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

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.

Preliminary Study on Comparative Efficacy of Four Light Sources for Trapping Culicoides spp. (Diptera: Ceratopogonidae) in Prachuap Khiri Khan Province, Thailand

The light trap is an important tool to determine the presence and abundance of vectors in the field. However, no one has studied the efficiency of light traps for collecting Culicoides in Thailand. In the present study, the efficacy of four light sources was evaluated in Prachuap Khiri Khan province, Thailand. Incandescent (INCND) light, white fluorescent (WHT-FLR) light, ultraviolet fluorescent (UV-FLR) light, and UV light-emitting diode (UV-LED) light were tested using commercial traps. In total, 30,866 individuals of Culicoides species were collected from November 2020 to June 2021, of which 21,016 were trapped on site 1 and 6,731 were trapped on site 2. The two most abundant Culicoides species were C. imicola (54%) and C. oxystoma (31.2%). UV-FLR was highly effective, followed by UV-LED light, WHT-FLR light, and INCND light, respectively, for Culicoides collection. Significantly, more Culicoides species were collected in those traps baited with UV-FLR light, UV-LED light, or WHT-FLR light than for INCND light traps. Traps equipped with UV-FLR lights can be recommended to trap Culcoides biting midges for monitoring purposes.

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.

Dissecting the Species-Specific Virome in Culicoides of Thrace

Biting midges (Culicoides) are vectors of arboviruses of both veterinary and medical importance. The surge of emerging and reemerging vector-borne diseases and their expansion in geographical areas affected by climate change has increased the importance of understanding their capacity to contribute to novel and emerging infectious diseases. The study of Culicoides virome is the first step in the assessment of this potential. In this study, we analyzed the RNA virome of 10 Culicoides species within the geographical area of Thrace in the southeastern part of Europe, a crossing point between Asia and Europe and important path of various arboviruses, utilizing the Ion Torrent next-generation sequencing (NGS) platform and a custom bioinformatics pipeline based on TRINITY assembler and alignment algorithms. The analysis of the RNA virome of 10 Culicoides species resulted in the identification of the genomic signatures of 14 novel RNA viruses, including three fully assembled viruses and four segmented viruses with at least one segment fully assembled, most of which were significantly divergent from previously identified related viruses from the Solemoviridae, Phasmaviridae, Phenuiviridae, Reoviridae, Chuviridae, Partitiviridae, Orthomyxoviridae, Rhabdoviridae, and Flaviviridae families. Each Culicoides species carried a species-specific set of viruses, some of which are related to viruses from other insect vectors in the same area, contributing to the idea of a virus-carrier web within the ecosystem. The identified viruses not only expand our current knowledge on the virome of Culicoides but also set the basis of the genetic diversity of such viruses in the area of southeastern Europe. Furthermore, our study highlights that such metagenomic approaches should include as many species as possible of the local virus-carrier web that interact and share the virome of a geographical area.

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.

The effect of ambient temperature fluctuations on Culicoides biting midges population dynamics and activity in dairy farms: a longitudinal study

The effect of climatic factors on the presence of Culicoides Latreille (Diptera: Ceratopogonidae) was previously studied. Nevertheless, lack of laboratory rearing data hampers species-specific prediction of weather fluctuations effect on population size. To determine fluctuations in population size in the field, we recorded Culicoides and other Nematocerans in seven Israeli dairy farms over two-years (2011-2012) and analysed the association of their dynamics with fluctuations in ambient temperature and total rainfall. In six farms, the most abundant species were Culicoides imicola Kieffer and Culicoides schultzei (Enderlein) gp., primarily composed of parous females, and in one farm Culicoides obsoletus (Meigen) gp., mostly nulliparous females, were dominant. While the total number of insects was similar in both years, Culicoides numbers were significantly higher in 2012, but appeared later in the season and reached a higher peak. A multi-variable linear regression model demonstrated positive association of C. imicola and C. schultzei numbers with the monthly multi-annual ambient temperature and its specific deviation, but not with monthly rainfall. C. obsoletus populations peaked at spring and sharply decreased when temperature exceeded 20 °C, and were best modelled by adding quadratic terms. Weather-specific estimation of population size under field conditions may enable to predict outbreaks intensity of Culicoides-borne viruses.

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.

Seasonal and spatial variation in Culicoides community structure and their potential role in transmitting Simbu serogroup viruses in Israel

Culicoides biting midges (Diptera: Ceratopogonidae) are a successful group of small (1-3 mm) haematophagous flies, some species of which are biological vectors of veterinary arboviruses, such as bluetongue virus, epizootic haemorrhagic disease virus, African horse sickness virus and Simbu serogroup viruses. In this study, we examine seasonal and spatial effects on the presence and distribution of Culicoides communities associated with ruminant and equine farms in Israel, and their infection with Simbu serogroup viruses. Our results demonstrate that both the vectors and the viruses are widely spread in Israel, including regions that were previously considered Culicoides-free. Moreover, our results show that although seasonality affects infection with Simbu serogroup viruses, both viruses and potential vectors can be found year round, suggesting continuous circulation of Simbu serogroup viruses in Israeli livestock farms. Finally, this study provides novel and basic information on Simbu serogroup-infected Culicoides in Israel: it demonstrates that Sathuperi, Shuni and Peaton viruses were circulating in Israel in 2015-2017 as they were found in C. imicola and C. oxystoma, both potential vectors of these viruses, and supplies the first-ever genomic detection of Sathuperi in Israel. Consequently, the data emerging from this study are of importance in understanding the epidemiology of arboviruses in Israel and are of relevance to the potential spread and possible future outbreaks of different Simbu serogroup viruses within the Mediterranean region and Europe.

Oral Susceptibility of Japanese Culicoides (Diptera: Ceratopogonidae) Species to Akabane Virus

To test their virus susceptibility and capacity as transmission vectors, Japanese Culicoides species were artificially fed a mixture of Akabane virus (AKAV) and bovine blood, and virus recovery was attempted from infected midges 9-11 d post-exposure. Culicoides tainanus, C. punctatus, C. humeralis, C. jacobsoni, C. oxystoma, and C. asiana were found to be orally susceptible to AKAV. Virus titers in single infected midges of C. tainanus, C. oxystoma, C. punctatus, and C. jacobsoni ranged from 100.75 to 104.0 TCID50 (tissue culture infectious dose). The titers in the infected C. oxystoma were significantly higher than those in the other infected species. Viral RNA was detected from both midges testing positive and those testing negative for infectious virus particles, but the viral RNA copies in the infectious virus-negative midges were significantly lower than those in the infectious virus-positive midges. Lower viral amplification, limited dissemination or both caused by tissue barriers might occur in infected midges from which infectious viruses were undetectable. A fully disseminated infection was developed in orally infected C. oxystoma and C. tainanus. This finding indicates their capacity to transmit AKAV, assuming that salivary gland barriers have limited effects on viral entry to and replication in salivary gland tissue. This result also suggests that the other orally susceptible species are potentially competent for AKAV transmission and would be considered active vectors of its spread.

Overview and features of larval developmental sites of biting midges species associated with livestock in Israel with implications to their control

The larval developmental sites of Culicoides species were assessed from 1155 samples collected during the years 1969-2003. Culicoides circumscriptus was most prolific in mud with medium organic matter with proportional representation of 55.8%. Culicoides imicola breeds mainly in damp mixture of rotten, decomposed animal dung with or without some mud, with proportional representation of 97.2%. Culicoides obsoletus was found mostly in rotten banana stumps, with proportional representation of almost 100%. Culicoides puncticollis was found in mud with a medium amount of organic matter with proportional representation of 35.6%. Culicoides distinctipennis showed 22.2% proportional representation for mud poor in organic matter. Culicoides schultzei gr. was most prolifically in mud rich in organic matter with proportional representation of 6.2%. Culicoides cataneii was most prolifically in mud with a medium amount of organic matter with proportional representation of 1.8%. Maximum duration time to emergence from the larval developmental sites ranged from seven weeks in C. obsoletus to fourteen weeks in C. circumscriptus and nine weeks in C. imicola. All the studied species breed throughout the year. Significant innate differences in the proportions of the sexes were found in the emergence of six species.

Molecular differentiation and species composition of genus Culicoides biting midges (Diptera: Ceratopogonidae) in different habitats in southern China

Culicoides biting midges (Diptera:Ceratopogonidae) cause a significant biting nuisance to humans, livestock, which are the biological vectors of a range of risky pathogens. Accurate illustration of vector play a key role in arthropod borne diseases surveillance. However, few studies have focused on the Culicoides, which caused bluetongue disease in 29 provinces of China since 1979. In this study, we assessed cytochrome oxidase subunit I (COI) mtDNA molecular marker for identification of ten major vector species and analyzed the Culicoides species community and diversity in different habitats. A total of 20,795 Culicoides samples collected from 11 sample sites were identified as 23 species belonging to 7 subgenera. Sequences of COI gene worked well as barcodes for identifying all the determined specimen in this study and were comparable with the existing sequence data from GenBank. We first reported COI barcode sequences of C. morisitai, C. insignipennis and C. homotomus. Morphological identification of Culicoides spp. samples within southern China appears relatively robust and some unidentified species were required further study. Our study shows that the COI sequence data can be used as a tool to identify species of Culicoides in Jiangxi Province. In our sampled area, the most abundant species was C. arakawae (61.89%), followed by C. oxystoma (13.77%), C. punctatus (10.10%), C. nipponensis (8.82%), C. homotomus (3.19%) and C.morisitai (1.17%) in this study. C. punctatus was the dominant species of Park habitat (62.22%), C. arakawae was the predominant species of Chicken habitat (96.66%), Vegetable plot habitat (92.0%), and Peasant household habitat (83.21%), respectively. C. oxystoma was the abundant species of Residential area habitat (40.11%), Hospital habitat (56.65%), and Pig & Cow habitat (48.77%), respectively. Results also show that the potential Bluetongue virus vectors belong to the Obsoletus and Pulicaris groups, are also included and relatively abundant, notably: Culicoides punctatus. These findings expand the current knowledge of Culicoides population composition in the southern part of China.

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.

Foraging range of arthropods with veterinary interest: New insights for Afrotropical Culicoides biting midges (Diptera: Ceratopogonidae) using the ring method

The identification of blood meal source of arthropod vector species contributes to the understanding of host-vector-pathogen interactions. The aim of the current work was to identify blood meal source in Culicoides biting midge species, biological vectors of internationally important arboviruses of livestock and equids, using a new ecological approach. We examined the correlation between blood meal source identified in engorged Culicoides females collected in a suction light trap and the available vertebrate hosts along four rings (200, 500, 1000 and 2000 m) centered at the trap site and described the foraging range of the three main vector species of veterinary interest present in the study area, Culicoides imicola, Culicoides kingi and Culicoides oxystoma. The study was performed in four sites localized in the Niayes region of Senegal (West Africa) where recent outbreaks of African horse sickness occurred. Blood meal source identification was carried out by species-specific multiplex PCRs with genomic DNA extracted from the abdomen of engorged females collected during nine night collections for twenty-six collections. The four most abundant hosts present in the studied area (horse, cattle, goat and sheep) were surveyed in each ring zone. The blood meal source varied according to Culicoides species and host availability in each site. C. oxystoma and C. imicola females mainly fed on horses readily available at 200 m maximum from the trap location whereas females of C. kingi fed mainly on cattle, at variable distances from the traps (200 to 2000 m). C. oxystoma may also feed on other vertebrates. We discuss the results in relation with the transmission of Culicoides-borne arboviruses and the species dispersion capacities.

Host preferences and circadian rhythm of Culicoides (Diptera: Ceratopogonidae), vectors of African horse sickness and bluetongue viruses in Senegal

African horse sickness- and bluetongue virus are orbiviruses transmitted by Culicoides biting midges (Diptera: Ceratopogonidae) to horses and to ruminants, respectively. Since the last epizootic outbreak of African horse sickness in 2007 in Senegal, extensive investigations have been undertaken to improve our knowledge on Culicoides species involved locally in the transmission of the virus. The purpose of this study was to compare and quantify the host preferences of potential vectors of these orbiviruses on horse and sheep and to study their circadian rhythm. We found that Culicoides oxystoma and species of the sub-genus Avaritia (Culicoides imicola, Culicoides bolitinos and Culicoides pseudopallidipennis) had a preference for horse when compared to sheep (the predicted ratio between horse and sheep was 80 for C. oxystoma and 26 for C. imicola), and were mostly crepuscular: C. oxystoma had continuous activity throughout the diel with peaks in numbers collected after sunrise and sunset, while C. imicola was mostly nocturnal with peak after sunset. Unexpectedly, species of the subgenus Lasiohelea was also collected during this study. This diurnal biting species was a nuisance pest for both animal species used as bait.

Circadian activity of Culicoides oxystoma (Diptera: Ceratopogonidae), potential vector of bluetongue and African horse sickness viruses in the Niayes area, Senegal

Culicoides biting midges (Diptera: Ceratopogonidae) are important vectors of arboviruses in Africa. Culicoides oxystoma has been recently recorded in the Niayes region of Senegal (West Africa) and its high abundance on horses suggests a potential implication in the transmission of the African horse sickness virus in this region. This species is also suspected to transmit bluetongue virus to imported breeds of sheep. Little information is available on the biology and ecology of Culicoides in Africa. Therefore, understanding the circadian host-seeking activity of this putative vector is of primary importance to assess the risk of the transmission of Culicoides-borne pathogens. To achieve this objective, midges were collected using a sheep-baited trap over two consecutive 24-h periods during four seasons in 2012. A total of 441 Culicoides, belonging to nine species including 418 (94.8%) specimens of C. oxystoma, were collected. C. oxystoma presented a bimodal circadian host-seeking activity at sunrise and sunset in July and was active 3 h after sunrise in April. Daily activity appeared mainly related to time periods. Morning activity increased with the increasing temperature up to about 27 °C and then decreased with the decreasing humidity, suggesting thermal limits for C. oxystoma activity. Evening activity increased with the increasing humidity and the decreasing temperature, comprised between 20 and 27 °C according to seasons. Interestingly, males were more abundant in our sampling sessions, with similar activity periods than females, suggesting potential animal host implication in the facilitation of reproduction. Finally, the low number of C. oxystoma collected render practical vector-control recommendations difficult to provide and highlight the lack of knowledge on the bio-ecology of this species of veterinary interest.

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.

COI barcode based species-specific primers for identification of five species of stored-product pests from genus Cryptolestes (Coleoptera: Laemophloeidae)

Flat grain beetles of the genus Cryptolestes (Coleoptera: Laemophloeidae) are one of the economically most important stored-product pests which feed on many kinds of agricultural products, especially grains. Nine of more than 40 described Cryptolestes species are recognized as stored-product pests and two of the pest species have a cosmopolitan distribution. Given the rapid growth in global trade of food products, ecological barriers to the spread of pests are easily overcome. Therefore, development of reliable systems for routine quarantine inspection and early infestation detection is vital. In the present study, we established a new rapid and accurate cytochrome c oxidase subunit I-based system for molecular identification of five common stored-product Cryptolestes species, namely, Cryptolestes capensis, Cryptolestes ferrugineus, Cryptolestes pusilloides, Cryptolestes pusillus and Cryptolestes turcicus. Five species-specific primer pairs for traditional uniplex polymerase chain reaction assay are described and their specificity and sensitivity for the identification process is evaluated using larval samples of 12 different populations from three continents (Asia, Europe and North America).

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.

Culicoides (Diptera: Ceratopogonidae) midges, the vectors of African horse sickness virus--a host/vector contact study in the Niayes area of Senegal

BACKGROUND

African horse sickness (AHS) is an equine disease endemic to Senegal. The African horse sickness virus (AHSV) is transmitted to the mammalian hosts by midges of the Culicoides Latreille genus. During the last epizootic outbreak of AHS in Senegal in 2007, 1,169 horses died from this disease entailing an estimated cost of 1.4 million euros. In spite of the serious animal health and economic implications of AHS, very little is known about determinants involved in transmission such as contact between horses and the Culicoides species suspected of being its vectors.

METHODS

The monthly variation in host/vector contact was determined in the Niayes area, Senegal, an area which was severely affected by the 2007 outbreak of AHS. A horse-baited trap and two suction light traps (OVI type) were set up at each of five sites for three consecutive nights every month for one year.

RESULTS

Of 254,338 Culicoides midges collected 209,543 (82.4%) were female and 44,795 (17.6%) male. Nineteen of the 41 species collected were new distribution records for Senegal. This increased the number of described Culicoides species found in Senegal to 53. Only 19 species, of the 41 species found in light trap, were collected in the horse-baited trap (23,669 specimens) largely dominated by Culicoides oxystoma (22,300 specimens, i.e. 94.2%) followed by Culicoides imicola (482 specimens, i.e. 2.0%) and Culicoides kingi (446 specimens, i.e. 1.9%).

CONCLUSIONS

Culicoides oxystoma should be considered as a potential vector of AHSV in the Niayes area of Senegal due to its abundance on horses and its role in the transmission of other Culicoides-borne viruses.

Culicoides biting midges (Diptera, Ceratopogonidae) in various climatic zones of Russia and adjacent lands

Culicoides biting midges play an important role in the epidemiology of many vector-borne infections, including bluetongue virus, an internationally important virus of ruminants. The territory of the Russian Federation includes regions with diverse climatic conditions and a wide range of habitats suitable for Culicoides. This review summarizes available data on Culicoides studied in the Russian Federation covering geographically different regions, as well as findings from adjacent countries. Previous literature on species composition, ranges of dominant species, breeding sites, and host preferences is reviewed and suggestions made for future studies to elucidate vector-virus relationships.

Bunyavirus-vector interactions

The Bunyaviridae family is comprised of more than 350 viruses, of which many within the Hantavirus, Orthobunyavirus, Nairovirus, Tospovirus, and Phlebovirus genera are significant human or agricultural pathogens. The viruses within the Orthobunyavirus, Nairovirus, and Phlebovirus genera are transmitted by hematophagous arthropods, such as mosquitoes, midges, flies, and ticks, and their associated arthropods not only serve as vectors but also as virus reservoirs in many cases. This review presents an overview of several important emerging or re-emerging bunyaviruses and describes what is known about bunyavirus-vector interactions based on epidemiological, ultrastructural, and genetic studies of members of this virus family.

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.

First record of Culicoides oxystoma Kieffer and diversity of species within the Schultzei group of Culicoides Latreille (Diptera: Ceratopogonidae) biting midges in Senegal

The Schultzei group of Culicoides Latreille (Diptera: Ceratopogonidae) is distributed throughout Africa to northern Asia and Australasia and includes several potential vector species of livestock pathogens. The taxonomy of the species belonging to this species group is confounded by the wide geographical distribution and morphological variation exhibited by many species. In this work, morphological and molecular approaches were combined to assess the taxonomic validity of the species and morphological variants of the Schultzei group found in Senegal by comparing their genetic diversity with that of specimens from other geographical regions. The species list for Senegal was updated with four species: Culicoides kingi, C. oxystoma, C. enderleini and C. nevilli being recorded. This is the first record of C. oxystoma from Africa south of Sahara, and its genetic relationship with samples from Israel, Japan and Australia is presented. This work provides a basis for ecological studies of the seasonal and spatial dynamics of species of this species group that will contribute to better understanding of the epidemiology of the viruses they transmit.

Assessment of survival and body size variation of Culicoides imicola (Diptera: Ceratopogonidae) as functions of "Candidatus Cardinium" (Bacteroidetes) infection status

"Candidatus Cardinium hertigii" (Bacteroidetes) is a maternally inherited endosymbiont known from several arthropods. Its mechanisms for persistence in host populations are mostly reproductive manipulation, though it has been occasionally reported to improve fitness parameters in several hosts. In Culicoides (Diptera: Ceratopogonidae) biting midges, the prevalence of "Candidatus Cardinium" infection was documented as moderate, with no detectable sex bias. We therefore investigated whether "Candidatus Cardinium" affects important fitness parameters, such as survival and body size, in Culicoides imicola, a dominant vector species. Field-collected midges were trapped and analyzed for survival under different environmental conditions and antibiotic treatment, taking into account "Candidatus Cardinium" infection status and parity status (i.e., parous or nulliparous). Additionally, wing lengths were measured as a proxy parameter for body size and analyzed together with "Candidatus Cardinium" infection data. The findings revealed no difference in survival of Culicoides infected with "Candidatus Cardinium" and that of uninfected midges in both parity states and under all tested conditions: optimal, starvation, heat, and antibiotic treatment. Beyond survival, no wing length difference was found for "Candidatus Cardinium"-infected versus uninfected midges. In aggregate, these findings support our conclusion that "Candidatus Cardinium" does not have an overt effect on the survival and size of adult C. imicola midges. "Candidatus Cardinium" may affect immature stages or may alter adult reproductive performance.

Record of two species of Culicoides (Diptera, Ceratopogonidae) new for Madagascar and molecular study showing the paraphylies of the subgenus Oecacta and the Schultzei group

Culicoides are vectors of diseases of Veterinary Medicine importance (bluetongue, African horse sickness, Schmallenberg virus) all over the world. In the present study, we report two species new for Madagascar: C. nevilli and C. enderleini. They belong to the Schultzei group which is sometimes classified in the subgenus Oecacta and sometimes in the subgenus Remmia, depending on authors. Consequently, we carried out a molecular cladistics of these groups based on cytochrome C oxidase subunit I mtDNA sequences. We processed the Malagasy specimens and some C. furens (the Oecacta type-species) caught in Florida and we analyzed their sequences and those available in Genbank: C. schultzei, C. oxystoma, C. festivipennis, C. brunnicans, C. kibunensis, C. truncorum and C. vexans. C. (Avaritia) imicola have been selected as an outgroup. The maximum parsimony analysis showed the paraphylies of the Schultzei group (=Remmia) and of the subgenus Oecacta if the first group is excluded from the latter. Our results underline the doubtful current classification and need to be validated by other molecular markers in the future.

Prevalence of the symbiont Cardinium in Culicoides (Diptera: Ceratopogonidae) vector species is associated with land surface temperature

Prevalence of infection by bacterial symbionts may reflect their interactions with the host and has been shown to be correlated with environmental factors. Yet, it is still unclear whether infection by symbionts is determined by environmental factors affecting the early or imago stage of the host. Here, we identified and localized the symbiont Candidatus Cardinium hertigii (Bacteroidetes) in sympatric Culicoides biting midge species, examined its abundance, and studied its association with environmental factors. The prevalence of adult infection differed, with 50.7% from C. imicola, 31.4% from C. oxystoma, and 0% from C. schultzei gp., although phylogenetic analyses showed that Cardinium in these species is almost identical. In addition, prevalence of infection differed between climate regions, with lowest prevalence in the arid region and highest prevalence in the Mediterranean region. Multivariate linear regression analysis of Cardinium prevalence together with climatic and satellite imagery data-derived environmental variables revealed that infection prevalence is significantly associated with land surface temperature and explained up to 89.7% of infection prevalence variability. These findings suggest that the observed variation of Cardinium infection of the imago stage of Culicoides may be influenced by environmental conditions during the latter's early developmental stages.