Heterogeneity of ITS1 sequences in the biting midge Culicoides impunctatus (Goetghebuer) suggests a population in Argyll, Scotland, may be genetically distinct

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.

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).

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.

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.

Molecular characterization of Swiss Ceratopogonidae (Diptera) and evaluation of real-time PCR assays for the identification of Culicoides biting midges

Biting midges of the genus Culicoides (Diptera, Ceratopogonidae) are vectors of several viruses of veterinary relevance, and they can cause insect bite hypersensitivity. As the morphological identification of these tiny insects is a difficult task in many cases, alternative approaches are expedient. With the aim to develop real-time PCRs, we determined partial mitochondrial cytochrome oxidase I gene (mt COI) sequences from 380 Culicoides midges representing three regions of Switzerland, namely the Alps, Midland north of the Alps (Atlantic climate), and South of the Alps (Mediterranean climate). The same region was also sequenced from non-biting midges of the genera Atrichopogon, Brachypogon, Dasyhelea, Forcipomyia and Serromyia. A total of 21 Culicoides species were identified by morphology. Sequence variability (haplotypes) was observed in all species. For each of C. grisescens and C. obsoletus, a novel cryptic species was identified. Whereas all individuals of C. grisescens and of the cryptic C. obsoletus species (O2) originated only from Alpine sites, the known C. obsoletus (O1) species was found in all three regions. Further, a sister taxon to C. pulicaris was identified based on the mt COI sequences and named Culicoides sp. Alignments of available mtCOI sequences from Ceratopogonidae (GenBank, this study) were used to design real-time PCR primers and probes to distinguish C. chiopterus, C. deltus, C. dewulfi, C. grisescens (including the cryptic species), C. imicola, C. lupicaris, C. obsoletus O1, C. obsoletus O2, C. pulicaris, C. scoticus and Culicoides sp. Specificities of primers and probes was tested with cloned targets representing 1 to 4 haplotypes of 18 Culicoides spp. and 1 haplotype each from 4 other Ceratopogonidae. No cross-reactivity was observed when plasmid template representing 5 × 10(6) gene copies was tested, but it was evident (Ct values ≤ 30) in few instances when plasmid template representing 5 × 10(9) gene copies was utilized, the latter corresponding to the total gene copy number (as determined in this study) in 20 insects. The sensitivities of two assays (C. imicola, C. grisescens) were tested by spiking single insects into pools of 99 or 999, randomly selected non-target Ceratopogonidae (with approx. 90% Culicoides specimens). In the pools of 100, Ct values were in the range of those obtained with single insects when employing 1% of the isolated DNA, whereas the sensitivity with the pools of 1000 was low, presumably due to the low DNA concentrations obtained with a protocol that seems inadequate for these larger pools. Thus, the assays as described are applicable for the specific identification of biting midges in small pools. Primers and probes of this study were devised to be suitable for multiplexed assays but these evaluations await to be performed.

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.

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

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) play important roles in the transmission of viral diseases affecting wild and domestic ruminants and horses, including Bluetongue (BT) and African horse sickness (AHS) respectively. In southern Europe, BT has been largely transmitted by the classical Afro-Asian vector Culicoides imicola Kieffer. However, other species such as C. obsoletus Meigen, C. scoticus Downs & Kettle and C. pulicaris Linné may also be involved in BTV transmission. As a consequence of the discovery of C. imicola followed by BTV-2 outbreaks on the island of Corsica in October 2000, further studies on these biting midges have been carried out. To better characterize the evolution and phylogenetic relations of Culicoides, molecular analysis in parallel with a morphology-based taxonomic approach were performed. Phylogenetic analyses of French Culicoides species were undertaken using the ribosomal DNA (rDNA) internal transcribed spacer 1 (ITS1) as a molecular target. This region was shown to be useful in understanding evolutionary and genetic relationships between species. Construction of several trees showed that molecular phylogeny within the genus Culicoides correlates not only with morphological-based taxonomy but also with ecological patterns.

Oral susceptibility to bluetongue virus of Culicoides (Diptera: Ceratopogonidae) from the United Kingdom

Oral susceptibility to infection with bluetongue virus (family Resviridae, genus Orbivirus, BTV) serotype 9 was characterized in three Palaearctic species of Culicoides (Diptera: Ceratopogonidae). Variation in susceptibility to infection by using a recently described feeding technique was shown to occur between populations of Culicoides obsoletus Meigen complex midges from different geographic regions of the United Kingdom with virus infection rates varying from 0.4 to 7.4% of those tested. Susceptibility to infection was consistent on an annual basis at selected sites. Prevalence of infection in the most susceptible populations of both the C. obsoletus and Culicoides pulicaris L. complexes was comparable with that of Culicoides imicola Kieffer, the major vector of BTV in southern Europe and throughout Africa, when using the same feeding method and virus. These results are discussed with reference to the potential threat of the virus to susceptible livestock in northern Europe.

Intragenomic heterogeneity of internal transcribed spacer rDNA in neotropical malaria vector Anopheles aquasalis (Diptera: Culicidae)

Intragenomic heterogeneity of the internal transcribed spacer (ITS) array was investigated in Anopheles aquasalis Curry mosquitoes from two geographic locations in each of Brazil and Venezuela, and one in Suriname. Polymerase chain reaction-amplified copies of the ITS were cloned and sequenced. The length of the entire array ranged from 782 to 990 bp, with most variation due to microsatellite insertions in ITS1. We detected 40 different ITSL sequences and 15 different ITS2 sequences of the 71 to 72 clones examined. The sequence divergence within localities ranged from 0.002 to 0.043 for ITS1 and from 0 to 0.006 for ITS2. Point mutations were common to both spacer regions, but dinucleotide microsatellite repeats were restricted to ITS1. Sequences from neither ITS1 nor ITS2 had a diagnostic distribution or were informative in distinguishing these populations, providing additional support for the status of An. aquasalis as a single species.