Phylogenetic analysis of Culicoides species from France based on nuclear ITS1-rDNA sequences

Shedding light on the controversial taxonomic status of Culicoides jamaicensis and Culicoides paolae (Diptera: Ceratopogonidae): an overseas trip among continents

Culicoides biting midges (Diptera: Ceratopogonidae) are small bloodsucking flies that act as vectors for various pathogens of medical and veterinary importance. This study aimed to examine, using a comprehensive approach, the controversial taxonomic status of 2 Culicoides species that are currently distributed in the Neotropical (Culicoides jamaicensis Edwards) and Palearctic (Culicoides paolae Boorman) areas and possess unique and distinctive features. Previous investigations based on morphological analysis have suggested that these 2 species may be synonyms. Our work updated the current geographical distribution of both species and analyzed new specimens from different geographic origins, together with publicly available sequences. We used 2 universal genetic markers (COI and 28S) to test this hypothesis. Our study reveals evidence that C. paolae and C. jamaicensis belong to the same species due to the following statements: (i) similar morphological features; (ii) low interspecific genetic variation; (iii) association with a single genetic cluster; (iv) inclusion within the subgenus Drymodesmyia, which has only been recorded in the New World; and (v) occurrence in habitats with moderate temperatures. We recommend that European and African specimens of C. paolae be considered from now on as C. jamaicensis. Our comprehensive approach shed new light on the taxonomic status of these 2 Culicoides species and has implications for future studies on their biology and ecology.

Molecular identification of Culicoides oxystoma and Culicoides actoni vectors of bluetongue virus

Bluetongue is a non-contagious viral disease causing significant economic losses throughout the world. The bluetongue vectors Culicoides oxystoma and Culicoides actoni, which play a significant role in the transmission of various pathogens, are distributed across different geographical realms. Adults are minute in size with wide phenotypic variation, so morphology-based species identification is severely constrained by preparatory time and shortage of taxonomic expertise. To make the identification process rapid and effective, a specific primer was designed for the identification of C. actoni based on the multiple sequence alignment of ITS1 sequences of 11 Culicoides species. Along with this, a refined version of existing C. oxystoma specific primer was proposed. The primer sets distinguished C. oxystoma and C. actoni from a pooled sample consisting of other Culicoides species as well as closely related genera such as Forcipomyia and Alluaudomyia. Our findings suggest that the primers were species specific, sensitive and have potential to discriminate vector species C. oxystoma and C. actoni from pooled samples. To the best of our knowledge, these are the first ITS1 sequences generated and submitted in GenBank for Culicoides innoxius, Culicoides shortti, Culicoides palpifer and Culicoides anophelis and the first for Culicoides peregrinus, Culicoides fulvus and C. actoni from India.

Morphological and Molecular Identification of Culicoides (Diptera: Ceratopogonidae) Species of the Southern California Desert

Culicoides Latreille (Diptera: Ceratopogonidae) biting midges are vectors of important animal pathogens including bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV). While some Culicoides species present in the southern California desert are implicated in the transmission of these viruses to ruminant animals, these species have not been extensively studied due in part to the challenge of identifying Culicoides to species and to the lack of published gene sequences for these species to support their molecular identification. In this study, Culicoides were captured using suction traps baited with either carbon dioxide or UV light from transitional habitat between the southern California peninsular mountain ranges and the Colorado desert of southeastern California. Captured midges were initially identified using traditional morphological methods, with species identification subsequently confirmed by sequence analysis of COI and 28S rDNA genes. Phylogenetic analyses support that some Culicoides subgenera are not monophyletic. Two recognized species (C. sitiens Wirth and Hubert and C. bakeri Vargas) shared the same COI and 28S sequences. An additional cryptic species may be present within C. sitiens. Two additional recognized species (C. cacticola Wirth and Hubert and C. torridus Wirth and Hubert) may be conspecific or cryptic to each other. In total, 19 Culicoides species (or species aggregate) were collected in this study, with genetic sequences published for the first time for 16 of them. Published genetic sequences will support future research on these species, including studies on the ecology and habits of their immature stages which are often tedious to identify using morphology.

A phylogenetic analysis of the biting midges belonging to Culicoides Latreille (Diptera: Ceratopogonidae) subgenus Avaritia using molecular data

Background

Within the genus Culicoides (Diptera: Ceratopogonidae), the subgenus Avaritia is of particular interest as it contains a significant number of economically important vector species. Disagreements about the systematic classification of species within this subgenus have resulted in a taxonomic imbroglio.

Methods

A molecular phylogeny of the subgenus Avaritia was conducted to test the existing systematic classification, which is based on phenetic assessment of morphological characters. Three nuclear ribosomal markers, internal transcribed spacer 1 and 2 (ITS1, ITS2), 5.8S, and three mitochondrial markers, cytochrome c oxidase subunit 1 and 2, and cytochrome b (cox1, cox2 and cytb), were obtained for 37 species of the subgenus Avaritia from all six biogeographical regions. Phylogenetic reconstructions using these genes independently and in combination were implemented using Bayesian inference analysis and maximum likelihood methods.

Results

Phylogenetic reconstructions gave strong support to several monophyletic groups within the subgenus Avaritia. Both C. actoni and C. pusillus formed a single clade with C. grahamii so their respective groups, the Actoni and Pusillus groups, have been merged with the Grahamii group. Some support was provided for the Boophagus and Jacobsoni groups. A group of species currently placed into the Orientalis group clustered in a clade with poor support. The Obsoletus group was defined as a sister clade to all other Avaritia groups. The clade including the Imicola group was well supported based on phylogenetic criteria.

Conclusions

This phylogenetic study combining five distinct molecular markers has provided meaningful insights into the systematic relationships of Culicoides (Avaritia) and highlighted future directions to continue the study of this subgenus. While the cox2 marker appeared to be useful to investigate closely related species, the 5.8S marker was highly conserved and uninformative. Further investigations including species absent from this work are needed to confirm the proposed systematic scheme. However, this systematic scheme can now serve as a foundation to investigate cryptic species affiliation within the subgenus. We advocate that future studies employ a combination of morphological and molecular analyses.

Diagnosing bluetongue virus in domestic ruminants: current perspectives

This review provides an overview of current and potential new diagnostic techniques against bluetongue virus (BTV), an Orbivirus transmitted by arthropods that affects ruminants. Bluetongue is a disease currently notifiable to the World Organization for Animal Health (OIE), causing great economic losses due to decreased trade associated with bluetongue outbreaks and high mortality and morbidity. BTV cross-reacts with many antigenically related viruses including viruses that causes African Horse sickness and epizootic haemorrhagic disease of deer. Therefore, reliable diagnostic approaches to detect BTV among these other antigenically related viruses are used or being developed. The antigenic determinant for differentiation of virus species/serogroups among orbiviruses is the VP7 protein, meanwhile VP2 is serotype specific. Serologically, assays are established in many laboratories, based mainly on competitive ELISA or serum neutralization assay (virus neutralization assay [VNT]) although new techniques are being developed. Virus isolation from blood or semen is, additionally, another means of BTV diagnosis. Nevertheless, most of these techniques for viral isolation are time-consuming and expensive. Currently, reverse-transcription polymerase chain reaction (RT-PCR) panels or real-time RT-PCR are widely used methods although next-generation sequencing remains of interest for future virus diagnosis.

Molecular phylogeny of 42 species of Culicoides (Diptera, Ceratopogonidae) from three continents

The genus Culicoides includes vectors of important animal diseases such as bluetongue and Schmallenberg virus (BTV and SBV). This genus includes 1300 species classified in 32 subgenera and 38 unclassified species. However, the phylogenetic relationships between different subgenera of Culicoides have never been studied. Phylogenetic analyses of 42 species belonging to 12 subgenera and 8 ungrouped species of genus Culicoides from Ecuador, France, Gabon, Madagascar and Tunisia were carried out using two molecular markers (28S rDNA D1 and D2 domains and COI mtDNA). Sequences were subjected to non-probabilistic (maximum parsimony) and probabilistic (Bayesian inference (BI)) approaches. The subgenera Monoculicoides, Culicoides, Haematomyidium, Hoffmania, Remmia and Avaritia (including the main vectors of bluetongue disease) were monophyletic, whereas the subgenus Oecacta was paraphyletic. Our study validates the subgenus Remmia (= Schultzei group) as a valid subgenus, outside of the subgenus Oecacta. In Europe, Culicoides obsoletus, Culicoides scoticus and Culicoides chiopterus should be part of the Obsoletus complex whereas Culicoides dewulfi should be excluded from this complex. Our study suggests that the current Culicoides classification needs to be revisited with modern tools.

DNA barcoding and surveillance sampling strategies for Culicoides biting midges (Diptera: Ceratopogonidae) in southern India

Background

Culicoides spp. biting midges transmit bluetongue virus (BTV), the aetiological agent of bluetongue (BT), an economically important disease of ruminants. In southern India, hyperendemic outbreaks of BT exert high cost to subsistence farmers in the region, impacting on sheep production. Effective Culicoides spp. monitoring methods coupled with accurate species identification can accelerate responses for minimising BT outbreaks. Here, we assessed the utility of sampling methods and DNA barcoding for detection and identification of Culicoides spp. in southern India, in order to provide an informed basis for future monitoring of their populations in the region.

Methods

Culicoides spp. collected from Tamil Nadu and Karnataka were used to construct a framework for future morphological identification in surveillance, based on sequence comparison of the DNA barcode region of the mitochondrial cytochrome c oxidase I (COI) gene and achieving quality standards defined by the Barcode of Life initiative. Pairwise catches of Culicoides spp. were compared in diversity and abundance between green (570 nm) and ultraviolet (UV) (390 nm) light emitting diode (LED) suction traps at a single site in Chennai, Tamil Nadu over 20 nights of sampling in November 2013.

Results

DNA barcode sequences of Culicoides spp. were mostly congruent both with existing DNA barcode data from other countries and with morphological identification of major vector species. However, sequence differences symptomatic of cryptic species diversity were present in some groups which require further investigation. While the diversity of species collected by the UV LED Center for Disease Control (CDC) trap did not significantly vary from that collected by the green LED CDC trap, the UV CDC significantly outperformed the green LED CDC trap with regard to the number of Culicoides individuals collected.

Conclusions

Morphological identification of the majority of potential vector species of Culicoides spp. samples within southern India appears relatively robust; however, potential cryptic species diversity was present in some groups requiring further investigation. The UV LED CDC trap is recommended for surveillance of Culicoides in southern India.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1722-z) contains supplementary material, which is available to authorized users.

Population Genetic Structure and Potential Incursion Pathways of the Bluetongue Virus Vector Culicoides brevitarsis (Diptera: Ceratopogonidae) in Australia

Culicoides brevitarsis is a vector of the bluetongue virus (BTV), which infects sheep and cattle. It is an invasive species in Australia with an assumed Asian/South East Asian origin. Using one mitochondrial marker (i.e., part of the cytochrome oxidase subunit I gene) and six nuclear markers, we inferred population genetic structure and possible incursion pathways for Australian C. brevitarsis. Nine mitochondrial haplotypes, with low nucleotide sequence diversity (0.0–0.7%) among these, were identified in a sample of 70 individuals from seven sites. Both sets of markers revealed a homogeneous population structure, albeit with evidence of isolation by distance and two genetically distinct clusters distributed along a north-to-south cline. No evidence of a cryptic species complex was found. The geographical distribution of the mitochondrial haplotypes is consistent with at least two incursion pathways into Australia since the arrival of suitable livestock hosts. By contrast, 15 mitochondrial haplotypes, with up to four times greater nucleotide sequence diversity (0.0–2.9%) among these, were identified in a sample of 16 individuals of the endemic C. marksi (sampled from a site in South Australia and another in New South Wales). A phylogenetic tree inferred using the mitochondrial marker revealed that the Australian and Japanese samples of C. brevitarsis are as evolutionarily different from one another as some of the other Australian species (e.g., C. marksi, C. henryi, C. pallidothorax) are. The phylogenetic tree placed four of the species endemic to Australia (C. pallidothorax, C. bundyensis, C. marksi, C. henryi) in a clade, with a fifth such species (C. bunrooensis) sharing a common ancestor with that clade and a clade comprising two Japanese species (C. verbosus, C. kibunensis).

Taxonomic assessment of Culicoides brunnicans, C. santonicus and C. vexans (Diptera: Ceratopogonidae) in France: Implications in systematics

Culicoides brunnicans Edwards, 1939, Culicoides santonicus, Callot et al., 1966, and Culicoides vexans (Staeger, 1839) belong to the Vexans group of the subgenus Oecacta. These species had never been studied by molecular methods and their distribution in Western Europe overlapped. C. brunnicans and C. santonicus are two closely related species and their diagnoses are based on the wing pattern only. An integrative taxonomic approach was conducted on females of the Vexans group, Culicoides furens (the type species of the subgenus Oecacta), and Culicoides nubeculosus (as outgroup) using sequences of D1D2 rDNA domains, sequences of COI mtDNA, and wing morphometrics. Species of the Vexans group were discriminated by all traits, and were closely related in the phylogeny. Their taxonomic status and their relation to C. furens were re-evaluated.

Culicoides Latreille (Diptera: Ceratopogonidae) taxonomy: current challenges and future directions

Culicoides Latreille biting midges (Diptera: Ceratopogonidae) cause a significant biting nuisance to humans, livestock and equines, and are the biological vectors of a range of internationally important pathogens of both veterinary and medical importance. Despite their economic significance, the delimitation and identification of species and evolutionary relationships between species within this genus remains at best problematic. To date no phylogenetic study has attempted to validate the subgeneric classification of the genus and the monophyly of many of the subgenera remains doubtful. Many informal species groupings are also known to exist but few are adequately described, further complicating accurate identification. Recent contributions to Culicoides taxonomy at the species level have revealed a high correlation between morphological and molecular analyses although molecular analyses are revealing the existence of cryptic species. This review considers the methods for studying the systematics of Culicoides using both morphological and genetic techniques, with a view to understanding the factors limiting our current understanding of Culicoides biology and hence arbovirus epidemiology. In addition, we examine the global status of Culicoides identification, highlighting areas that are poorly addressed, including the potential implementation of emerging technologies.

Worldwide niche and future potential distribution of Culicoides imicola, a major vector of bluetongue and African horse sickness viruses

We modelled the ecoclimatic niche of Culicoides imicola, a major arthropod vector of midge-borne viral pathogens affecting ruminants and equids, at fine scale and on a global extent, so as to provide insight into current and future risks of disease epizootics, and increase current knowledge of the species' ecology. Based on the known distribution and ecology of C. imicola, the species' response to monthly climatic conditions was characterised using CLIMEX with 10′ spatial resolution climatic datasets. The species' climatic niche was projected worldwide and under future climatic scenarios. The validated model highlights the role of irrigation in supporting the occurrence of C. imicola in arid regions. In Europe, the modelled potential distribution of C. imicola extended further West than its reported distribution, raising questions regarding ongoing process of colonization and non-climatic habitat factors. The CLIMEX model highlighted similar ecological niches for C. imicola and the Australasian C. brevitarsis raising questions on biogeography and biosecurity. Under the climate change scenarios considered, its' modelled potential distribution could expand northward in the Northern hemisphere, whereas in Africa its range may contract in the future. The biosecurity risks from bluetongue and African horse sickness viruses need to be re-evaluated in regions where the vector's niche is suitable. Under a warmer climate, the risk of vector-borne epizootic pathogens such as bluetongue and African horse sickness viruses are likely to increase as the climate suitability for C. imicola shifts poleward, especially in Western Europe.

Phenotypic differentiation and phylogenetic signal of wing shape in western European biting midges, Culicoides spp., of the subgenus Avaritia

In the past decade biting midges of the subgenus Avaritia (Diptera: Ceratopogonidae) have been popular subjects of applied entomological studies in Europe owing to their implication as biological vectors in outbreaks of bluetongue and Schmallenberg viruses. This study uses a combination of cytochrome oxidase subunit I barcode sequencing and geometric morphometric analyses to investigate wing shape as a means to infer species identification within this subgenus. In addition the congruence of morphological data with different phylogenetic hypotheses is tested. Five different species of the subgenus Avaritia were considered in the study (C. obsoletus (Meigen); C. scoticus Kettle and Lawson; C. chiopterus (Meigen); C. dewulfi Goetghebuer and C. imicola (Kieffer)). The study demonstrated that over 90% of individuals could be separated correctly into species by their wing shape and that patterns of morphological differentiation derived from the geometric morphometric analyses were congruent with phylogenies generated from sequencing data. Morphological data produced are congruent with monophyly of the subgenus Avaritia and the exclusion of C. dewulfi from the group containing C. obsoletus, C. scoticus and C. chiopterus. The implications of these results and their importance in a wider context of integrating multiple data types to interpret both phylogeny and species characterization is discussed.

Species determination of Culicoides biting midges via peptide profiling using matrix-assisted laser desorption ionization mass spectrometry

Background

Culicoides biting midges are vectors of bluetongue and Schmallenberg viruses that inflict large-scale disease epidemics in ruminant livestock in Europe. Methods based on morphological characteristics and sequencing of genetic markers are most commonly employed to differentiate Culicoides to species level. Proteomic methods, however, are also increasingly being used as an alternative method of identification. These techniques have the potential to be rapid and may also offer advantages over DNA-based techniques. The aim of this proof-of-principle study was to develop a simple MALDI-MS based method to differentiate Culicoides from different species by peptide patterns with the additional option of identifying discriminating peptides.

Methods

Proteins extracted from 7 Culicoides species were digested and resulting peptides purified. Peptide mass fingerprint (PMF) spectra were recorded using matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) and peak patterns analysed in R using the MALDIquant R package. Additionally, offline liquid chromatography (LC) MALDI-TOF tandem mass spectrometry (MS/MS) was applied to determine the identity of peptide peaks in one exemplary MALDI spectrum obtained using an unfractionated extract.

Results

We showed that the majority of Culicoides species yielded reproducible mass spectra with peak patterns that were suitable for classification. The dendrogram obtained by MS showed tentative similarities to a dendrogram generated from cytochrome oxidase I (COX1) sequences. Using offline LC-MALDI-TOF-MS/MS we determined the identity of 28 peptide peaks observed in one MALDI spectrum in a mass range from 1.1 to 3.1 kDa. All identified peptides were identical to other dipteran species and derived from one of five highly abundant proteins due to an absence of available Culicoides data.

Conclusion

Shotgun mass mapping by MALDI-TOF-MS has been shown to be compatible with morphological and genetic identification of specimens. Furthermore, the method performs at least as well as an alternative approach based on MS spectra of intact proteins, thus establishing the procedure as a method in its own right, with the additional option of concurrently using the same samples in other MS-based applications for protein identifications. The future availability of genomic information for different Culicoides species may enable a more stringent peptide detection based on Culicoides-specific sequence information.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-3305-7-392) contains supplementary material, which is available to authorized users.

Biting midges monitoring (Diptera: Ceratopogonidae: Culicoides Latreille) in the governate of Monastir (Tunisia): species composition and molecular investigations

The results of entomological studies carried out in the governate of Monastir (Tunisia) in 2009-2010 (captures and emergences from muds) focusing on Culicoides species are presented in the present study. Identification of Culicoides at the species level is based on morphological characters, and a molecular study has been carried out based on mitochondrial DNA cytochrome C oxidase I gene (COI) and D1 and D2 domains of the 28S rDNA. The DNA sequences reported here are related to 10 species (on 25 known) of Culicoides described in Tunisia: Culicoides cataneii-gejgelensis, Culicoides circumscriptus, Culicoides imicola, Culicoides jumineri, Culicoides kingi, Culicoides langeroni, Culicoides newsteadi, Culicoides paolae, Culicoides puncticollis and Culicoides sahariensis. DNA sequencing of the COI gene and D1D2 domains discriminated all morphologically determined species. The choice of D1D2 domains considered as a conserved region is informative for Culicoides species identification. The molecular analyses of COI has grouped both C. circumscriptus, C. puncticollis within two clusters and C. newsteadi within five subclusters. However, C. newsteadi shows relatively deep intraspecific divergence using COI sequences.

Characterization of two cryptic species, Culicoides stigma and C.parroti (Diptera: Ceratopogonidae), based on barcode regions and morphology

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are insect vectors of economically important veterinary diseases such as African horse sickness, bluetongue, and Schmallenberg virus. The identification of Culicoides based on morphological features can be difficult. Three species of biting midges, Culicoides nubeculosus, C. stigma, and C. parroti have emerged in the laboratory from mud collected around watering troughs on a farm in northern France. Emerging Culicoides were characterized morphologically and molecularly using molecular markers. The closely related species C. stigma and C.parroti showed highly divergent sequences for both mitochondrial (cytochrome B and cytochrome oxidase I) and ribosomal DNA first internal transcribed spacer. A RFLP based on a single restriction using the same enzyme (HaeIII) for both cytochrome C oxidase I and cytochrome B is proposed to identify these species.

Wing geometry as a tool for discrimination of Obsoletus group (Diptera: Ceratopogonidae: Culicoides) in France

In Europe, Culicoides chiopterus, Culicoides dewulfi, Culicoides obsoletus and Culicoides scoticus, which belongs to the subgenus Avaritia and Obsoletus group are the most proficient Bluetongue and Schmallenberg vectors. Within this group, correct identification based on morphological traits is difficult but essential to assess disease transmission risk. The development of new tools has revolutionized taxonomy (i.e. geometric morphometrics and molecular biology). Wing morphology is of primary importance to entomologists interested in systematics. Here, we report phenotypic differentiation patterns among the species above mentioned using a landmark-based geometric morphometric approach that efficiently identified C. chiopterus and C. dewulfi. Wing shape of the C. scoticus sample exhibited large specific variability. Based on landmarks and phylogenetic analyses (Maximum Parsimony), we suggest that Obsoletus group in Europe includes only C. obsoletus and C. scoticus. C. dewulfi and C. chiopterus are clearly excluded. Their shape seems closer to C. obsoletus that is why we suggest that only these two species should be grouped in the Obsoletus group. In addition, the concordance between phenetic clusters and phylogenies inferred from molecular data based on a fragment of the mtDNA COI gene and rDNA 28S suggests the existence of a strong signal in wing shape. These findings encourage us to use this powerful tool in taxonomic studies.

Differential emergence of Culicoides (Diptera: Ceratopogonidae) from on-farm breeding substrates in Northern Ireland

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are vectors of a number of viral diseases worldwide. Following the unforeseen outbreak of bluetongue in northern Europe (2006–2009) there was a need to clarify on-farm breeding substrates utilized by temperate Culicoides spp. Six substrates (cow dung, cow slurry, horse dung, sheep dung, maize silage and soil) were investigated for Culicoides spp. emergence over a 31-week period. Overall, most Obsoletus group Culicoides emerged from the cow dung and the most Pulicaris group Culicoides emerged from the sheep dung. Furthermore, Culicoides of the Obsoletus group were found to be abundant in cow slurry and sheep dung. Temperature played a significant role in the emergence times of adult Culicoides. The Obsoletus group appear to have undergone 3 generations during the experimental period. The sex ratio of emergent Obsoletus group Culicoides was affected by substrate type, with a greater proportion of males emerging from cow dung and slurry compared with the other substrates.

Barcoding of biting midges in the genus Culicoides: a tool for species determination

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are insect vectors of economically important veterinary diseases such as African horse sickness virus and bluetongue virus. However, the identification of Culicoides based on morphological features is difficult. The sequencing of mitochondrial cytochrome oxidase subunit I (COI), referred to as DNA barcoding, has been proposed as a tool for rapid identification to species. Hence, a study was undertaken to establish DNA barcodes for all morphologically determined Culicoides species in Swedish collections. In total, 237 specimens of Culicoides representing 37 morphologically distinct species were used. The barcoding generated 37 supported clusters, 31 of which were in agreement with the morphological determination. However, two pairs of closely related species could not be separated using the DNA barcode approach. Moreover, Culicoides obsoletus Meigen and Culicoides newsteadi Austen showed relatively deep intraspecific divergence (more than 10 times the average), which led to the creation of two cryptic species within each of C. obsoletus and C. newsteadi. The use of COI barcodes as a tool for the species identification of biting midges can differentiate 95% of species studied. Identification of some closely related species should employ a less conserved region, such as a ribosomal internal transcribed spacer.

Molecular identification of field-collected Culicoides larvae in the southern part of Japan

Although Culicoides biting midges act as a vector of important human and domestic animal diseases, their ecology is poorly understood. The lack of proper identification systems of Culicoides larvae is one of the main obstacles to progress in research. Based on mitochondrial sequences of 19 Japanese Culicoides species, we designed a universal primer set to amplify the partial sequence of the mitochondrial cytochrome c oxidase I (cox 1). The polymerase chain reaction product amplified from extracted DNA of Culicoides larvae using the primer set was directly sequenced, and species identification based on the variation at cox1 was conducted. Using the molecular identification system, we sorted 243 specimens of field-collected larvae from the southern part of Japan into 10 species including Culicoides arakawae (Arakawa), Culicoides oxystoma Kieffer, and Culicoides brevitarsis Kieffer, which are regarded as vectors of important livestock animal diseases. Eight species of Culicoides larvae, including C. arakawae and C. oxystoma, were recovered from active paddy fields and an abandoned paddy field. The result suggests that paddy fields contribute to breeding a variety of Culicoides species and maintenance and spread of Culicoides-borne pathogens. In contrast, larvae of C. brevitarsis were collected from cattle dung in pastures. The molecular identification system described herein using nucleotide sequences successfully achieved larval identification and will be useful for a better understanding of larval habitats of Culicoides biting midges.

Comparative study of antennal and maxillary palp olfactory sensilla of female biting midges (Diptera: Ceratopogonidae: Culicoides) in the context of host preference and phylogeny

Culicoides biting midges (Diptera Ceratopogonidae) are vectors of disease, including bluetongue and African horse sickness. Host preference of these insects is primarily regulated by olfactory cues, detected by olfactory sensilla on the antennae and maxillary palps. In this study, we analyzed the sensillum repertoire of biting midge species with known host preferences. Five different morphological sensillum types, sensilla trichodea, s. chaetica, s. ampullacea, s. coeloconica, and grooved peg sensilla, were present on the antennae of all species. In addition sensilla basiconica were present on the maxillary palps. We found that the numbers of short blunt-tipped s. trichodea, s. coeloconica, and s. basiconica are significantly higher in the ornithophilic Culicoides festivipennis (Kieffer) compared with the mammalophilic Culicoides obsoletus (Meigen) and Culicoides chiopterus (Meigen). In contrast, we found that the mammalophilic Culicoides pulicaris (L.) and the opportunistic Culicoides punctatus (Meigen) have intermediate numbers of these sensillum types. Comparison with available data from other species strongly suggests that these differences in the number of specific sensillum types, in general, are a reflection of host preference and not of phylogeny. We discuss the putative function of the individual sensillum types in relation to host volatile detection.

Molecular identification, phylogenetic status, and geographic distribution of Culicoides oxystoma (Diptera: Ceratopogonidae) in Israel

Culicoides oxystoma (Diptera: Ceratopogonidae) is an important vector species, reported mainly from Asia, with high potential to transmit viral diseases affecting livestock. In Japan, many arboviruses have been isolated from C. oxystoma, suggesting it as a key player in the epidemiology of several Culicoides-borne diseases. Over the years, C. oxystoma has also been reported in the Middle East region, including Israel. In this region, however, C. oxystoma cannot be easily distinguished morphologically from its sibling species included in the Culicoides schultzei complex. We therefore used genomic data for species identification and phylogeny resolution. Phylogenetic analyses based on internal transcribed spacer 1 (ITS-1) of ribosomal DNA and the mitochondrial gene encoding cytochrome oxidase subunit I (COI) showed that C. oxystoma from Israel is closely related to C. oxystoma from Japan. Using differential probing PCR, we showed that C. oxystoma is distributed all over the country, especially in Mediterranean climate regions. Culicoides oxystoma is less common or even absent in arid regions, while the other genetic cluster of C. schultzei complex was found only in the east of the country (mostly arid and semiarid regions). The molecular finding of C. oxystoma in wide geographical regions, together with its high proportion in the general Culicoides population and its vectoring potential, imply that it may be an important vector species in the Middle East.

Morphological and molecular identification of species of the Obsoletus group (Diptera: Ceratopogonidae) in Scandinavia

After the introduction of bluetongue in northern Europe in 2006, populations of Culicoides have been monitored in many European countries. Large quantities of Culicoides specimens shall be determined to species, and it is thus important to find reliable morphological characters that are visualized in a stereomicroscope. Culicoides obsoletus, Culicoides scoticus, Culicoides chiopterus, and Culicoides dewulfi all belonging to subgenus Avaritia are common in collections in northern Europe. C. obsoletus and C. scoticus often make up more than 50% of the total catch of biting midges. Separation of the females of the four species by morphological characters has frequently been questioned, and in many cases, female specimens are grouped as an entity in veterinary and ecological studies. We show how it is possible using a stereomicroscope to separate the females of the four species by combining the shape of the third segment of the maxillary palp and the number and location of hairs on the first abdominal tergit. Validation of the quick stereomicroscope identification method was achieved by morphometric measurements and a molecular marker. In all cases, both methods verified the quick morphological species identification of the Obsoletus group females. In conclusion, the females of all four species of the Obsoletus group can be separated by a quick morphological method under the stereomicroscope.

Suggesting synonymies? Comments on Kiehl et al. (2009) "the European vectors of Bluetongue virus: are there species complexes, single species or races in Culicoides obsoletus and C. pulicaris detectable by sequencing ITS-1, ITS-2 and 18S-rDNA?"

Species recognition and identification are crucial in any biological studies, especially when dealing with insect species involved in pathogen transmission. In recent years, molecular approaches have helped the clarification of systematic schemes and taxonomic status. Kiehl et al. (Parasitol Res 105:331-336, 2009) used molecular data to discuss the taxonomic status of biting midge species in the Palaearctic region. In the present work, the statements that "[Thus] there is no molecular support for the existence of a separate species C. montanus" and "[Therefore] probably C. scoticus should be considered only as a race of C. obsoletus" are discussed.

Variations in the mitochondrial cytochrome c oxidase subunit I gene indicate northward expanding populations of Culicoides imicola in Spain

Culicoides imicola is the main vector for bluetongue (BT) and African horse sickness (AHS) viruses in the Mediterranean basin and in southern Europe. In this study, we analysed partial mitochondrial cytochrome c oxidase subunit I (COI) gene to characterize and confirm population expansion of Culicoides imicola across Spain. The data were analysed at two hierarchical levels to test the relationship between C. imicola haplotypes in Spain (n = 215 from 58 different locations) and worldwide (n = 277). We found nineteen different haplotypes within the Spanish population, including 11 new haplotypes. No matrilineal subdivision was found within the Spanish population, while western and eastern Mediterranean C. imicola populations were very structured. These findings were further supported by median networks and mismatch haplotype distributions. Median networks demonstrated that the haplotypes we observed in the western Mediterranean region were closely related with one another, creating a clear star-like phylogeny separated only by a single mutation from eastern haplotypes. The two, genetically distinct, sources of C. imicola in the Mediterranean basin, thus, were confirmed. This type of star-like population structure centred around the most frequent haplotype is best explained by rapid expansion. Furthermore, the proposed northern expansion was also supported by the statistically negative Tajima's D and Fu's Fs values, as well as predicted mismatch distributions of sudden and spatially expanding populations. Our results thus indicated that C. imicola population expansion was a rapid and recent phenomenon.

Genetic diversity of ribosomal RNA internal transcribed spacer sequences in Lutzomyia species from areas endemic for New World cutaneous leishmaniasis

In this study, each of 60 rRNA internal transcribed spacer (ITS) 1 and ITS2 sequences was determined from 44 individuals of 14 morphologically identified New World sand fly Lutzomyia species in Ecuador, and their interspecies and intraspecies genetic diversity was compared. Distinguishing between related species based on the ITS1 sequence was difficult because of variability, while the genetic diversity of ITS2 was distinct even among closely related species. Further, an assessment of intraspecies ITS sequence diversity in the subgenus Helcocyrtomyia revealed no correlation between sequence variation and geographic distribution. The results strongly suggested ITS2 to be a more suitable marker than ITS1 for the taxonomic analysis of Lutzomyia species including closely related species. Moreover, neither ITS sequence may be useful for the analysis of population structures in Lutzomyia species.

Characterization of internal transcribed spacer (ITS1)-ITS2 region of ribosomal RNA gene from 25 species of Culicoides biting midges (Diptera: Ceratopogonidae) in Japan

We determined nucleotide sequences of the nuclear rDNA internal transcribed spacer (ITS)1-5.8S-ITS2a-2S-ITS2 region in 103 individuals of 25 Culicoides species (Diptera: Ceratopogonidae) from 11 locations in Japan. Ribosomal RNA genes, 5.8S and 2S rDNA, were highly conserved among the species with few variations. The ITS2a region showed length variation among species. Both ITS1 and ITS2 showed highly varied sequences among species. The noticeable indel regions among ITS1 sequences are present in some Culicoides species, separating species into two types having long or short ITS1 region. However, Culicoides cylindratus Kitaoka possesses both types of ITS1 in each individual; these results seem to indicate that the ITS1-long type was the prototype and the short type was produced through deletion in many Culicoides species. One species, belonging to subgenus Avaritia, possessed an Avaritia-specific sequence in ITS1 and phylogenetically formed a monophyletic group. Geographical genotypes in a species were not clear. Species-specific sequence features were observed, enabling molecular identification of Culicoides species.

Generalized structure and evolution of ITS1 and ITS2 rDNA in black flies (Diptera: Simuliidae)

A sample of 15 Nearctic black fly species spread over five genera is used to perform the first systematic study of the internal transcribed spacer 1 (ITS1) from the nuclear rDNA transcription unit of Simuliidae. ITS1 from the Prosimuliini tribe is a conserved, repeat-free and highly structured sequence of about 490 nucleotides (nt), while Simuliini exhibit a medium-sized or short version, the latter minimally 95 nt long. All size versions possess a common 39 nt core made from eight short blocks interspersed among highly variable sequences. Conversely, that variability which generally excludes ITS1 from phylogenetic applications translates for many species into polymorphisms suggesting the general feasibility of ITS1-based population studies. We show in a parallel investigation that ITS2, the other rDNA transcribed spacer, is length-constrained around 270 nt and possesses a three-domain fold anchored by four conserved regions representing about 40% of the whole sequence. An alignment guided by this secondary structure leads to a phylogeny, derived through the GTR model, which convincingly displays the basal divergence between Simuliini and Prosimuliini. However, the poorer support of some intermediate nodes could indicate rapid divergence events within Simulium.

Phylogenetic analysis indicates that Culicoides dewulfi should not be considered part of the Culicoides obsoletus complex

Analysis of DNA sequence data has proven invaluable for defining the relationships among taxa, as well as resolving their evolutionary histories. Here, we analyzed DNA sequence variation of one mitochondrial gene (COI) and two nuclear regions (ITSI and II) to clarify the phylogenetic position of Culicoides dewulfi, a midge species widely spread in Europe and a suspected vector for bluetongue virus. Various authors have described C. dewulfi either as part of the Culicoides obsoletus sensu lato complex or as a separate taxonomic group. A maximum likelihood phylogeny, based upon an optimal model of sequence evolution, placed C. dewulfi outwith the C. obsoletus s.l. complex. Shimodaira-Hasegawa test highlighted that this topology was significantly more likely than any topology that placed C. dewulfi anywhere else in the phylogeny. As such, C. dewulfi should not be considered part of the C. obsoletus s.l. complex and instead be treated as a separate group, phylogenetically close to the classical Old World vector C. imicola.

Biting rates of Culicoides midges (Diptera: Ceratopogonidae) on sheep in northeastern Spain in relation to midge capture using UV light and carbon dioxide-baited traps

Biting midges in the genus Culicoides (Diptera: Ceratopogonidae) were collected near sunset by direct aspiration from sheep in northeastern Spain to determine species-specific biting rates and crepuscular activity. Midges were also collected by UV-baited light traps and CO2-baited traps over the same period to compare species diversity and abundance using these common surveillance methods to actual sheep attack rates. Culicoides aspirated from sheep included C. obsoletus, C. parroti, C. scoticus, C. punctatus, and C. imicola. Peak host-seeking activity during the time period examined for the two most commonly collected species (C. obsoletus and C. parroti) occurred just before sunset and activity ceased within 1 h after sunset. Host attack rates near sunset averaged 0.9 midges/min for both species with maximum attack rates of 3/min for C. obsoletus and 4/min for C. parroti. For both species, approximately 35% of midges collected from the sheep were engorged, giving a maximum biting rate of 1.1/min for C. obsoletus and 1.5/min for C. parroti. Traps baited with CO2 collected fewer midges of each species relative to other collection methods. Traps baited with UV light provided a good indication of species richness but significantly underestimated the host attack rate of C. obsoletus and C. parroti while overestimating the host attack rate of C. imicola. Animal-baited collecting is critical to interpret the epidemiological significance of light trap collections used for surveillance of the midge vectors of bluetongue virus and African horse sickness virus.

The European vectors of Bluetongue virus: are there species complexes, single species or races in Culicoides obsoletus and C. pulicaris detectable by sequencing ITS-1, ITS-2 and 18S-rDNA?

When studying the vectorship of Culicoides species during the outbreak of Bluetongue disease (BTD) in Central Europe, the question arose whether the most common species and additionally proven vectors of BTV (C. obsoletus and C. pulicaris) are definitive species or do they belong to so-called complexes, since the determination based on morphological criteria is not very significant and knowledge on the life cycles is poor or even absent. Therefore, the present molecular biological study on their ITS-1, ITS-2 and 18SrDNA characteristics was initiated to investigate specimens, which had been determined by their wing morphology during an entomological monitoring in the years 2007 and 2008 at 91 farms in Germany (Mehlhorn et al. 2009). This study revealed novel types respectively different forms, which appeared very similar to Culicoides obsoletus, but showed slightly varying wing patterns. The molecular biological data were compared to those in data banks and combined to provisional dendrograms. The ITS-1 and ITS-2 analysis showed that the specimens determined in the monitoring as C. obsoletus inclusive those with different wing pattern correlate significantly with the data of C. obsoletus in the data banks and surrounded the data bank specifications of C. montanus and C. scoticus so closely that the latter might be only hardly separate species. A similar interpretation can also be drawn when looking at the 18S rDNA dendrogram. Thus, C. scoticus and C. montanus might be races of C. obsoletus rather than separate species. With respect to the ITS-1 and ITS-2 characteristics of C. pulicaris females, which morphologically and by size can be significantly differentiated from C. obsoletus, it was seen that this species is significantly situated on another rame of the dendrograms and in very close relationship to C. punctatus and C. lupicaris, so that the latter might also be only races of C. pulicaris. One of the two other most common species found in Northrhine-Westfalia-C. festivipennis-belongs to the rame of the dendrogram, where C. pulicaris is situated close to C. circumscriptus, while the other common species (C. nubeculosus) has its place close to C. puncticollis and C. variipennis on the rame, where C. obsoletus is found. Thus, this paper again clearly points out that the question "what is a definite species" is far from being solved, if the life cycle is not defined and morphology misleading. However, it also became clear that C. obsoletus and C. pulicaris are Europe-wide occurring species and that several other clearly described separate species are probably only races.

Changes of the abundance of Culicoides obsoletus s.s. and Culicoides scoticus in Southwest Germany identified by a PCR-based differentiation

The outbreak of bluetongue disease in Central Europe necessitates new approaches in the identification of vectors to follow-up changes of populations of species and not of complexes. Since females of species of the complex of Culicoides obsoletus are difficult to be identified according to morphological criteria, we applied a polymerase chain reaction (PCR)-based strategy targeting the mitochondrial cytochrome oxidase subunit I to differentiate between the species Culicoides obsoletus s.s. and Culicoides scoticus. Catches of culicoids obtained from May to November 2007 in an ultraviolet lamp trap at a cattle farm in Rhineland-Palatinate, Southern Germany were surveyed for changes of the abundance of both species. Only in May 2007, the samples contained similar proportions of both species. Afterwards, C. scoticus dominated with up to 88%. Calculating the number of specimens of both species within the total catches of culicoids, the numbers of C. obsoletus s.s. slightly decreased from May to July and increased to a little maximum in August. C. scoticus seemed to have three maxima in this period of time, the strongest one in August, presumably due to different generations and not to climatic conditions. These results indicate that the applied PCR strategy can be used for a detailed analysis of culicoids as basis for the estimation of the transmission risk of the bluetongue virus by different species of the Obsoletus complex.

PCR identification of Culicoides dewulfi midges (Diptera: Ceratopogonidae), potential vectors of bluetongue in Germany

Due to the severe outbreaks of bluetongue disease (BTD) in the years 2006/2007 in Germany in the absence of the main African vector Culicoides imicola, a rapid and easy applicable method for identification of autochthonous Culicoides spp. had to be developed. Morphological identification is time-consuming, rendering impossible the identification of large numbers of midges in a short period of time. A polymerase chain reaction (PCR)-based procedure in connection with a species-specific primer greatly simplifies the identification process. The region of internal transcribed spacer 1 (ITS-1) of the ribosomal DNA has shown great potential for developing a reliable PCR-based procedure. Culicoides midges were caught with ultraviolet-light traps installed on different farms in Germany during 2007 and 2008. The midges were mounted on slides and morphologically characterised. Midge DNA was extracted and the ITS-1 region amplified using conservative primers. Potential primer regions within ITS-1 were determined and a species-specific Culicoides dewulfi primer was developed to correctly identify autochthonous C. dewulfi, one of the suspected BTV vectors in northwestern Europe. The developed primer was used to identify C. dewulfi in a pool of Culicoides midges from a farm in the state of Brandenburg.

Development and evaluation of a real-time quantitative PCR assay for Culicoides imicola, one of the main vectors of bluetongue (BT) and African horse sickness (AHS) in Africa and Europe

The current microscopy method for identifying the Culicoides imicola Kieffer, 1913 species can be time and labour intensive. There is a need for the development of a rapid and quantitative tool to quantify the biting midges C. imicola ss in light trap catches. A reproducible and sensitive real-time polymerase chain reaction method that targets the internal transcribed spacer (ITS-1) of ribosomal DNA of C. imicola ss species was developed. This real-time PCR assay was first performed on 10-fold serial dilutions of purified plasmid DNA containing specific C. imicola ss ITS-1. It was then possible to construct standard curves with a high correlation coefficient (r2=0.99) in the range of 10(-2)-10(-8) ng of purified DNA. The performances of this PCR were evaluated in comparison with morphological determination on Culicoides trapped along the Mediterranean coastal mainland France. ROC statistical analysis was carried out using morphology as gold standard and the area under the ROC curve had a satisfactory value of 0.9752. The results indicated that this real-time PCR assay holds promise for monitoring C. imicola ss population in both surveillance and research programmes because of its good specificity (92%) and sensitivity (95%).

Influence of biotic and abiotic factors on the distribution and abundance of Culicoides imicola and the Obsoletus Complex in Italy

Culicoides imicola Kieffer (Culicoides, Diptera: Ceratopogonidae) is the principal vector of bluetongue virus (BTV) to ruminant livestock in southern Europe. The secondary potential vectors are Culicoides obsoletus (Meigen) and Culicoides scoticus Downes and Kettle of the Obsoletus Complex, Culicoides pulicaris (Linnaeus) of the Pulicaris Complex and Culicoides dewulfi Goetghebuer of the subgenus Avaritia Fox. Between 2000 and 2004 >38,000 light-trap collections were made for Culicoides across Italy including the islands of Sardinia and Sicily. Mapping of the 100 largest collections of C. imicola and of the Obsoletus Complex showed them to be disjunct overlapping in only 2% of the 200 municipalities selected. For each municipality the average values were calculated for minimum temperature, aridity index, altitude, terrain slope, normalised difference vegetation index (NDVI) and percentage forest cover. A factor analysis identified two principal factors ('biotic' and 'abiotic') and explained 84% of the total variability; a discriminant analysis classified correctly 87.5% of the observations. The results indicate adult populations of C. imicola to occur in more sparsely vegetated habitats that are exposed to full sunlight, whereas species of the Obsoletus Complex favour a more shaded habitat, with increased green leaf density. Heliophily and umbrophily, by shortening or lengthening the respective adult life cycles of these two vectors, will likely impact on the ability of each to transmit BTV and is discussed in the light of the current outbreak of BTV across the Mediterranean Basin.

Molecular identification of Western European species of obsoletus complex (Diptera: Ceratopogonidae) by an internal transcribed spacer-1 rDNA multiplex polymerase chain reaction assay

In southern Europe, orbiviral diseases such as bluetongue (BT) have been assumed to have been largely transmitted by the classical Afro-Asian vector Culicoides imicola Kieffer (Diptera: Ceratopogonidae). Recent outbreaks have occurred in regions where C. imicola is normally absent, supporting the theory that other species belonging to the Obsoletus or Pulicaris complexes may play a role in BT virus transmission. Investigations of the ecology of the species within the former group are hampered by females of member species being extremely difficult to separate by classical morphology. To allow straightforward separation of these species in France, a multiplex polymerase chain reaction-based on internal transcribed spacer (ITS)-1 rDNA was developed to distinguish between Culicoides chiopterus Meigen, Culicoides dewulfi Goetghebuer, Culicoides montanus Shakirjanova, Culicoides obsoletus Meigen, and Culicoides scoticus Downes & Kettle. This tool will be useful in defining both the vector role and larval biotopes of these species in Europe.