Occurrence and host preferences of Anopheles maculipennis group mosquitoes in England and Wales

Mayaro virus, a potential threat for Europe: vector competence of autochthonous vector species

BACKGROUND

Mayaro virus (MAYV) is an emerging alphavirus, primarily transmitted by the mosquito Haemagogus janthinomys in Central and South America. However, recent studies have shown that Aedes aegypti, Aedes albopictus and various Anopheles mosquitoes can also transmit the virus under laboratory conditions. MAYV causes sporadic outbreaks across the South American region, particularly in areas near forests. Recently, cases have been reported in European and North American travelers returning from endemic areas, raising concerns about potential introductions into new regions. This study aims to assess the vector competence of three potential vectors for MAYV present in Europe.

METHODS

Aedes albopictus from Italy, Anopheles atroparvus from Spain and Culex pipiens biotype molestus from Belgium were exposed to MAYV and maintained under controlled environmental conditions. Saliva was collected through a salivation assay at 7 and 14 days post-infection (dpi), followed by vector dissection. Viral titers were determined using focus forming assays, and infection rates, dissemination rates, and transmission efficiency were calculated.

RESULTS

Results indicate that Ae. albopictus and An. atroparvus from Italy and Spain, respectively, are competent vectors for MAYV, with transmission possible starting from 7 dpi under laboratory conditions. In contrast, Cx. pipiens bioform molestus was unable to support MAYV infection, indicating its inability to contribute to the transmission cycle.

CONCLUSIONS

In the event of accidental MAYV introduction in European territories, autochthonous outbreaks could potentially be sustained by two European species: Ae. albopictus and An. atroparvus. Entomological surveillance should also consider certain Anopheles species when monitoring MAYV transmission.

Patterns of genetic differentiation imply distinct phylogeographic history of the mosquito species Anopheles messeae and Anopheles daciae in Eurasia

Detailed knowledge of phylogeography is important for control of mosquito species involved in the transmission of human infectious diseases. Anopheles messeae is a geographically widespread and genetically diverse dominant vector of malaria in Eurasia. A closely related species, An. daciae, was originally distinguished from An. messeae based on five nucleotide substitutions in its ribosomal DNA (rDNA). However, the patterns of phylogeographic history of these species in Eurasia remain poorly understood. Here, using internal transcribed spacer 2 (ITS2) of rDNA and karyotyping for the species identification we determined the composition of five Anopheles species in 28 locations in Eurasia. Based on the frequencies of 11 polymorphic chromosomal inversions used as genetic markers, a large-scale population genetics analysis was performed of 1932 mosquitoes identified as An. messeae, An. daciae and their hybrids. The largest genetic differences between the species were detected in the X sex chromosome suggesting a potential involvement of this chromosome in speciation. The frequencies of autosomal inversions in the same locations differed by 13%-45% between the species demonstrating a restricted gene flow between the species. Overall, An. messeae was identified as a diverse species with a more complex population structure than An. daciae. The clinal gradients in frequencies of chromosomal inversions were determined in both species implicating their possible involvement in climate adaptations. The frequencies of hybrids were low ~1% in northern Europe but high up to 50% in south-eastern populations. Thus, our study revealed critical differences in patterns of phylogeographic history between An. messeae and An. daciae in Eurasia. This knowledge will help to predict the potential of the malaria transmission in the northern territories of the continent.

Updated occurrence and bionomics of potential malaria vectors in Europe: a systematic review (2000-2021)

Despite the eradication of malaria across most European countries in the 1960s and 1970s, the anopheline vectors are still present. Most of the malaria cases that have been reported in Europe up to the present time have been infections acquired in endemic areas by travelers. However, the possibility of acquiring malaria by locally infected mosquitoes has been poorly investigated in Europe, despite autochthonous malaria cases having been occasionally reported in several European countries. Here we present an update on the occurrence of potential malaria vector species in Europe. Adopting a systematic review approach, we selected 288 papers published between 2000 and 2021 for inclusion in the review based on retrieval of accurate information on the following Anopheles species: An. atroparvus, An. hyrcanus sensu lato (s.l.), An. labranchiae, An. maculipennis sensu stricto (s.s.), An. messeae/daciae, An. sacharovi, An. superpictus and An. plumbeus. The distribution of these potential vector species across Europe is critically reviewed in relation to areas of major presence and principal bionomic features, including vector competence to Plasmodium. Additional information, such as geographical details, sampling approaches and species identification methods, are also reported. We compare the information on each species extracted from the most recent studies to comparable information reported from studies published in the early 2000s, with particular reference to the role of each species in malaria transmission before eradication. The picture that emerges from this review is that potential vector species are still widespread in Europe, with the largest diversity in the Mediterranean area, Italy in particular. Despite information on their vectorial capacity being fragmentary, the information retrieved suggests a re-definition of the relative importance of potential vector species, indicating An. hyrcanus s.l., An. labranchiae, An. plumbeus and An. sacharovi as potential vectors of higher importance, while An. messeae/daciae and An. maculipennis s.s. can be considered to be moderately important species. In contrast, An. atroparvus and An. superpictus should be considered as vectors of lower importance, particularly in relation to their low anthropophily. The presence of gaps in current knowledge of vectorial systems in Europe becomes evident in this review, not only in terms of vector competence but also in the definition of sampling approaches, highlighting the need for further research to adopt the appropriate surveillance system for each species.

New Cytogenetic Photomap and Molecular Diagnostics for the Cryptic Species of the Malaria Mosquitoes Anopheles messeae and Anopheles daciae from Eurasia

The Eurasian malaria vector Anopheles messeae is a widely spread and genetically diverse species. Five widespread polymorphic chromosomal inversions were found in natural populations of this mosquito. A cryptic species, Anopheles daciae, was differentiated from An. messeae by the presence of several nucleotide substitutions in the Internal Transcribed Spacer 2 (ITS2) region of ribosomal DNA. However, because of the absence of a high-quality reference cytogenetic map, the inversion polymorphisms in An. daciae and An. messeae remain poorly understood. Moreover, a recently determined heterogeneity in ITS2 in An. daciae questioned the accuracy of the previously used Restriction Fragment Length Polymorphism (RFLP) assay for species diagnostics. In this study, a standard-universal cytogenetic map was constructed based on orcein stained images of chromosomes from salivary glands for population studies of the chromosomal inversions that can be used for both An. messeae and An. daciae. In addition, a new ITS2-RFLP approach for species diagnostics was developed. Both methods were applied to characterize inversion polymorphism in populations of An. messeae and An. daciae from a single location in Western Siberia in Russia. The analysis demonstrates that cryptic species are remarkably different in their frequencies of chromosomal inversion variants. Our study supports previous observations that An. messeae has higher inversion polymorphism in all autosomes than the cryptic species An. daciae.

DNA identification of species of the Anopheles maculipennis complex and first record of An. daciae in Belgium

The present study aimed at identifying the members of the Anopheles maculipennis complex (Diptera: Culicidae) occurring in Belgium. Therefore, the second internal transcribed spacer of nuclear ribosomal DNA (ITS2) and the mitochondrial cytochrome oxidase subunit I (COI) loci were sequenced in 175 and 111 specimens, respectively, collected between 2007 and 2019. In parallel, the suitability of two species-diagnostic PCR-RFLP assays was tested. The identified specimens included: An. maculipennis s.s. (N = 105), An. daciae (N = 62), An. atroparvus (N = 6) and An. messeae (N = 2). Each species was characterized by unique ITS2 haplotypes, whereas COI only supported the monophyly of An. atroparvus, a historical malaria vector in Belgium. Species identification results were further supported by unique PCR-RFLP banding patterns. We report for the first time An. daciae in Belgium, where it was found to co-occur with An. maculipennis s.s. The latter was the most prevalent in the collection studied (60%) and appears to have the widest distribution in Belgium. As in other studies, An. daciae and An. messeae appeared the most closely related species, up to the point that their species status remains debatable, while their ecological differences, including vector competences, need further study.

Blood-feeding ecology of mosquitoes in two zoological gardens in the United Kingdom

BACKGROUND

Zoological gardens contain unique configurations of exotic and endemic animals and plants that create a diverse range of developing sites and potential sources of blood meals for local mosquitoes. This may imply unusual interspecific pathogen transmission risks involving zoo vertebrates, like avian malaria to captive penguins. Understanding mosquito ecology and host feeding patterns is necessary to improve mosquito control and disease prevention measures in these environments.

METHODS

Mosquito sampling took place in Chester Zoo for 3 years (2017, 2018, and 2019) and for 1 year in Flamingo Land (2017) using different trapping methods. Blood-fed mosquitoes were identified and their blood meal was amplified by PCR, sequenced, and blasted for host species identification.

RESULTS

In total, 640 blood-fed mosquitoes were collected [Culex pipiens (n = 497), Culiseta annulata (n = 81), Anopheles maculipennis s.l. (n = 7), An. claviger (n = 1), and unidentifiable (n = 55)]. Successful identification of the host species was achieved from 159 blood-fed mosquitoes. Mosquitoes fed on birds (n = 74), non-human mammals (n = 20), and humans (n = 71). There were mixed blood meals from two hosts (n = 6). The proportions of blood-fed mosquitoes varied across sampling seasons and sites within the zoos. The use of resting traps and aspiration of vegetation were more efficient techniques for capturing blood-fed mosquitoes than traps for host-seeking or gravid mosquitoes. By relating the locations of zoo vertebrates to where fed mosquitoes were trapped, the minimum travelling distances were calculated (13.7 to 366.7 m). Temperature, precipitation, relative humidity, proximity to zoo vertebrate exhibits, and vegetation level were found to be significantly associated with the proportion of captured blood-fed mosquitoes by generalized linear modelling.

CONCLUSIONS

Mosquito feeding behaviour in zoos is mainly influenced by time, location (sampling area), temperature, and host availability, which highlights the value of mosquito monitoring in complex settings to plan control strategies and potentially reduce inherent disease transmission risks for humans and threatened zoo vertebrates.

Analysis of Anopheles messeae s.l. intron gene polymorphism associated with imidacloprid resistance

Due to their high solubility and stability, neonicotinoid insecticides are able to accumulate in water bodies, affecting aquatic organisms. The aims of this study were to evaluate resistance (LC₅₀ ) of Anopheles messeae s.l. (Anopheles messeae and An. daciae) to the neonicotinoid imidacloprid and to search for genetic markers associated with insecticide resistance. The LC₅₀ values of these species in the collections during 2017 and 2018 were indistinguishable and were in the range of 0.027-0.051 mg/l. In general, the LC₅₀ values of the mosquitoes were comparable with values of other mosquito species of the Anopheles and Culex genera. Gene polymorphisms of the variations in intron lengths and the presence of restriction sites in introns that were potentially associated with the metabolism of insecticides were studied. Polymorphisms of the studied genes in the pair of closely related species considered overlapped, but allele frequencies were different. Part of the genetic variants arose due to insertions of repetitive elements of the genome. Two variants of the cytochrome P450 gene Cyp6AG1 in An. daciae were associated with increased resistance to imidacloprid. Possible side effects of selection on insecticide resistance in blood-sucking mosquitoes are discussed.

Single nucleotide polymorphism analysis of the ITS2 region of two sympatric malaria mosquito species in Sweden: Anopheles daciae and Anopheles messeae

Four species of the Anopheles maculipennis complex have previously been recorded in Sweden. A recent addition to the complex is Anopheles daciae, which is considered to be closely related to, but distinct from Anopheles messeae. The original designation of An. daciae was based on five genetic differences (161, 165, 167, 362 and 382) in the second internal transcribed spacer (ITS) 2 of the ribosomal RNA. Further studies have shown that only two nucleotide differences (362 and 382) robustly separate the species. Thirty-three An. maculipennis complex mosquitoes were collected in the province of Uppland, Sweden. All were An. daciae but showed double peaks for three variable positions (161, 165 and 167). When cloned, the intra-individual nucleotide variation was almost exclusively fixed with either TTC or AAT, originally diagnostic for An. messae and An. daciae, respectively. To further investigate the intra-individual variation, nine An. daciae and 11 An. messeae were collected in southern Sweden and their ITS2 fragments were amplified and sequenced using Illumina MiSeq sequencing (Illumina, Inc., San Diego, CA, USA). For the diagnostic nucleotide 382 no intra-individual variation could be detected. However, although each An. daciae specimen carried several ITS2 sequence variants for the four other nucleotides, there was no intra-individual variation in the An. messeae specimens.

Anopheles daciae, a new country record for Finland

Mosquitoes (Diptera: Culicidae) were collected throughout Finland between 2013 and 2018 to determine species distributions. During the course of molecular identifications of specimens belonging to the Anopheles maculipennis complex, ribosomal internal transcribed spacer 2 sequences and link-reared specimens revealed the presence of Anopheles daciae Linton, Nicolescu & Harbach (n = 37), a new country record, as well as Anopheles messeae Falleroni (n = 19) in the collections. Although the sample size is low, distinctions are apparent in the distributions of these two species, with An. daciae present in south-eastern and central Finland, including the regions of Kanta-Häme, Pirkanmaa, Pohjois-Pohjanmaa, Päijät-Häme and Satakunta, and An. messeae present in the southern and south-eastern regions of Åland (Ahvenanmaa), Etelä-Savo, Kanta-Häme, Kymenlaakso, Päijät-Häme, Satakunta, Uusimaa and Varsinais-Suomi. All reports of An. messeae in Finland prior to 2018 should therefore be recognized as potentially being either An. messeae or An. daciae. Because these species are potential vectors of malarial protozoa, it is important to have full knowledge of their distributions across Europe, particularly in the face of climate warming.

Chromosome and Genome Divergence between the Cryptic Eurasian Malaria Vector-Species Anopheles messeae and Anopheles daciae

Chromosomal inversions are important drivers of genome evolution. The Eurasian malaria vector Anophelesmesseae has five polymorphic inversions. A cryptic species, An. daciae, has been discriminated from An. messeae based on five fixed nucleotide substitutions in the internal transcribed spacer 2 (ITS2) of ribosomal DNA. However, the inversion polymorphism in An. daciae and the genome divergence between these species remain unexplored. In this study, we sequenced the ITS2 region and analyzed the inversion frequencies of 289 Anopheles larvae specimens collected from three locations in the Moscow region. Five individual genomes for each of the two species were sequenced. We determined that An. messeae and An. daciae differ from each other by the frequency of polymorphic inversions. Inversion X1 was fixed in An. messeae but polymorphic in An. daciae populations. The genome sequence comparison demonstrated genome-wide divergence between the species, especially pronounced on the inversion-rich X chromosome (mean Fst = 0.331). The frequency of polymorphic autosomal inversions was higher in An. messeae than in An. daciae. We conclude that the X chromosome inversions play an important role in the genomic differentiation between the species. Our study determined that An. messeae and An. daciae are closely related species with incomplete reproductive isolation.

Emerging Threats to Animals in the United Kingdom by Arthropod-Borne Diseases

Worldwide, arthropod-borne disease transmission represents one of the greatest threats to public and animal health. For the British Isles, an island group on the north-western coast of continental Europe consisting of the United Kingdom (UK) and the Republic of Ireland, physical separation offers a barrier to the introduction of many of the pathogens that affect animals on the rest of the continent. Added to this are strict biosecurity rules at ports of entry and the depauperate vector biodiversity found on the islands. Nevertheless, there are some indigenous arthropod-borne pathogens that cause sporadic outbreaks, such as the tick-borne louping ill virus, found almost exclusively in the British Isles, and a range of piroplasmid infections that are poorly characterized. These provide an ongoing source of infection whose emergence can be unpredictable. In addition, the risk remains for future introductions of both exotic vectors and the pathogens they harbor, and can transmit. Current factors that are driving the increases of both disease transmission and the risk of emergence include marked changes to the climate in the British Isles that have increased summer and winter temperatures, and extended the period over which arthropods are active. There have also been dramatic increases in the distribution of mosquito-borne diseases, such as West Nile and Usutu viruses in mainland Europe that are making the introduction of these pathogens through bird migration increasingly feasible. In addition, the establishment of midge-borne bluetongue virus in the near continent has increased the risk of wind-borne introduction of infected midges and the inadvertent importation of infected cattle. Arguably the greatest risk is associated with the continual increase in the movement of people, pets and trade into the UK. This, in particular, is driving the introduction of invasive arthropod species that either bring disease-causing pathogens, or are known competent vectors, that increase the risk of disease transmission if introduced. The following review documents the current pathogen threats to animals transmitted by mosquitoes, ticks and midges. This includes both indigenous and exotic pathogens to the UK. In the case of exotic pathogens, the pathway and risk of introduction are also discussed.

Species composition, geographical distribution and seasonal abundance of the Anopheles maculipennis complex along the Upper Rhine, Germany

Between May and September 2016, mosquitoes were collected on a biweekly basis at 55 locations with CO₂-baited encephalitis vector surveillance traps along the Upper Rhine, Germany, to evaluate the species composition, geographical distribution and abundance of the Anopheles maculipennis complex, some members of this complex being considered vectors of historical malaria in Germany. A total of 2115 Anopheles maculipennis complex specimens were collected during the season, of which a sample of 1252 individuals was determined to species level by amplification of species-specific internal transcribed spacer 2 (ITS2) sequences. A total of 856 individuals of Anopheles daciae (68.37%), 394 Anopheles messeae (31.47%) and 2 Anopheles maculipennis s.s. (0.16%) were recorded. The number and proportion of A. daciae was remarkably higher in the northern meandering zone of the Upper Rhine (843 specimens, 79.90%), than in the more canalised southern furcation zone where A. messeae with 183 collected specimens represented 92.89% of 197 classified individuals. The average number of collected A. maculipennis s.l. individuals per trapping site was 38.45, equalling 0.64% of the total mosquito collection. Despite an increase in imported malaria cases, this comparatively low abundance of A. maculipennis s.l. may indicate a low risk of endemic malaria transmission by members of the A. maculipennis complex today. The proportionally dominance of A. daciae suggests that this species could be suspected the main historical vector of malaria in the Upper Rhine region. Sequence analyses of the ITS2 fragment revealed intraindividual polymorphisms within 3 of 5 diagnostic nucleotides in all specimens of A. daciae, raising the question if additional loci should be considered, to gain further insight into the taxonomical relation to A. messeae.

Identification of novel Glutathione S-Transferases epsilon 2 mutation in Anopheles maculipennis s.s. (Diptera: Culicidae)

Anopheles maculipennis complex comprises some important malaria vectors in Iran, Middle East, and Europ. The principal way to control of malaria remains on the use of chemical insecticides against its vectors because there is no vaccine for malaria prevention. Extensive use of organophosphate compounds has caused to emergence and distribution of insecticide resistance in Anopheles species in Asia. The current study aimed to the detection of three well-known amino acid substitutions (I114T, L119F, and F120L) in the Glutathione S-Transferases epsilon 2 (GSTe2) gene are associated with DDT and organophosphate insecticides resistance in an Anopheles maculipennis population collected from Iran. Adult samples of An. maculipennis were collected by hand and Total catch in Animal and Human Shelters from Azerbaijan-Gharbi and Zanjan provinces. Following morphological identification, DNA was extracted by YTA Genomic DNA Extraction Mini Kit for amplification of rDNA-ITS2 and GSTe2 fragments. ∼500 bp fragment was amplified using F rDNA-ITS2 and GSTe2 primers. rDNA-ITS2 sequence analysis showed 100% similarity with An. maculipennis. GSTe2 nucleotide sequence similarity within species was 99-100%, while, it was 95-96 % when compared with Anopheles sacharovi GSTe2 sequences available in GenBank. Amino acid sequence comparisons showed a novel amino acid substitution in N148D position with 15.79% frequency. The current study reports new GSTe2 amino acid substitution in An. maculipennis s.s., for the first time. The function of the mutation N148D and its association with resistance phenotype need to validate. However, the integration of these data into the malaria control program still remains a challenge.

Estimated resistance of the malaria mosquito Anopheles messeae s.l. to the insecticide malathion

Resistance to agricultural pesticides is an important and insufficiently studied concern for pest and disease vector research. We determined the malathion resistance of species in the Anopheles maculipennis mosquito group in a habitat near Novosibirsk, Russia. Most of the 851 individuals we measured were members of the Anopheles messeae s.l. complex (An. messeae and An. daciae species). The LC₅₀ value for malathion was 0.052 mg/L for the mixed specimens, and we failed to find any differences between species. The LC₅₀ value was within the range of values for malathion resistance of Anopheles stephensi and Culex quinquefasciatus. As the main resistance mechanism to organophosphate and carbamate insecticides is a single mononucleotide substitution in the ace-1 gene, we searched for this mutation in An. messeae s.l. and An. beklemishevi by restriction analysis. This mutation was not found in 347 of the specimens. We sequenced the ace-1 gene fragment for 24 specimens from four species of the Anopheles maculipennis group, including An. messeae, An. daciae, An. atroparvus, and An. beklemishevi. These specimens harbored a nucleotide substitution in the triplet where a mutation can lead to insecticide resistance, but this substitution would make it difficult for the resistance to develop. Since the studied specimens belong to branches of the Palearctic portion of the Anopheles maculipennis group, we suspect that all other Palearctic species of this group would have difficulties harboring the ace-1 mutation that would lead to organophosphate and carbamate resistance.

Mosquito bloodmeal preferences in two zoological gardens in Germany

Because they provide a high density and diversity of vertebrate species, small water pools and shaded environments, zoological gardens offer ideal living conditions for numerous mosquito species. Depending on their host preferences and vector competencies, these species may be able to transmit pathogens between native and non-adapted exotic blood host species, thereby causing morbidity and mortality among valuable zoo animals. To determine the extent to which native mosquito species feed on captive and wild animals, as well as on humans, in two German zoological gardens, mosquitoes were collected over two seasons by trapping and aspirating. A total of 405 blood-fed specimens belonging to 16 mosquito taxa were collected. Genetic bloodmeal analysis revealed 56 host species, mainly representing mammals of the zoo animal population, including exotic species previously not known as blood hosts of the mosquito species collected. These results indicate opportunistic feeding patterns with low host-specificity in the analysed mosquitoes, although these could be grouped, according to their bloodmeals, into 'amphibian-', 'non-human mammal-' and 'non-human mammal and human-' feeding species. As the blood-feeding preferences of vector-competent mosquito species are major determinants of vector capacity, information on the blood-feeding behaviour of mosquitoes in zoos is crucial to the success of targeted vector management.

DNA barcoding of British mosquitoes (Diptera, Culicidae) to support species identification, discovery of cryptic genetic diversity and monitoring invasive species

Correct mosquito species identification is essential for mosquito and disease control programs. However, this is complicated by the difficulties in morphologically identifying some mosquito species. In this study, variation of a partial sequence of the cytochrome c oxidase unit I (COI) gene was used for the molecular identification of British mosquito species and to facilitate the discovery of cryptic diversity, and monitoring invasive species. Three DNA extraction methods were compared to obtain DNA barcodes from adult specimens. In total, we analyzed 42 species belonging to the genera Aedes Meigen, 1818 (21 species), Anopheles Meigen, 1818 (7 species), Coquillettidia Theobald, 1904 (1 species), Culex Linnaeus, 1758 (6 species), Culiseta Felt, 1904 (7 species), and Orthopodomyia Theobald, 1904 (1 species). Intraspecific genetic divergence ranged from 0% to 5.4%, while higher interspecific divergences were identified between Aedesgeminus Peus, 1971/Culisetalitorea (Shute, 1928) (24.6%) and Ae.geminus/An.plumbeus Stephens, 1828 (22.5%). Taxonomic discrepancy was shown between An.daciae Linton, Nicolescu & Harbach, 2004 and An.messeae Falleroni, 1828 indicating the poor resolution of the COI DNA barcoding region in separating these taxa. Other species such as Ae.cantans (Meigen, 1818)/Ae.annulipes (Meigen, 1830) showed similar discrepancies indicating some limitation of this genetic marker to identify certain mosquito species. The combination of morphology and DNA barcoding is an effective approach for the identification of British mosquitoes, for invasive mosquitoes posing a threat to the UK, and for the detection of hidden diversity within species groups.

Distribution of Anopheles daciae and other Anopheles maculipennis complex species in Serbia

Malaria is one of the most severe health problems facing the world today. Until the mid-twentieth century, Europe was an endemic area of malaria, with the Balkan countries being heavily infested. Sibling species belonging to the Anopheles maculipennis complex are well-known as effective vectors of Plasmodium in Europe. A vast number of human malaria cases in the past in the former Yugoslavia territory have stressed the significance of An. maculipennis complex species as primary and secondary vectors. Therefore, the present study evaluates the species composition, geographic distribution and abundance of these malaria vector species. Mosquitoes were collected in the northern Serbian province of Vojvodina and analysed by PCR-RFLP, multiplex PCR and sequencing of the ITS2 intron of genomic rDNA. Four sibling species of the An. maculipennis complex were identified. Both larvae and adults of the recently described species An. daciae were identified for the first time in Serbia. In 250 larval samples, 109 (44%) An. messeae, 90 (36%) An. maculipennis s.s., 33 (13%) An. daciae and 18 (7%) An. atroparvus were identified. In adult collections, 81 (47%) An. messeae, 55 (32%) An. daciae, 33 (19%) An. maculipennis s.s., and 3 (2%) An. atroparvus were recorded. The most abundant species in Vojvodina was An. messeae, whereas An. atroparvus was confirmed a rare species in all parts. Since this species is a potentially, highly competent malarial vector, low population density could be crucial to prevent a new establishment of endemic malaria transmission in Serbia.

Mosquito species composition and phenology (Diptera, Culicidae) in two German zoological gardens imply different risks of mosquito-borne pathogen transmission

Due to their large diversity of potential blood hosts, breeding habitats, and resting sites, zoological gardens represent highly interesting places to study mosquito ecology. In order to better assess the risk of mosquito-borne disease-agent transmission in zoos, potential vector species must be known, as well as the communities in which they occur. For this reason, species composition and dynamics were examined in 2016 in two zoological gardens in Germany. Using different methods for mosquito sampling, a total of 2,257 specimens belonging to 20 taxa were collected. Species spectra depended on the collection method but generally differed between the two zoos, while species compositions and relative abundances varied seasonally in both of them. As both sampled zoos were located in the same climatic region and potential breeding sites within the zoos were similar, the differences in mosquito compositions are attributed to immigration of specimens from surrounding landscapes, although the different sizes of the zoos and the different blood host populations available probably also have an impact. Based on the differences in species composition and the various biological characteristics of the species, the risk of certain pathogens to be transmitted must also be expected to differ between the zoos.

Partial-arm translocations in evolution of malaria mosquitoes revealed by high-coverage physical mapping of the Anopheles atroparvus genome

Background

Malaria mosquitoes have had a remarkable stability in the number of chromosomes in their karyotype (2n = 6) during 100 million years of evolution. Moreover, autosomal arms were assumed to maintain their integrity even if their associations with each other changed via whole-arm translocations. Here we use high-coverage comparative physical genome mapping of three Anopheles species to test the extent of evolutionary conservation of chromosomal arms in malaria mosquitoes.

Results

In this study, we developed a physical genome map for Anopheles atroparvus, one of the dominant malaria vectors in Europe. Using fluorescence in situ hybridization (FISH) of DNA probes with the ovarian nurse cell polytene chromosomes and synteny comparison, we anchored 56 genomic scaffolds to the An. atroparvus chromosomes. The obtained physical map represents 89.6% of the An. atroparvus genome. This genome has the second highest mapping coverage among Anophelinae assemblies after An. albimanus, which has 98.2% of the genome assigned to its chromosomes. A comparison of the An. atroparvus, An. albimanus, and An. gambiae genomes identified partial-arm translocations between the autosomal arms that break down the integrity of chromosome elements in evolution affecting the structure of the genetic material in the pericentromeric regions. Unlike An. atroparvus and An. albimanus, all chromosome elements of An. gambiae are fully syntenic with chromosome elements of the putative ancestral Anopheles karyotype. We also detected nonrandom distribution of large conserved synteny blocks and confirmed a higher rate of inversion fixation in the X chromosome compared with autosomes.

Conclusions

Our study demonstrates the power of physical mapping for understanding the genome evolution in malaria mosquitoes. The results indicate that syntenic relationships among chromosome elements of Anopheles species have not been fully preserved because of multiple partial-arm translocations.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4663-4) contains supplementary material, which is available to authorized users.

Olfaction, experience and neural mechanisms underlying mosquito host preference

Mosquitoes are best known for their proclivity towards biting humans and transmitting bloodborne pathogens, but there are over 3500 species, including both blood-feeding and non-blood-feeding taxa. The diversity of host preference in mosquitoes is exemplified by the feeding habits of mosquitoes in the genus Malaya that feed on ant regurgitation or those from the genus Uranotaenia that favor amphibian hosts. Host preference is also by no means static, but is characterized by behavioral plasticity that allows mosquitoes to switch hosts when their preferred host is unavailable and by learning host cues associated with positive or negative experiences. Here we review the diverse range of host-preference behaviors across the family Culicidae, which includes all mosquitoes, and how adaptations in neural circuitry might affect changes in preference both within the life history of a mosquito and across evolutionary time-scales.

Cryptic species Anopheles daciae (Diptera: Culicidae) found in the Czech Republic and Slovakia

We report the distribution of mosquitoes of the maculipennis complex in two distinct areas of the Czech Republic (Bohemia and South Moravia) and in one locality of neighbouring Slovakia with emphasis on the detection of the newly described cryptic species Anopheles daciae (Linton, Nicolescu & Harbach, 2004). A total of 691 mosquitoes were analysed using a species-specific multiplex PCR assay to differentiate between the members of the maculipennis complex. In the Czech Republic, we found Anopheles maculipennis (with a prevalence rate of 1.4%), Anopheles messeae (49.0%) and Anopheles daciae (49.6%). In Slovakia, only An. messeae (52.1%) and An. daciae (47.9%) were detected. In this study, An. daciae was documented for the first time in the two countries where it represented a markedly higher proportion of maculipennis complex species (with an overall prevalence almost reaching 50%) in comparison to previous reports from Germany, Romania and Poland. The determination of the differential distribution of maculipennis complex species will contribute to assessing risks of mosquito-borne diseases such as malaria or dirofilariasis.

How often do mosquitoes bite humans in southern England? A standardised summer trial at four sites reveals spatial, temporal and site-related variation in biting rates

BACKGROUND

This field-based study examined the abundance and species complement of mosquitoes (Diptera: Culicidae) attracted to humans at four sites in the United Kingdom (UK). The study used a systematic approach to directly measure feeding by mosquitoes on humans at multiple sites and using multiple volunteers. Quantifying how frequently humans are bitten in the field by mosquitoes is a fundamental parameter in assessing arthropod-borne virus transmission.

METHODS

Human landing catches were conducted using a standardised protocol by multiple volunteers at four rural sites between July and August 2013. Collections commenced two hours prior to sunset and lasted for a total of four hours. To reduce bias occurring due to collection point or to the individual attractiveness of the volunteer to mosquitoes, each collection was divided into eight collection periods, with volunteers rotated by randomised Latin square design between four sampling points per site. While the aim was to collect mosquitoes prior to feeding, the source of blood meals from any engorged specimens was also identified by DNA barcoding.

RESULTS

Three of the four sites yielded human-biting mosquito populations for a total of 915 mosquitoes of fifteen species/species groups. Mosquito species composition and biting rates differed significantly between sites, with individual volunteers collecting between 0 and 89 mosquitoes (over 200 per hour) of up to six species per collection period. Coquillettidia richiardii (Ficalbi, 1889) was responsible for the highest recorded biting rates at any one site, reaching 161 bites per hour, whilst maximum biting rates of 55 bites per hour were recorded for Culex modestus (Ficalbi, 1889). Human-biting by Culex pipiens (L., 1758) form pipiens was also observed at two sites, but at much lower rates when compared to other species.

CONCLUSIONS

Several mosquito species are responsible for human nuisance biting pressure in southern England, although human exposure to biting may be largely limited to evening outdoor activities. This study indicates Cx. modestus can be a major human-biting species in the UK whilst Cx. pipiens f. pipiens may show greater opportunistic human-biting than indicated by earlier studies.

Blood-feeding patterns of native mosquitoes and insights into their potential role as pathogen vectors in the Thames estuary region of the United Kingdom

BACKGROUND

The range of vertebrate hosts on which species of mosquito blood-feed is an important parameter for identifying potential vectors and in assessing the risk of incursion and establishment of vector-borne pathogens. In the United Kingdom, studies of mosquito host range have collected relatively few specimens and used techniques that could only broadly identify host species. This study conducted intensive collection and analysis of mosquitoes from a grazing marsh environment in southeast England. This site provides extensive wetland habitat for resident and migratory birds and has abundant human nuisance biting mosquitoes. The aim was to identify the blood-feeding patterns of mosquito species present at the site which could contribute to the transmission of pathogens.

METHODS

Twice-weekly collections of mosquitoes were made from Elmley Nature Reserve, Kent, between June and October 2014. Mosquitoes were collected using resting boxes, by aspiration from man-made structures and using a Mosquito Magnet Pro baited with 1-octen-3-ol. Blood-fed specimens were classified according to the degree of blood meal digestion using the Sella scale and vertebrate origin determined using sequencing of a fragment of the mitochondrial cytochrome C oxidase subunit I gene. Mosquitoes that were morphologically cryptic were identified to species level using multiplex PCR and sequencing methods.

RESULTS

A total of 20,666 mosquitoes of 11 species were collected, and 2,159 (10.4%) were blood-fed (Sella scale II-VI); of these 1,341 blood-fed specimens were selected for blood meal analysis. Vertebrate origin was successfully identified in 964 specimens (72%). Collections of blood-fed individuals were dominated by Anopheles maculipennis complex (73.5%), Culiseta annulata (21.2%) and Culex pipiens form pipiens (10.4%). Nineteen vertebrate hosts comprising five mammals and 14 birds were identified as hosts for mosquitoes, including two migratory bird species. Feeding on birds by Culex modestus and Anopheles atroparvus populations in England was demonstrated.

CONCLUSIONS

This study expands the vertebrate host range of mosquitoes in the Thames estuary region of the UK. Feeding on both resident and migratory bird species by potential arbovirus vectors including Cx. pipiens f. pipiens and Cx. modestus indicates the potential for enzootic transmission of an introduced arbovirus between migratory and local bird species by native mosquito species.

Distribution of individual members of the mosquito Anopheles maculipennis complex in Germany identified by newly developed real-time PCR assays

Owing to their role as vectors of malaria parasites, species of the Anopheles maculipennis complex (Diptera: Culicidae) Meigen were intensively studied in the past, but with the disappearance of malaria in Germany in the middle of the last century, the interest in this field of research declined. A comprehensive ecological analysis of the current species distribution for Germany is lacking. Between 2010 and 2013, a total of 1445 mosquitoes of the An. maculipennis complex were collected at 72 different sites in Germany. The samples comprise 722 single individuals as well as 723 individuals in 90 pools of up to 25 mosquitoes. All samples were analysed with newly developed species-specific qPCR assays for the identification of the four German species using nucleotide differences within the internal transcribed spacer 2 (ITS2) ribosomal DNA. All gathered data were used for species distribution modelling. The overall prevalence of An. messeae s.l. was highest with 98.89% of all pools; An. daciae with 6.93% of all individuals and An. messeae s.s. with 69.53%. The prevalence of the other two species was relatively low: An. maculipennis s.s. with 13.30% of all individuals (6.67% of all pools) and An. atroparvus with 1.80% of all individuals (1.11% of all pools).

Host preferences in host-seeking and blood-fed mosquitoes in Switzerland

The avian zoonotic agent for West Nile virus (WNV) can cause neuroinvasive disease in horses and humans and is expanding its range in Europe. Analyses of the risk for transmission to these hosts in non-endemic areas are necessary. Host preferences of mosquitoes (Diptera: Culicidae), the main vectors of WNV, were determined in Switzerland using animal-baited trap (horse, chickens) experiments at a natural and a periurban site. This was undertaken on four occasions during May-September 2014. In addition, the hosts of 505 blood-fed mosquitoes collected in a zoo and in the field were determined. Mosquito data obtained in the animal bait experiments were corrected for host weight and body surface area and by Kleiber's scaling factor. Collections of 11-14 different mosquito species were achieved with these approaches. Statistically significant host preferences were identified in three species in both approaches. The other species showed opportunistic feeding behaviours to varying extents. Specifically, the invasive species Hulecoeteomyia japonica (= Aedes japonicus) was identified for the first time as feeding on avians in nature. Abundance data, spatiotemporal activity and laboratory vector competence for WNV suggested that, in addition to the main WNV vector Culex pipiens, H. japonica and Aedimorphus vexans (= Aedes vexans) are the most likely candidate bridge vectors for WNV transmission in Switzerland.

Identification of blood meals in field captured sand flies by a PCR-RFLP approach based on cytochrome b gene

Leishmaniasis is a vector-borne disease transmitted by phlebotomine sand flies. Information about blood meal preferences in sand flies is essential to understand the epidemiology of the disease to adopt control measures. In previous studies, a polymerase chain reaction (PCR) of 359bp fragment of the conserved gene cytochrome b (cyt b) and further sequencing were applied in the study of blood meal sources in sand flies collected in the area of a leishmaniasis outbreak in southwest Madrid, Spain, providing significant information about blood meal preferences in the focus. In this work, a PCR-restriction fragment length polymorphism (RFLP) targeting a fragment of 359bp of vertebrate cyt b gene was developed. Restriction endonucleases HaeIII and HinfI generated specific patterns consistent with the blood meal sources found in sand flies. The protocol has been validated with twenty six engorged females collected in the field with CDC traps. Blood meals from nine vertebrates were identified based on PCR-cyt b and sequencing-human, dog, cat, horse, hare, rabbit, sheep, goat and chicken - and mixed blood meals (sheep/human; sheep/goat) - and successfully distinguished by PCR-RFLP. Therefore, this approach is an efficient and reliable alternative method to be applied in entomological surveys.

Molecular species identification, host preference and detection of myxoma virus in the Anopheles maculipennis complex (Diptera: Culicidae) in southern England, UK

BACKGROUND

Determining the host feeding patterns of mosquitoes by identifying the origin of their blood-meals is an important part of understanding the role of vector species in current and future disease transmission cycles. Collecting large numbers of blood-fed mosquitoes from the field is difficult, therefore it is important to maximise the information obtained from each specimen. This study aimed to use mosquito genome sequence to identify the species within Anopheles maculipennis sensu lato (An. maculipennis s.l.), identify the vertebrate hosts of field-caught blood-fed An. maculipennis s.l. , and to test for the presence of myxoma virus (Poxviridae, genus Leporipoxvirus) in specimens found to have fed on the European rabbit (Oryctolagus cuniculus).

METHODS

Blood-fed An. maculipennis s.l. were collected from resting sites at Elmley Nature Reserve, Kent, between June and September 2013. Hosts that An. maculipennis s.l. had fed on were determined by a PCR-sequencing approach based on the partial amplification of the mitochondrial cytochrome C oxidase subunit I gene. Mosquitoes were then identified to species by sequencing a region of the internal transcribed spacer-2. DNA extracts from all mosquitoes identified as having fed on rabbits were subsequently screened using PCR for the presence of myxoma virus.

RESULTS

A total of 94 blood-fed Anopheles maculipennis s.l. were collected, of which 43 (46%) provided positive blood-meal identification results. Thirty-six of these specimens were identified as Anopheles atroparvus, which had fed on rabbit (n = 33, 92%) and cattle (n = 3, 8%). Seven mosquitoes were identified as Anopheles messeae, which had fed on cattle (n = 6, 86%) and dog (n = 1, 14%). Of the 33 An. atroparvus that contained rabbit blood, nine (27%) were positive for myxoma virus.

CONCLUSIONS

Results demonstrate that a single DNA extract from a blood-fed mosquito can be successfully used for molecular identification of members of the An. maculipennis complex, blood-meal identification, and for the targeted detection of a myxoma virus. This study shows that An. atroparvus has a strong feeding preference for both healthy and myxoma-infected rabbits, providing evidence that this species may play a significant role in the transmission of myxomatosis among wild rabbit populations in the United Kingdom (UK).

Identifying biotic interactions which drive the spatial distribution of a mosquito community

Background

Spatial variation in the risk of many mosquito-borne pathogens is strongly influenced by the distribution of communities of suitable vector mosquitoes. The spatial distributions of such communities have been linked to the abiotic habitat requirements of each constituent mosquito species, but the biotic interactions between mosquitoes and other species are less well understood. Determining which fauna restrict the presence and abundance of key mosquito species in vector communities may identify species which could be employed as natural biological control agents. Whilst biotic interactions have been studied in the laboratory, a lack of appropriate statistical methods has prohibited the identification of key interactions which influence mosquito distributions in the field. Joint species distribution models (JSDMs) have recently been developed to identify biotic interactions influencing the distributions of species from empirical data.

Methods

We apply a JSDM to field data on the spatial distribution of mosquitoes in a UK wetland to identify both abiotic factors and biotic interactions driving the composition of the community.

Results

As expected, mosquito larval distributions in this wetland habitat are strongly driven by environmental covariates including water depth, temperature and oxidation-reduction potential. By factoring out these environmental variables, we are able to identify species (ditch shrimp of the genus Palaemonetes and fish) as predators which appear to restrict mosquito distributions.

Conclusions

JSDMs offer vector ecologists a way to identify potentially important biotic interactions influencing the distributions of disease vectors from widely available field data. This information is crucial to understand the likely effects of habitat management for vector control and to identify species with the potential for use in biological control programmes. We provide an R package BayesComm to enable the wider application of these models.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-0915-1) contains supplementary material, which is available to authorized users.

PCR identification and distribution of Anopheles daciae (Diptera, Culicidae) in Germany

Based primarily on nucleotide polymorphisms in the internal transcribed spacer 2 (ITS2) of the ribosomal DNA, Anopheles daciae was recently described as an additional member of the Maculipennis Group of species, separate from Anopheles messeae with which it had previously been confused due to morphological and genetic similarity. Species differentiation between A. messeae and A. daciae was possible only by ITS2 polymerase chain reaction (PCR) amplification followed by DNA sequencing or RFLP analysis. In addition to its siblings, Anopheles maculipennis, Anopheles atroparvus and A. messeae, A. daciae has been shown to occur in Germany, although with limited distribution. We here describe additional collection sites for this species in Germany, showing concentrations in East Germany and the northern Upper Rhine Valley in Southwest Germany. A species-specific multiplex PCR assay is presented that is able to differentiate the four Maculipennis Group sibling species occurring in Germany plus Anopheles sacharovi, Anopheles melanoon and Anopheles labranchiae. The correct identification and detailed knowledge of the biology of A. daciae are of relevance since it might be a vector of disease agents, as suggested by the vector potential of its siblings and the recent finding of an A. daciae female infected with Dirofilaria repens in southern Germany.