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

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.

Wing morphology variations in Culicoides circumscriptus from France

The biting midge Culicoides circumscriptus Kieffer, 1918 is a European widespread vector of avian malaria throughout the continent and is a possible vector of Akabane virus and Bluetongue virus. This species populates a wide range of environments in contrasting ecological settings often exposed to strong seasonal fluctuations. The main goals of this study were to investigate C. circumscriptus phenotypic variation at three departments in France (Corsica Island, Moselle and Var) and to determine if its phenotypes vary with the environment. Culicoides circumscriptus wing phenotypes were analyzed using a geometric morphometric approach based on anatomical landmarks and outlines of the wing. Dendogram trees based on landmarks and the outlines-2 set (cell m4) showed similar topologies and separated populations of C. circumscriptus. In contrast, another set of outlines-1 (covering the r-m cross vein, M, radiale and arculus) presented a different hierarchical clustering tree. The phenotypic variation observed in C. circumscriptus indicated that these populations are exposed to environmental and ecological pressures. Our results suggest the presence of phenotypic plasticity in this species.

Assigning Culicoides larvae to species using DNA barcoding of adult females and phylogenetic associations

Background

Orbivirus-induced hemorrhagic diseases cause high mortality in wild and captive white-tailed deer in North America. The role of different Culicoides species in Orbivirus transmission outside of areas of intensive animal production has not been established. At our study location, bluetongue virus (BTV) RNA-positive female Culicoides debilipalpis pools have been detected annually since 2012 when BTV transmission was noted in a captive deer herd. Identifying specific larval habitats of suspected vectors at active transmission sites is crucial both for identifying the source of the vectors and for subsequently planning intervention actions. Since C. debilipalpis larvae are known to develop in tree holes, this study was designed to use DNA barcoding to identify larvae collected from tree holes.

Methods

Adult female Culicoides were collected using light or emergence traps and morphologically identified to 11 species. Culicoides sonorensis were also obtained from a laboratory colony. Substrate was collected from tree holes and flooded with water to harvest floating larvae. Total DNA from three to seven adult females per species and 19 larvae was extracted. Two loci of the nuclear 18S ribosomal RNA (rRNA) gene, one locus each of the mitochondrial cytochrome oxidase subunit I (COI) gene and the nuclear 28S rRNA gene were amplified using loci-specific primers.

Results

All 61 adults were sequenced at each of the four loci under study. Since no single locus delineated all putative species and the COI locus yielded unreliable pseudogenes for two individuals of C. arboricola, sequences of all four loci were concatenated to maximize species separation and allow for larval association with identified adults. Sixteen larvae were clearly assigned to species based on DNA barcoding and phylogenetic results. Multiple larvae were assigned to each of the C. debilipalpis clade, the C. villosipennis clade, the C. arboricola clade and the C. nanus clade.

Conclusions

Of the approximately 62 species described in the southeast USA, 21 have now been barcoded and sequences are publicly available. In this study, we constructed a database composed of species-specific sequences of adult Culicoides and then identified larvae to species by matching their corresponding sequences with adults. Since Culicoides larvae are difficult to identify, using DNA barcoding to facilitate larval habitat surveys can be a valuable tool.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05479-1.

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.

Composition and diversity of Culicoides biting midges (Diptera: Ceratopogonidae) in rural and suburban environments of Algeria

Culicoides biting midges are well known biological vectors of several arboviruses causing more than 100 veterinary and medical diseases worldwide. In Algeria, bluetongue virus, which is transmitted by Culicoides midges, is responsible for one of the most critical insect-borne diseases of sheep. For example, this disease caused clinically severe morbidity of about 2,661 confirmed cases out of 21,175 susceptible sheep in Algeria. This study compared the abundance, richness, and diversity of Culicoides species in rural and suburban environments of semi-arid regions in North Africa. It examined the potential influence of the bio-climatic factors on the variation of population sizes and the elevation distribution of biting midges. Specimen collection was carried out from June to September during two successive years (2018 and 2019) using CDC light traps installed at 15 sites in different environments. Culicoides specimens were dissected, slide-mounted, and morphologically identified using the interactive identification key IIKC and various standard morphological criteria. A total of 1,046 Culicoides specimens (1,024 females and 22 males) were trapped and classified into 22 species, belonged to nine distinct subgenera. Two new species records for Algeria and even North Africa are reported: Culicoides albicans (Winnertz, 1852) and Culicoides nubeculosus (Meigen, 1830). Culicoides newsteadi Austen, 1921 (51.6%) was the dominant species, and it was followed by Culicoides punctatus (Meigen, 1804) (16.3%) and Culicoides odiatus Austen, 1921 (11.5%). These three species, comprising 80% of the collected Culicoides, were the most abundant both outside and inside livestock stables in rural and suburban environments. Species diversity was similar in the two settings, with a slight increase in suburban environments. None of the Culicoides species encountered correlated significantly with the climatic factors (mean temperature, precipitation, and relative humidity). Elevation was the most determinant environmental parameter that affected the abundance and distribution of Culicoides midges in the semi-arid and sub-humid areas studied. The maximum distribution of Culicoides species was detected at mid elevations (400‒800 m). Using a modeling approach, we explored for the first time the variation of composition and diversity in Culicoides communities within different climatic regions, environments and livestock settings in Algeria. This survey deepens our understanding of the relationships among environmental factors, abundance, diversity, and geographic distribution of Culicoides. This is a crucial step to assess the epidemiological situation of the diseases transmitted by these biting midges and to allow mitigation of the associated risks.

Risk-based serological survey of bluetongue and the first evidence of bluetongue virus serotype 26 circulation in Tunisia

BACKGROUND

Bluetongue (BT), a vector-borne disease of wild and domestic ruminants, is responsible for severe economic losses in flocks. To reduce this impact, a surveillance and control plan was implemented in Tunisia. However, the epidemiological situation of BT remains incompletely understood, especially for the circulating serotypes.

OBJECTIVE

The aim of this survey was to determine the seroprevalence, to identify the circulating serotypes and to identify the associated risk factors for bluetongue virus (BTV) circulation in Tunisia using risk-based sampling (RBS).

METHODS

A total of 3314 blood samples were randomly collected from 67 sectors using risk-based sampling and screened by competitive enzyme-linked immunosorbent assays (c-ELISAs). Out of the 1330 positive samples, 200 samples were analysed by serum neutralization test (SNT) to identify circulating BTV serotypes.

RESULTS

Of 3314 sera, 1330 were c-ELISA-positive (40.1%) for antibodies against the BTV structural protein VP7. The result of SNT showed the presence of BTV-1, BTV-2, BTV-3, BTV-4 and, for the first time in Tunisia, BTV-26. The logistic regression model revealed that older animals had nearly two times the odds of being infected with BTV compared to younger animals. Flocks with a history of BT were almost 1.5 times more likely to be at risk for contracting BTV infection. The flock size, housing indoors and intensive production system were significant protective factors.

CONCLUSIONS

High seroprevalence of BTV among sheep was highlighted in Tunisia. The neutralization test showed the presence of the following BTV serotypes: BTV-1, BTV-2, BTV-3, BTV-4 and, for the first time in Tunisia, BTV-26. Age, production system and flock size were important variables associated with BTV infection in sheep. This finding is crucial, as it will allow the adjustment of the BT control programme in Tunisia.

Morphological and molecular differentiation between Culicoides oxystoma and Culicoides kingi (Diptera: Ceratopogonidae) in Tunisia

Background

Culicoides kingi and Culicoides oxystoma belong to the Schultzei group of biting midges. These two species are vectors of disease in livestock of economic importance. As described in the literature, morphological identification for discrimination between them is still unclear. However, species-specific identification is necessary to solve taxonomic challenges between species and to understand their roles in disease transmission and epidemiology. This study aims to develop accurate tools to discriminate C. oxystoma from C. kingi using traditional morphometry and polymerase chain reaction-restriction fragment length polymorphism (PCR RFLP) assays for use in developing countries.

Methods

Specimens were collected from the region of Kairouan in central Tunisia. A total of 446 C. oxystoma/C. kingi individuals were identified using traditional morphometric analyses combined with PCR–RFLP of the cytochrome c oxidase subunit I gene. Thirteen morphometric measurements were performed from the head, wings, and abdomen of slide-mounted specimens, and six ratios were calculated between these measurements. Multivariate analyses of the morphometric measurements were explored to identify which variables could lead to accurate species identification.

Results

Four variables, namely antennae, wings, spermathecae, and palpus length, were suitable morphometric characteristics to differentiate between the species. Digestion with the SspI restriction enzyme of the PCR product led to good discriminative ability. Molecular procedures and phylogenetic analysis confirmed the efficiency of this simple and rapid PCR–RFLP method.

Conclusions

This study highlights for the first time in Tunisia the presence of C. oxystoma and its discrimination from C. kingi using abdominal measurements and the PCR–RFLP method. This approach could be applied in future epidemiological studies at the national and international levels.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05084-8.

Towards modernizing the taxonomy of Mediterranean Culicoides using classical morphology, mtDNA barcoding, and MALDI-TOF MS protein profiling

Culicoides biting midges (Diptera: Ceratopogonidae) are a highly successful group of small (1-3 mm) hematophagous flies, infamous for the role they play as biological vectors for numerous pathogens of veterinary significance. The principal aim of the national animal disease surveillance program of Israel is to be able to rapidly sort and identify live field-captured insects including Culicoides for arbovirus screening. In this exploratory study, three identification methods-classical morphology, DNA barcoding, and MALDI-TOF MS-were applied simultaneously to individuals of 10 Culicoides species that commonly attack livestock in Israel. The strengths and limitations of the three methods are compared and evaluated. In essence, the CO1 barcoding and MALDI-TOF MS results closely matched those of classical morphology. Furthermore, at a higher level and in strong accordance with recognized subgenera, the 10 species, in the reconstructed phylogenies, coalesced into multiple deeper-branched monophyletic clades. However, some discrepancies between the molecular and protein profiling results did occur and proved difficult to assess in terms of taxonomic significance. This difficulty underscores how tricky it is to establish clear species limits when methods involving borderline cutoff values and similarity indices are used as a taxonomic aid. An added shortcoming of the pluralistic triple-method approach is that a significant percentage of the species-level depositions in the GenBank and BOLD databases are misidentified, hindering structured comparison and interpretation of the morphological and molecular results obtained. Aspects of the unresolved taxonomy of various biting midge assemblages within the Mediterranean basin, including minor changes to the Israeli Culicoides checklist, are discussed in light of the methods applied. It is observed that the direct access that classical morphology provides to the external environment (or species niche) is indispensable to the full and correct interpretation (and application) of concomitant molecular and protein profiling results. The Culicoides taxonomy of the future ought to be fully integrative, during which the assimilation of modern methodological advances should strengthen-rather than undermine-the morphological foundations laid down during the 260-year Linnaean epoch.

Update of the Culicoides (Diptera: Ceratopogonidae) species checklist from Algeria with 10 new records

BACKGROUND

The Culicoides fauna of Algeria has been historically investigated, leading to the description of many new species by Kieffer in the 1920s, Clastrier in the 1950s or Callot in the 1960s and to a comprehensive inventory by Szadziewski in the 1980s. The emergence of bluetongue in the late 1990s enhanced Culicoides collections made in the country over the last two decades, but information remained mostly unpublished. The aim of this study is therefore to provide a comprehensive and updated checklist of Culicoides biting midge species in Algeria.

METHODS

The literature (published and grey, in French and in English) from 1920 to date on Culicoides collections in Algeria was collected and analyzed in the light of the current taxonomic and systematic knowledge and methods. Fresh Culicoides material was also analyzed using light/suction trap collections carried out from November 2015 to September 2018 in nine localities of the 'wilayah' of Tiaret (northwestern Algeria). Slide mounted specimens were identified morphologically using the interactive identification key IIKC and original descriptions. Specimens were then compared with non-type material originating from different countries and partly with type material.

RESULTS

A total of 13,709 Culicoides, belonging to at least 36 species within 10 subgenera, were examined leading to 10 new records in Algeria, including C. chiopterus, C. dewulfi, C. navaiae, C. grisescens, C. paradoxalis, C. shaklawensis, C. simulator, C. univittatus, C. achrayi and C. picturatus. These new records and all previous records provided by the literature review were discussed.

CONCLUSIONS

We propose a Culicoides checklist for the Algerian fauna of 59 valid species, including species mainly with a large Palaearctic distribution and a specific Mediterranean distribution, and only a few species from the Afrotropical region. Among them, several species, mainly of the subgenera Avaritia and Culicoides, are confirmed or probable vectors of arboviruses important in animal health.

Updating the global occurrence of Culicoides imicola, a vector for emerging viral diseases

Culicoides imicola is the main vector transmitting viruses causing animal diseases such as Bluetongue, African Horse Sickness, and Schmallenberg. It has become widely distributed, with reports from South Africa to southern Europe, and from western Africa to southern China. This study presents a global compendium of Culicoides imicola occurrence between 1943 and 2018, reflecting the most recently compiled and harmonized global dataset derived from peer-reviewed literature. The procedures used in producing the data, as well as the geo-coding methods, database management and technical validation procedures are described. The study provides an updated and comprehensive global database of C. imicola occurrence, consisting of 1 039 geo-coded records from 50 countries. The datasets can be used for risk mapping of the diseases transmitted by C. imicola as well as to develop the global habitat suitability for the vector.

A survey of Onchocerca fasciata infection in camels (Camelus bactrianus) with notes on morphology

The goal of this study was to provide insight into the pathogenicity of Onchocerca fasciata in Camelus bactrianus to help control onchocerciasis. From November 2015 to January 2016, the prevalence and severity of onchocerciasis were recorded in 152 camels. Nodules containing Onchocerca were collected and observed. Adult parasites were extracted from the nodules and identified via light microscopy as well as by partial sequencing of the cytochrome oxidase subunit I (COI) gene. The sequences were examined and compared to similar sequences from other Onchocerca species. In total, 80.3% of camels were parasitized. The severity of infection varied, as camels harboured between one and fifteen nodules. The morphology and the cuticle differed in both sexes and displayed considerable variation in the thickness and structure of different body parts. Identification was further confirmed using molecular biology methods. This study provides a comprehensive morphological description of Onchocerca fasciata isolated from camels. The prevalence and intensity of infection (assessed via nodules) varied in the Bactrian camels. The structure of the cuticle was an important morphological feature for species differentiation in Onchocerca. Based on our data, the morphological assessment of O. fasciata represents a reliable method to characterize other Onchocerca species.

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.

Application of DNA barcoding for identifying forensically relevant Diptera from northern Thailand

In recent decades, forensic entomology has become a useful tool in criminal investigations all over the world. Species-specific identification of flies plays an important role in this field and is obligatory for accurate calculation of the post-mortem interval. However, not all important colonizers of a corpse can be identified by common morphological keys. Due to similar morphology and the lack of keys for some taxa, especially for immature stages, DNA barcoding has become more popular during the last recent years. This development is particularly important for countries like Thailand, in which forensic entomology is a newly developing research area and which faces several challenges such as a high biodiversity of fly species. The most commonly used barcoding region in forensic entomology, the mitochondrial cytochrome oxidase subunit 1 (coI) gene, as well as a 1000-bp-long region of the 28S nuclear rRNA gene, was used to analyze and establish the molecular barcodes of 13 different species of flies of forensic relevance in northern Thailand.

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.

Blood meal analysis of culicoides (Diptera: ceratopogonidae) in central Tunisia

To evaluate the host preferences of Culicoides species (Diptera: Ceratopogonidae) in Central Tunisia, we identified the source of blood meals of field collected specimens by sequencing of the cytochrome b (cyt b) mitochondrial locus and Prepronociceptine single copy nuclear gene. The study includes the most common and abundant livestock associated species of biting midges in Tunisia: C. imicola, C. jumineri, C. newsteadi, C. paolae, C. cataneii, C. circumscriptus, C. kingi, C. pseudojumineri, C. submaritimus, C. langeroni, C. jumineri var and some unidentified C. species. Analysis of cyt b PCR products from 182 field collected blood-engorged females' midges revealed that 92% of them fed solely on mammalian species, 1.6% on birds, 2.4% on insects and 0.8% on reptiles. The blast results identified the blood origin of biting midges to the species level with exact or nearly exact matches (≥98%). The results confirm the presence of several Culicoides species, including proven vectors in Central Tunisia. Blood meal analyses show that these species will indeed feed on bigger mammals, thereby highlighting the risk that these viruses will be able to spread in Tunisia.

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.