38.81%). There was no statistical difference among the two (2) categories of homes (P ≥ 0.005). Culicoides spp. were the most common with 130 collected (65.38%). Again, homes with livestock had the highest occurrence, 85 whilst homes without livestock had 45 of the other flies caught. Multiplex- PCR revealed no expected bands for Cx. quinquefasciatus and Cx. pipiens from the DNA obtained from field collected mosquitoes as confirmed by using genomic DNA of an insectary Culex quinquefasciatus as control. Cx. spp. is presently regarded as a biting nuisance having no significant epidemiological importance. Efforts at its control should be intensified before it is too late. This study provides useful information on the occurrence and multiplex PCR of Culex spp in Kura Local Government Area, North-western Nigeria. These results have implications for the control of Culex spp. mosquito populations and the spread of human, livestock and avian diseases.

Tularemia as a Mosquito-Borne Disease

Francisella tularensis (Ft) is the etiological agent of tularemia, a disease known for over 100 years in the northern hemisphere. Ft includes four subspecies, of which two are the etiologic agents of tularemia: Ft subsp. tularensis (Ftt) and Ft subsp. holarctica (Fth), mainly distributed in North America and the whole northern hemisphere, respectively. Several routes of human infection with these bacteria exist, notably through bites of Ixodidae ticks. However, mosquitoes represent the main vectors of Fth in Scandinavia, where large tularemia outbreaks have occurred, usually during the warm season. The mechanisms making mosquitoes vectors of Fth are still unclear. This review covers the inventory of research work and epidemiological data linking tularemia to mosquitoes in Scandinavia and highlights the gaps in understanding mosquitoes and Ft interactions.

Genomic differentiation and intercontinental population structure of mosquito vectors Culex pipiens pipiens and Culex pipiens molestus

Understanding the population structure and mechanisms of taxa diversification is important for organisms responsible for the transmission of human diseases. Two vectors of West Nile virus, Culex pipiens pipiens and Cx. p. molestus, exhibit epidemiologically important behavioral and physiological differences, but the whole-genome divergence between them was unexplored. The goal of this study is to better understand the level of genomic differentiation and population structures of Cx. p. pipiens and Cx. p. molestus from different continents. We sequenced and compared the whole genomes of 40 individual mosquitoes from two locations in Eurasia and two in North America. Principal Component, ADMIXTURE, and neighbor joining analyses of the nuclear genomes identified two major intercontinental, monophyletic clusters of Cx. p. pipiens and Cx. p. molestus. The level of genomic differentiation between the subspecies was uniform along chromosomes. The ADMIXTURE analysis determined signatures of admixture in Cx. p. pipens populations but not in Cx. p. molestus populations. Comparison of mitochondrial genomes among the specimens showed a paraphyletic origin of the major haplogroups between the subspecies but a monophyletic structure between the continents. Thus, our study identified that Cx. p. molestus and Cx. p. pipiens represent different evolutionary units with monophyletic origin that have undergone incipient ecological speciation.

Microevolution of medically important mosquitoes - A review

This review intends to discuss central issues regarding the microevolution of mosquito (Culicidae) vectors of several pathogens and how this process impacts vector biology, disease transmission, and vector control attempts. On the microevolutionary context, it comparatively discusses the current knowledge on the population genetics of representatives of the genera Aedes, Anopheles and Culex, and comments on insecticide resistance of culicids. It also discusses other biological aspects of culicids that are not usually addressed in microevolutionary studies, such as vectorial competence, endosymbiosis, and wing morphology. One conclusion is that mosquitoes are highly genetically variable, adaptable, fast evolving, and have versatile vectorial competence. Unveiling microevolutionary patterns is fundamental for the design and maintenance of all control programs. Sampling methods for assessing microevolution must be standardized and must follow meaningful guidelines, such as those of "landscape genetics". A good understanding of microevolution requires more than a collection of case studies on population genetics and resistance. Future research could deal not only with the microevolution sensu stricto, but also with evolutionarily meaningful issues, such as inheritable characters, epigenetics, physiological cost-free plasticity, vector immunity, symbiosis, pathogen-mosquito co-evolution and environmental variables. A genotyping panel for seeking adaptive phenotypes as part of the standardization of population genetics methods is proposed. The investigative paradigm should not only be retrospective but also prospective, despite the unpredictability of evolution. If we integrate all suggestions to tackle mosquito evolution, a global revolution to counter vector-borne diseases can be provoked.

Effect of Serratia AS1 (Enterobacteriaceae: Enterobacteriales) on the Fitness of Culex pipiens (Diptera: Culicidae) for Paratransgenic and RNAi Approaches

The mosquito Culex pipiens is the primary vector of Rift Valley fever, West Nile, encephalitis, and Zika viruses, and periodic lymphatic filariasis. Developing insecticide resistance in mosquitoes demands the development of new approaches to fight these diseases. Paratransgenesis and RNAi approaches by using engineered bacteria have been shown to reduce mosquito vector competence. Serratia-AS1 is a bacterium found in mosquitoes and was genetically modified for expression of antimalaria effector molecules that repress development of malaria parasites in mosquitoes. The aim of this study was to determine how a genetically marked Serratia strain expressing the mCherry fluorescent protein (mCherry-Serratia) affects the colonization potential, life span, blood feeding behavior, fecundity, and fertility of Cx. pipiens. mCherry-Serratia bacteria disseminated into larvae, pupae, and newly emerged adults and dramatically increased in numbers following a blood meal. The bacterium was transmitted to progeny, showing that it can extend horizontally, transstadially, and vertically through the mosquito population. The presence of mCherry-Serratia did not affect blood feeding behavior, survival rate, fecundity, and fertility of Culex mosquitoes. This is the first study to evaluate the effects of an engineered bacteria on the fitness of Cx. pipiens. Although challenges remain, such as producing engineered bacteria to secrete anti-pathogens associated with Cx. pipiens, introducing such bacteria into mosquito populations, our findings of minimal fitness cost caused by Serratia-AS1 bode well for the development of paratransgenesis and RNAi approaches.

Wolbachia symbionts in mosquitoes: Intra- and intersupergroup recombinations, horizontal transmission and evolution

Many mosquitoes harbour Wolbachia symbionts that could affect the biology of their host in different ways. Evolutionary relationships of mosquitoes' Wolbachia infection, geographical distribution and symbiont prevalence in many mosquito species are not yet clear. Here, we present the results of Wolbachia screening of 17 mosquito species of four genera-Aedes, Anopheles, Coquillettidia and Culex collected from five regions of Eastern Europe and the Caucasus in 2012-2016. Based on multilocus sequence typing (MLST) data previously published and generated in this study, we try to reveal genetic links between mosquitoes' and other hosts' Wolbachia. The Wolbachia symbionts are found in Culex pipiens, Aedes albopictus and Coquillettidia richiardii and for the first time in Aedes cinereus and Aedes cantans, which are important vectors of human pathogens. Phylogenetic analysis demonstrated multiple origins of infection in mosquitoes although the one-allele-criterion approach revealed links among B-supergroup mosquito Wolbachia with allele content of lepidopteran hosts. The MLST gene content of strain wAlbA from the A-supergroup is linked with different ant species. Several cases of intersupergroup recombinations were found. One of them occurred in the wAlbaB strain of Aedes albopictus, which contains the coxA allele of the A-supergroup, whereas other loci, including wsp, belong to supergroup B. Other cases are revealed for non-mosquito symbionts and they exemplified genetic exchanges of A, B and F supergroups. We conclude that modern Wolbachia diversity in mosquitoes and in many other insect taxa is a recent product of strain recombination and symbiont transfers.

Dirofilaria and Wolbachia in mosquitoes (Diptera: Culicidae) in central European Russia and on the Black Sea coast

Dirofilariasis is endemic in Russia, as well as in many other European countries. The aim of this study was to assess the ability of mosquitoes to transfer Dirofilaria immitis and Dirofilaria repens in regions with temperate and subtropical climates. The possible impact of the symbiotic bacterium Wolbachia on Dirofilaria transmission was also investigated. 5333 female mosquitoes were collected at 11 points in central European Russia and on the Black Sea coast during the period 2013–2017. Out of 20 mosquito species examined, 14 were infected with D. repens and 13 with D. immitis. Both species of Dirofilaria were found in different climatic regions. The total Dirofilaria spp. estimated infection rate (EIR) in the central part of Russia varied from 3.1% to 3.7% and, in the southern region, from 1.1% to 3.0%. The highest estimated infection rate was found in Anopheles messeae, the lowest in Culex pipiens. The greatest epidemiological danger was represented by Aedes aegypti, Ae. geniculatus, An. messeae and Ae. communis. Six out of 20 mosquito species were infected with Wolbachia. Pools of Aedes albopictus, Cx. pipiens and Coquillettidia richiardii were simultaneously infected with Dirofilaria and Wolbachia. After checking mosquitoes individually, it was found that there was no development of Dirofilaria to the infective larval stage in specimens infected with Wolbachia. Twenty-two Dirofilaria-infective pools were Wolbachia-free and only two mosquito pools were Wolbachia-infected. The potential for transmission of Dirofilaria in mosquito species naturally uninfected with the symbiotic bacterium Wolbachia is higher than in species infected with the bacterium.

Accurate identification of Australian mosquitoes using protein profiling

Australian mosquito species significantly impact human health through nuisance biting and the transmission of endemic and exotic pathogens. Surveillance programmes designed to provide an early warning of mosquito-borne disease risk require reliable identification of mosquitoes. This study aimed to investigate the viability of Matrix-Assisted Laser Desorption/Ionization-Time-of-Flight Mass Spectrometry (MALDI-TOF MS) as a rapid and inexpensive approach to the identification of Australian mosquitoes and was validated using a three-step taxonomic approach. A total of 300 mosquitoes representing 21 species were collected from south-eastern New South Wales and morphologically identified. The legs from the mosquitoes were removed and subjected to MALDI-TOF MS analysis. Fifty-eight mosquitoes were sequenced at the cytochrome c oxidase subunit I (cox1) gene region and genetic relationships were analysed. We create the first MALDI-TOF MS spectra database of Australian mosquito species including 19 species. We clearly demonstrate the accuracy of MALDI-TOF MS for identification of Australian mosquitoes. It is especially useful for assessing gaps in the effectiveness of DNA barcoding by differentiating closely related taxa. Indeed, cox1 DNA barcoding was not able to differentiate members of the Culex pipiens group, Cx. quinquefasciatus and Cx. pipiens molestus, but these specimens were correctly identified using MALDI-TOF MS.

Evidence of natural Wolbachia infections and molecular identification of field populations of Culex pipiens complex (Diptera: Culicidae) mosquitoes in western Turkey

Establishing reliable risk projection information about the distribution pattern of members of the Culex pipiens complex is of particular interest, as these mosquitoes are competent vectors for certain disease-causing pathogens. Wolbachia, a maternally inherited bacterial symbiont, are distributed in various arthropod species and can induce cytoplasmic incompatibility, i.e., reduced egg hatch, in certain crosses. It is being considered as a tool for population control of mosquito disease vectors. The Aegean region is characterized by highly populated, rural, and agricultural areas and is also on the route of the migratory birds. In this study, a fragment of the 658 bp of the mitochondrial cytochrome c oxidase subunit 1 (COI) gene, which includes the barcode region, was employed to differentiate Cx. pipiens complex species found in this region. Moreover, for the first time, the prevalence of Wolbachia endobacteria in these natural populations was examined using PCR amplification of a specific wsp gene. Our results revealed a widespread (more than 90%, n=121) presence of the highly efficient West Nile virus vector Cx. quinquefasciatus in the region. We also found that Wolbachia infection is widespread; the average prevalence was 62% in populations throughout the region. This study provided valuable information about the composition of Cx. pipiens complex mosquitoes and the prevalence of Wolbachia infection in these populations in the Aegean region. This information will be helpful in tracking mosquito-borne diseases and designing and implementing Wolbachia-based control strategies in the region.

Wolbachia diversity and cytoplasmic incompatibility patterns in Culex pipiens populations in Turkey

Background

Wolbachia are maternally transmitted bacteria that can manipulate their hosts’ reproduction causing cytoplasmic incompatibility (CI). CI is a sperm-egg incompatibility resulting in embryonic death. Due to this sterilising effect on mosquitoes, Wolbachia are considered for vector control strategies. Important vectors for arboviruses, filarial nematodes and avian malaria, mosquitoes of Culex pipiens complex are suitable for Wolbachia-based vector control. They are infected with Wolbachia wPip strains belonging to five genetically distinct groups (wPip-I to V) within the Wolbachia B supergroup. CI properties of wPip strongly correlate with this genetic diversity: mosquitoes infected with wPip strains from a different wPip group are more likely to be incompatible with each other. Turkey is a critical spot for vector-borne diseases due to its unique geographical position as a natural bridge between Asia, Europe and Africa. However, general wPip diversity, distribution and CI patterns in natural Cx. pipiens (s.l.) populations in the region are unknown. In this study, we first identified wPip diversity in Turkish Cx. pipiens (s.l.) populations, by assigning them to one of the five groups within wPip (wPip-Ito V). We further investigated CI properties between different wPip strains from this region.

Results

We showed a wPip fixation in Cx. pipiens (s.l.) populations in Turkey by analysing 753 samples from 59 sampling sites. Three wPip groups were detected in the region: wPip-I, wPip-II and wPip-IV. The most dominant group was wPip-II. While wPip-IV was restricted to only two locations, wPip-I and wPip-II had wider distributions. Individuals infected with wPip-II were found co-existing with individuals infected with wPip-I or wPip-IV in some sampling sites. Two mosquito isofemale lines harbouring either a wPip-I or a wPip-II strain were established from a population in northwestern Turkey. Reciprocal crosses between these lines showed that they were fully compatible with each other but bidirectionally incompatible with wPip-IV Istanbul infected line.

Conclusion

Our findings reveal a high diversity of wPip and CI properties in Cx. pipiens (s.l.) populations in Turkey. Knowledge on naturally occurring CI patterns caused by wPip diversity in Turkey might be useful for Cx. pipiens (s.l.) control in the region.

The Role of Culex pipiens L. (Diptera: Culicidae) in Virus Transmission in Europe

Over the past three decades, a range of mosquito-borne viruses that threaten public and veterinary health have emerged or re-emerged in Europe. Mosquito surveillance activities have highlighted the Culex pipiens species complex as being critical for the maintenance of a number of these viruses. This species complex contains morphologically similar forms that exhibit variation in phenotypes that can influence the probability of virus transmission. Critical amongst these is the choice of host on which to feed, with different forms showing different feeding preferences. This influences the ability of the mosquito to vector viruses and facilitate transmission of viruses to humans and domestic animals. Biases towards blood-feeding on avian or mammalian hosts have been demonstrated for different Cx. pipiens ecoforms and emerging evidence of hybrid populations across Europe adds another level of complexity to virus transmission. A range of molecular methods based on DNA have been developed to enable discrimination between morphologically indistinguishable forms, although this remains an active area of research. This review provides a comprehensive overview of developments in the understanding of the ecology, behaviour and genetics of Cx. pipiens in Europe, and how this influences arbovirus transmission.

Sequence analysis of mtDNA COI barcode region revealed three haplotypes within Culex pipiens assemblage

Members of the Culex (Culex) pipiens assemblage are known vectors of deadly encephalitides, periodic filariasis, and West Nile virus throughout the world. However, members of this assemblage are morphologically indistinguishable or hard to distinguish and play distinct roles in transmission of the diseases. The current study aimed to provide further evidence on utility of the two most popular nuclear (ITS2-rDNA) and mitochondrial (COI barcode region) genetic markers to identify members of the assemblage. Culex pipiens assemblage specimens from different climate zones of Iran were collected and identified to species level based on morphological characteristics. Nucleotide sequences of the loci for the specimens plus available data in the GenBank were analyzed to find species specific genetic structures useful for diagnosis purposes. ITS2 region was highly divergent within species or populations suggesting lack of consistency as a reliable molecular marker. In contrast, sequence analysis of 710 bp of COI gene revealed three fixed haplotypes named here "C, T, H" within the assemblage which can be distinguished by HaeIII and AluI enzymes. There were a correlation between the haplotypes and the world climate regions, where the haplotypes H/T and C are present mainly in temperate and tropical regions of the world, respectively. In the New world, Australia, and Japan only haplotype H is found. In conjunction between tropical and temperate regions such Iran, China, and Turkey, a mix of C/H or C/H/T are present. Although, the haplotypes are not strictly species-specific, however, Cx. quinquefasciatus was mainly of haplotype C. Due to the lack of mating barrier and questionable taxonomic situation of the complex members, the mentioned haplotypes in combination with other morphological and molecular characters might be used to address the genetic structure of the studied populations.

Ecophysiological characterization and molecular differentiation of Culex pipiens forms (Diptera: Culicidae) in Tunisia

Background

The Culex pipiens complex (Diptera: Culicidae) includes the most widespread mosquito species in the world. Members of this complex are the primary enzootic and epidemic vectors of the West Nile virus (genus Flavivirus) in several countries. The two recognized forms of Cx. pipiens (Linnaeus, 1758) - pipiens and molestus- exhibit behavioral and physiological differences. Natural populations of Cx. pipiens were investigated in several sites in Tunisia to evaluate the ecophysiological and molecular characteristics of their forms.

Results

The analysis showed the sympatric presence of Cx. pipiens forms and hybrids in all studied sites. Of all the tested larvae of Cx. pipiens, 33.5% were identified as pipiens, 30.8% were identified as molestus, and 35.6% were identified as hybrids. The molestus and hybrid forms were positively correlated with urban habitats and belowground sites while the pipiens form was positively correlated with rural habitats and aboveground sites. Autogeny was expressed in all types of habitats and breeding sites. By contrast with the microsatellite CQ11, the two molecular markers, ace-2 and cytb, did not allow differentiation between the Cx. pipiens forms.

Conclusions

Our study shows the ubiquitous distribution and the plasticity of the different forms of Cx. pipiens in a wide range of ecological conditions. It suggests that the behavioral traits assigned to the forms of Cx. pipiens seem to be more flexible than previously assumed. Our analysis also proves that the microsatellite CQ11 remains an efficient tool for distinguishing between Cx. pipiens forms.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2265-7) contains supplementary material, which is available to authorized users.

The mosquito fauna of the western region of Spain with emphasis on ecological factors and the characterization of Culex pipiens forms

This study updates the diversity, distribution, and seasonal trends of mosquitoes in a western region of Spain, assesses ecological determinants of Culex pipiens s.l., and determines form composition of Cx. pipiens s.s.

POPULATIONS

A total of 1,495 mosquitoes of 16 species was collected during 2012-2013, of which Cx. pipiens s.l. and Cx. theileri were the most abundant. Five new records for An. maculipennis s.s., Orthopodomyia pulcripalpis, Aedes (Ochlerotatus) punctor, Cx. europaeus, and Cx. modestus were found for this region. Cx. pipiens density varied across weather and habitat patterns, correlating positively with high temperatures and with a preference for urbanized areas and rural areas within a proximity of ovine farms. Moreover, molecular identification by CQ11FL was performed in 467 Cx. pipiens s.s., detecting both pipiens (66%) and molestus (8.4%) forms coexisting in different habitats (urban, peri-urban and rural) aboveground with a high degree of hybridization (25.7%). The abundance of Cx. pipiens in urban areas and farms, with the presence of hybrids, may increase their capacity to act as bridge vectors for the transmission of arboviral infections. These data will be helpful for further implementation of entomological programs focused on risk assessment for arboviruses or other mosquito-borne pathogens.

Molecular detection of Wolbachia pipientis in natural populations of mosquito vectors of Dirofilaria immitis from continental Portugal: first detection in Culex theileri

Wolbachia pipientis (Rickettsiales: Rickettsiaceae) protects mosquitoes from infections with arboviruses and parasites. However, the effect of its co-infection on vector competence for Dirofilaria immitis (Spirurida: Onchocercidae) in the wild has not been investigated. This study aimed to screen vectors of D. immitis for wPip, to characterize these, and to investigate a possible association between the occurrence of W. pipientis and that of the nematode. The presence of W. pipientis was assessed in the five mosquito potential vectors of D. immitis in Portugal. Polymerase chain reaction (PCR) products were sequenced, and wPip haplotypes were determined by PCR-restricted fragment length polymorphism (RFLP). Results showed that wPip was detected in 61.5% of Culex pipiens (Diptera: Culicidae) pools and 6.3% of Culex theileri pools. wPip 16s rRNA sequences found in Cx. theileri exactly match those from Cx. pipiens, confirming a mosquito origin, rather than a nematode origin, as some specimens were infected with D. immitis. Only wPip haplotype I was found. No association was found between the presence of wPip and D. immitis in mosquitoes and hence a role for this endosymbiont in influencing vectorial competence is yet to be identified. This study contributes to understanding of wPip distribution in mosquito populations and, to the best of the authors' knowledge, is the first report of natural infections by wPip in Cx. theileri.