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

Culicoides species of Palaearctic region in Afrotropical region: comments on two recent publications on Culicoides species present in Ethiopia

Biting midges are key vectors that can transmit different pathogens to mammals and birds. In Ethiopia, two studies showed the diversity of Culicoides species in several districts based on morphological characters. For this, the same identification key was used for Afrotropical and Palaearctic Culicoides fauna. Consequently, results are incomplete and erroneous. It is misleading to state that a universal identification key is available.

DNA barcoding and host blood meal identification of Culicoides Latreille (Diptera, Ceratopogonidae) from Malaysia

Mitochondrial cytochrome oxidase I (COI) sequences were used to determine the genetic diversity and species identification efficacy of Culicoides from Malaysia. In total, 100 COI sequences were obtained from 13 morphologically identified species. Intraspecific genetic divergence varied from 0.48 % in C. parahumeralis to 14.88 % in C. palpifer. However, most (8 of 13) had low (<3 %) intraspecific genetic divergence. Identification of these species based on best match (BM) and best close match (BCM) methods revealed a high efficiency of the COI sequences with 100 % and 99 % success for BM and BCM, respectively. Identification in the BOLD database revealed that 10 species were successfully determined and agreed with morphological identifications. There remained three taxa which were ambiguous (C. jacobsoni) or had no species level identity match (C. palpifer and C. flavescens). Phylogenetic analyses found that all Malaysian specimens were clustered with conspecifics except C. palpifer. Specimens of this taxon separated into two divergent clades, one with members of a BIN (BOLD:ADT9601) of C. palpifer whereas the other formed a novel genetic lineage. Molecular species delimitation identified the morphologically identified species of the Malaysian Culicoides in the respective species. The exceptions were two divergent lineages found in C. palpifer because they were treated as two different taxa. Molecular identification of the host blood meal source revealed that all were from water buffalo (Bubalus bubalis).

An atlas of wing photographs and a key to species of the genus Culicoides Latreille from Mexico (Diptera: Ceratopogonidae), including new records, new synonymy, two new species and new status of Culicoides neghmei Vargas and C. propinquus Macfie

An atlas of wing photographs and a key to 91 species of biting midges in the genus Culicoides from Mexico. Culicoides (Diphaomyia) evansi Wirth & Blanton from Morelos and C. (Drymodesmyia) pilosus Wirth & Blanton from Hidalgo are recorded from Mexico. Two new species from Chiapas are described and illustrated, Culicoides ostotlae sp. nov. in the Daedalus group and Culicoides tzotzil sp. nov. in the subgenus Diphaomyia. We proposed a new status for Culicoides neghmei Vargas in the Limai group, which is closely related to C. luglani Jones & Wirth, and C. propinquus Macfie to be included in the subgenus Drymodesmyia. Culicoides wirthomyia Vargas is now a junior synonym of C. jamaicensis Edwards.

Exceptional Bluetongue virus (BTV) and Epizootic hemorrhagic disease virus (EHDV) circulation in France in 2023

Bluetongue (BT) and Epizootic Hemorrhagic Disease (EHD) are two notifiable animal diseases transmitted to ruminants by small hematophagous midges belonging to the Culicoides genus. The etiological agents, Bluetongue virus (BTV) and Epizootic hemorrhagic disease virus (EHDV), are both members of the Sedoreoviridae family and Orbivirus genus, which include double-stranded (ds) RNA segmented genomes (10 segments). By the end of the summer 2023, first's outbreaks of EHD were reported from the south west of France, concurrently with unexpectedly severe BT cases in Central France and Corsica. Within a few weeks, numerous BT and EHD outbreaks were recorded with significant sanitary and economic impact on cattle and sheep farms (no sanitary impact of EHD for sheep). Using a customized SISPA approach and the nanopore sequencing technology we successfully recovered genomic sequences from viral isolates and blood samples from infected animals from EHD and BT outbreaks. Three different viruses were responsible for these outbreaks: EHDV-8, BTV-8 and BTV-4. The EHDV-8 strain detected in France corresponded to the strain circulating in Tunisia, Sardinia and Spain since 2021 and 2022. A new BTV-8 strain of unknown origin, clearly different from the enzootic strain circulating in France since 2015, was responsible of the BT outbreaks in domestic ruminants in 2023 on both mainland France and Corsica. A second BTV, BTV-4, also involved in BT outbreaks in Corsica, corresponded to a BTV-4 strain occasionally detected on Corsica island since 2016, suggesting either a new introduction of this strain or a silent circulation on the field. The exceptional nature of orbivirus epizootics in France in 2023, including new introduction, emergence or incursions, raises numerous questions regarding BTV and EHDV dynamics and epidemiology and stresses out the need to identify factors involved in these emergences.

Culicoides Latreille (Diptera, Ceratopogonidae) of Colombia: records from the collection of insects of medical importance from National Institute of Health

Background

The collection of insects of medical importance from the Instituto Nacional de Salud, INS (Bogotá, Colombia: https://www.ins.gov.co/Paginas/Inicio.aspx), was started in 1934 with the aim of being an institutional and national repository of the biodiversity of insects involved in vector-borne diseases of importance in public health. Today, the entomological collection includes more than 7,500 specimens.The ceratopogonid insects are one group of Diptera that are represented in this collection. Within the Ceratopogonidae, the genus Culicoides Latreille, 1809 is relevant in public health because of the nuisance caused by their bites when they are presented in great abundance and because of their role as vectors of several agents (virus, protozoa and nematodes) that cause diseases to humans and to animals (Mellor et al. 2000, Mullen 2002). An overview of the Ceratopogonidae, represented in this collection, is presented here. A total of 801 individuals, mainly adults of the genus Culicoides (90%) are represented. The collection is the result of the effort of several researchers of the Group of Entomology at INS. These researchers collected ceratopogonids when they went to different transmission scenarios of vector-borne diseases in Colombia, with the purpose of making entomological characterisations including the processing, assembly and identification of the specimens in the laboratory.

New information

New information about the geographical distribution of 39 species of the genus Culicoides in Colombia. All data have been uploaded to GBIF and are publicly available there.

Large-Scale Cytochrome C Oxidase Subunit I Gene Data Analysis for the Development of a Multiplex Polymerase Chain Reaction Test Capable of Identifying Biting Midge Vector Species and Haplotypes (Diptera: Ceratopogonidae) of the Culicoides Subgenus Avaritia Fox, 1955

The emergence of culicoid-transmitted bluetongue and Schmallenberg viruses in several European countries demonstrated the ability of indigenous biting midge species to transmit pathogens. Entomologic research programs identified members of the Obsoletus Group (Culicoides subgenus Avaritia) as keyplayers in disease epidemiology in Europe. However, morphological identification of potential vectors is challenging due to the recent discovery of new genetic variants (haplotypes) of C. obsoletus sensu stricto (s.s.), forming distinct clades. In this study, 4422 GenBank entries of the mitochondrial cytochrome c oxidase subunit I (COI) gene of subgenus Avaritia members of the genus Culicoides were analyzed to develop a conventional multiplex PCR, capable of detecting all vector species and clades of the Western Palearctic in this subgenus. Numerous GenBank entries incorrectly assigned to a species were identified, analyzed and reassigned. The results suggest that the three C. obsoletus clades represent independent species, whereas C. montanus should rather be regarded as a genetic variant of C. obsoletus s.s. Based on these findings, specific primers were designed and validated with DNA material from field-caught biting midges which achieved very high diagnostic sensitivity (100%) when compared to an established reference PCR (82.6%).

First molecular evidence of potential Culicoides vectors implicated in bluetongue virus transmission in Morocco

BACKGROUND

Bluetongue is a non-contagious viral disease that affects both domestic and wild ruminants. It is transmitted primarily by small hematophagous Diptera belonging to the genus Culicoides (Diptera: Ceratopogonidae). The current study represents the first molecular investigation into the potential role of Culicoides imicola, Culicoides paolae, Culicoides newsteadi, Culicoides spp., and Culicoides circumscriptus as bluetongue virus (BTV) vectors in Morocco. Additionally, the study aimed to evaluate the vectorial activity of midges during the survey seasons.

METHODS

Parous females of these species were captured from several regions of Morocco (6 out of 12) from 2018 to 2021 using Onderstepoort Veterinary Institute (OVI) traps. A total of 2003 parous female specimens were grouped into 55 batches. The midge body of each batch was dissected into three regions (head, thorax, and abdomen), and these regions were analyzed separately using reverse transcription quantitative polymerase chain reaction (RT-qPCR).

RESULTS

BTV RNA was detected in 45 out of the 55 batches tested, indicating a positivity rate of 81.8%. The RT-qPCR-positive pools of the studied Culicoides species exhibited high levels of BTV positivity in each body part (head, thorax, and abdomen), confirming the successful replication of the virus within midge bodies. The BTV circulation was substantial across all three survey seasons (spring, summer, and autumn). High infection rates, calculated using the minimum infection rate (MIR) and maximum likelihood estimation (MLE), were observed during the collection seasons, particularly in autumn and spring, and for all investigated Culicoides species, most notably for C. imicola and C. newsteadi. These increased infection rates underscore the significant risk of Culicoides transmitting the BTV in Morocco.

CONCLUSIONS

The detection of BTV positivity in Culicoides spp. (lacking wing spots that allow their differentiation according to morphological identification keys) suggested that other Culicoides species are competent for BTV transmission in Morocco. The study results indicated, for the first time at the molecular level, that C. imicola and C. newsteadi are the primary potential vectors of BTV in Morocco and that C. paolae and C. circumscriptus are strongly implicated in the propagation of bluetongue at the national level.

Systematic review of hematophagous arthropods present in cattle in France

The arrival of pathogens, whether zoonotic or not, can have a lasting effect on commercial livestock farms, with dramatic health, social and economic consequences. However, available data concerning the arthropod vectors present and circulating on livestock farms in France are still very imprecise, fragmentary, and scattered. In this context, we conducted a systematic review of the hematophagous arthropod species recorded on different types of cattle farms in mainland France (including Corsica). The used vector "groups" studied were biting flies, biting midges, black flies, fleas, horse flies, lice, louse flies, mosquitoes, sand flies, and ticks. A large number of documents were selected (N = 9,225), read (N = 1,047) and analyzed (N = 290), allowing us to provide distribution and abundance maps of different species of medical and veterinary interest according to literature data. Despite the large number of documents collected and analyzed, there are few data provided on cattle farm characteristics. Moreover, data on all arthropod groups lack numerical detail and are based on limited data in time and/or space. Therefore, they are not generalizable nor comparable. There is still little information on many vectors (and their pathogens) and still many unknowns for most studied groups. It appears necessary to provide new, updated and standardized data, collected in different geographical and climatological areas. Finally, this work highlights the lack of entomologists, funding, training and government support, leading to an increased risk of uncontrolled disease emergence in cattle herds.

Effect of Exercise in a Vector-Protected Arena for Preventing African Horse Sickness Transmission on Physiological, Biochemical, and Behavioral Variables of Horses

During an African horse sickness (AHS) outbreak, horses were able to exercise daily in a net-covered arena, yet the physiological responses to exercise in a netted arena was unknown. In a cross-over study design, eight horses performed a 39-minute aerobic exercise in conventional (CA) and vector-protected arenas (VPA). Horses were slower in some gaits and covered less distance in the VPA arena (P < .01). Cortisol release, hematology, and heart rate variability (HRV) were also examined. An interaction between the riding arena and time was observed in hematocrit (P = .0013), hemoglobin (P = .0012), and red blood cell count (P = .0027) and HRV variables, including mean beat-to-beat (RR) intervals (P < .0001), mean heart rate (P < .0001), sympathetic nervous system (SNS) index (P = .0038) and parasympathetic nervous system (PNS) index (P < .0001). Cortisol concentrations increased during exercise and 30 minutes postexercise in both arenas. Hematocrit, hemoglobin, and red blood cell count increased immediately postexercise in horses in VPA while remaining high from immediate post-exercise to 60 minutes postexercise in horses in CA. HRV decreased during exercise and was not different between horses in both arenas, but a higher RR interval and PNS index, corresponding to lower heart rate and SNS index, were detected during 30 to 60 minutes postexercise in horses in the VPA compared to the CA. Riding horses in different arenas impacted hematological and HRV variables. The greater RR intervals and PNS index, coinciding with the lower SNS index and heart rate, indicated parasympathetic dominance post-exercise in horses in VPA compared to CA.

Biting Midges (Diptera: Ceratopogonidae) as Vectors of Viruses

Biting midges of the genus Culicoides occur almost globally and can regionally and seasonally reach high abundances. Most species are hematophagous, feeding on all groups of vertebrates, including humans. In addition to being nuisance pests, they are able to transmit disease agents, with some viruses causing high morbidity and/or mortality in ruminants, horses and humans. Despite their impact on animal husbandry, public health and tourism, knowledge on the biology and ecology of culicoid biting midges and their interactions with ingested pathogens or symbiotic microorganisms is limited. Research is challenging due to unknown larval habitats, the insects' tiny size, the inability to establish and breed most species in the laboratory and the laborious maintenance of colonies of the few species that can be reared in the laboratory. Consequently, the natural transmission of pathogens has experimentally been demonstrated for few species while, for others, only indirect evidence of vector potential exists. Most experimental data are available for Culicoides sonorensis and C. nubeculosus, the only species kept in western-world insectaries. This contribution gives an overview on important biting midge vectors, transmitted viruses, culicoid-borne viral diseases and their epidemiologies and summarizes the little knowledge on interactions between biting midges, their microflora and culicoid-borne arboviruses.

Wing morphometrics of biting midges (Diptera: Culicoides) of veterinary importance in Madagascar

Biting midges are vectors of arboviruses such as bluetongue virus, bovine ephemeral fever virus, Akabane virus, African horse sickness virus, epizootic haemorrhagic disease virus and Schmallenberg virus. Fast and accurate identification of biting midges is crucial in the study of Culicoides-borne diseases. Morphological identification of biting midges has revealed the presence of cryptic species. A total of 20 species are reported in Madagascar. In this study, we assessed wing morphometric analysis for identification of seven species namely C. dubitatus Kremer, Rebholtz-Hirtzel and Delécolle, C. enderleini Cornet and Brunhes, C. kibatiensis Goetghebuer, C. miombo Meiswinkel, C. moreli Clastrier, C. nevilli Cornet and Brunhes, and C. zuluensis de Meillon. Culicoides enderleini, C. miombo, C. moreli, C. nevilli and C. zuluensis are vectors diseases. A molecular approach, based on the cytochrome oxidase I gene (Cox1), was used for species delimitation. The molecular analysis presented seven different clades grouped two-by-two according to morphological characters. A total of 179 wing images were digitised. We found morphometric variation among seven species based on 11 landmarks and two outlines. Wing shape variation plots showed that species overlapped with species belonging to the same group. The cross-validation revealed a relatively high percentage of correct classification in most species, ranging from 91.3% to 100% for landmarks; 60% to 82.6% for outlines-1 and 77.1% to 91.3% for outlines-2. Our study suggests that wing geometric morphometric analysis is a robust tool for reliable "Moka Fohy" identification in Madagascar. This inexpensive and simple method is a precise supplement to morphological identification, with reaches the accuracy of Cox1 barcoding.

An updated catalogue of biting midges of the genus Culicoides Latreille, 1809 (Diptera, Ceratopogonidae) of Mexico and their known distribution by state

An updated catalogue of Culicoides of Mexico is presented. It includes 86 species with their regional distribution and corresponding record references, known immature stages and associated pathogens. In addition, a taxonomic key for subgenera and species groups for Mexico is presented and an index of species by state is included.

DNA Barcoding of Culicoides Latreille (Diptera: Ceratopogonidae) From Thailand Reveals Taxonomic Inconsistencies and Novel Diversity Among Reported Sequences

Recent focus on Culicoides species diversity in Thailand was prompted by a need to identify vectors responsible for the transmission of African Horse Sickness in that country. To assist rapid genetic identification of species, we sampled mitochondrial cytochrome c oxidase subunit I (COI) DNA barcodes (N = 78) from 40 species of Culicoides biting midge from Thailand, including 17 species for which DNA barcodes were previously unavailable. The DNA barcodes were assigned to 39 Barcode Identification Numbers (BINs) representing terminal genetic clusters at the Barcode of Life Data systems (BOLD). BINs assisted with comparisons to published conspecific DNA barcodes and allowed partial barcodes obtained from seven specimens to be associated with BINs by their similarity. Some taxonomic issues were revealed and attributed to the possible misidentification of earlier reported specimens as well as a potential synonymy of C. elbeli Wirth & Hubert and C. menglaensis Chu & Liu. Comparison with published BINs also revealed genetic evidence of divergent population processes and or potentially cryptic species in 16 described taxa, flagged by their high levels of COI sequence difference among conspecifics. We recommend the BOLD BIN system to researchers preparing DNA barcodes of vouchered species for public release. This will alert them to taxonomic incongruencies between their records and publicly released DNA barcodes, and also flag genetically deep and potentially novel diversity in described species.

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.

DNA Barcoding of genus Culicoides biting midges (Diptera: Ceratopogonidae) in the Brazilian Amazon

Culicoides biting midges are capable to transmit Oropouche virus, Bluetongue virus and Mansonella spp. This study aimed to assess the utility of DNA barcode as an alternative method in the Culicoides species identification. The study was conducted in Jamari National Forest. Biting midges were collected using HP light traps during four months, February, April, August and October, 2018. Insects were morphologically identified to the species level, and rest of the body were subjected to DNA extraction and PCR targeting a fragment of the cytochrome c oxidase subunit I (COI) gene, which were analyzed and deposited in GenBank. A phylogenetic gene tree was reconstructed using RAxML software, and the sequences were assigned at Molecular Operational Taxonomic Unit (MOTU) level by species delimitation algorithms. According to morphological approach, 18 species of 2 subgenera and 7 species groups were identified. A total of 191 new COI barcodes from 18 species were generated. Of these, fifteen species have been deposited for the first time in all datasets in the world. These sequences allowed the correct identification of 188 and 187 specimens according to the BM and BCM criteria, respectively. The intraspecific genetic distances ranged from 0 to 16.5%, while the interspecific ones ranged from 2.1 to 27.1%. The nominal species Culicoides glabellus and C. tetrathyris splitted into three and two MOTUs, respectively, except for mPTP, indicating a cryptic diversity in these species. Also, sequences of C. pseudodiabolicus formed two MOTUs using all algorithms, except for PTP and ABGD, suggesting the existence of two potential species. In contrast, some barcodes of C. quasiparaensis and C. paraensis merged into a single MOTU, which can be explained by the complex characteristics of the paraensis group, since these species have similar morphological characters. Here, we provided the first COI barcodes for biting midges in Rondônia and Brazil, and demonstrates that these are sufficient to discriminate between some species.

A Review of the Vector Status of North American Culicoides (Diptera: Ceratopogonidae) for Bluetongue Virus, Epizootic Hemorrhagic Disease Virus, and Other Arboviruses of Concern

Purpose of Review

Culicoides biting midges transmit several pathogens of veterinary importance in North America, but the vector status of many midge species is unresolved. Additionally, the available evidence of vector competence in these species is scattered and variable. The purpose of this review is to summarize current knowledge on confirmed and putative North American Culicoides arbovirus vectors.

Recent Findings

While the vector status of Culicoides sonorensis (EHDV, BTV, VSV) and Culicoides insignis (BTV) are well established, several other potential vector species have been recently identified. Frequently, these species are implicated based primarily on host-feeding, abundance, and/or detection of arboviruses from field-collected insects, and often lack laboratory infection and transmission data necessary to fully confirm their vector status. Recent genetic studies have also indicated that some wide-ranging species likely represent several cryptic species, further complicating our understanding of their vector status.

Summary

In most cases, laboratory evidence needed to fully understand the vector status of the putative Culicoides vectors is absent; however, it appears that several species are likely contributing to the transmission of arboviruses in North America.

Occurrence of Biting Midges (Diptera: Culicoides) on Dairy Farms in Eastern Slovakia in Relation to Abiotic Factors

Within the scope of our research, we have performed 59 trapping sessions and collected 15,756 biting midges from 20 species at four farms (Kluknava, Ostrov, Turňa nad Bodovou and Zemplínska Teplica), The most frequent types of captured insects were representatives of the Avaritia subgenus, C. obsoletus/C. scoticus, representing on average 85.1 % (13,295 individuals) of the fauna of the biting midges, with the exception of the farm in Ostrov where this group represented only 41.7 % of the fauna. At this particular farm, the most frequently trapped insects belonged to the Culicoides subgenus (54.1 %), in particular the C. bysta, C. lupicaris, C. newsteadi, C. Pulicaris and C. Punctatus species. During the trapping sessions, we monitored factors affecting the number of trapped biting midges, such as the temperature, relative air humidity and airflow rate: the air temperature during the trapping of the biting midges ranged from 9.8 to 26.2 °C; the relative air humidity ranged from 35.1 to 100 %; and the air flow rate ranged from no wind to a wind velocity of 8.2 m.s-1. However, in the final evaluation, we failed to observe a statistically significant correlation between the air flow and the number of trapped biting midges. The largest amounts of biting midges were trapped at temperatures ranging from 15.8 to 24.6 °C and at a relative air humidity ranging from 54.2 % to 68.6 %. While monitoring the seasonal dynamics of the physiological conditions of biting midge females at the selected farms, we confirmed that during the period from June to August, the most frequently trapped females were parous (50.1 %; 7,826 individuals). In addition, nulliparous females comprised 43.8 % (6,842 individuals) and were continuously trapped throughout the season (April— November).

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.

DNA barcode identification and molecular detection of bluetongue virus in Culicoides biting midges (Diptera: Ceratopogonidae) from western Thailand

Biting midges of the genus Culicoides Latreille are biological vectors of bluetongue virus (BTV), a member of family Reoviridae, genus Orbivirus. About 30 species of Culicoides have been identified as competent BTV vectors worldwide. Even though high seroprevalence of BTV has been reported among livestock ruminants from western Thailand, the Culicoides species which contribute to BTV transmission remain unclear. In the present study, Culicoides were collected from eight sampling sites, located in two BTV prevalent provinces in western Thailand. Adult Culicoides were identified using wing morphology and cytochrome c oxidase subunit I (COI) mtDNA molecular marker. A total of 9,677 Culicoides specimens belonging to 7 subgenera, 3 species groups, and 23 species were identified. After comparing sequencing results with available data from GenBank, COI sequences of five species were reported for the first time from Thailand. The most abundant potential BTV vector species collected were C. peregrinus, followed by C. orientalis, C. imicola, C. oxystoma, and C. fulvus. Out of 72 Culicoides pools, 9 pools (4 from C. orientalis, 2 from C. imicola, 2 from C. oxystoma, and 1 from C. fulvus) were positive by BTV RT-PCR analyses. These results are new to Culicoides BTV vector knowledge in Thailand and will contribute to further BTV studies in this particular region.

Summer seasonal prevalence of Culicoides species from pre-alpine areas in Switzerland

Biting midges (Diptera: Ceratopogonidae) are arthropods of veterinary importance since they can transmit pathogens and cause severe allergic dermatitis in horses. Very little is known about the species at higher altitudes and their seasonal dynamics. In this work, adult Culicoides were collected with Onderstepoort UV-light suction traps (OVI) from June to September 2016 at two areas situated at around 1600 m asl (pre-alpine area I, 2 farms) and 2030 m asl (pre-alpine area II, 1 farm) in the Canton of Grisons (south-east Switzerland). Overall, 17 049 Culicoides were collected, including 871 parous females. A total of 50 individuals/trap/night (n = 1050) were identified to species (17 species) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) or by polymerase chain reaction (PCR) and sequencing. The remaining 15 128 Culicoides were classified to species groups' level. Culicoides obsoletus (Meigen, 1818), a multivoltine species, was mainly present at 1600 m asl, whereas at high altitudes (2030 m asl), C. grisescens Edwards, 1939 I&II were the most abundant species. In particular, C. grisescens II, which seems to be univoltine, occurred later in the season but significantly increasing over time. Species diversity was higher at pre-alpine I area (n = 16 species) compared to pre-alpine II (n = 10 species).

Molecular Detection of Leishmania (L.) mexicana (Kinetoplastida: Trypanostomatidae) DNA in Culicoides furens (Diptera: Ceratopogonidae) from an Area with Autochthonous Canine Leishmaniasis in Northwestern Mexico

PURPOSE

Mexico is considered endemic for Leishmania; recent reports indicate autochthonous human and canine leishmaniasis caused by Leishmania mexicana in Sinaloa state. Lutzomyia sand fly are the primary vector of the parasite, although no records of phlebotomine vectors of Leishmania exist from Sinaloa. Other hematophagous dipterans, like Culicoides, could represent possible vectors of Leishmania in absence of phlebotomines. The known distribution of Culicoides includes the southern portion of Sinaloa state, in northwestern Mexico, with records of Culicoides furens. However, no studies have demonstrated the presence of Leishmania in C. furens or its possible participation in the parasite's life cycle in Mexico. This study, therefore, sought to detect DNA of Leishmania in C. furens captured in an endemic area of autochthonous canine leishmaniasis in northwestern Mexico.

METHODS

Culicoides were captured with CDC light traps, identified morphologically, and organized in pools. DNA was extracted, and used to amplify the ribosomal ITS1 region of Leishmania. PCR products were digested with HaeIII endonuclease; the banding patterns obtained were compared to reference strains.

RESULTS

Leishmania mexicana DNA was detected in five out of nine pools (55%) of female C. furens.

CONCLUSION

This study offers the first evidence of L. mexicana DNA in C. furens, in an endemic area of canine leishmaniasis in northwestern Mexico, where no evidence exists of the presence of phlebotomine sand fly.

Beyond taxonomy: species complexes in New World phlebotomine sand flies

A species complex (= species group, species series) is an assemblage of species, which are related morphologically and phylogenetically. Recent research has revealed several arthropod vector species that were believed to be a single nominal species actually representing a group of closely related species, which are sometimes morphologically indistinguishable at one or more developmental stages. In some instances, differences in terms of vector competence, capacity, or both have been recorded. It highlights the importance of detecting and studying species complexes to improve our understanding of pathogen transmission patterns, which may be vectored more or less efficiently by different species within the complex. Considering more than 540 species, about one-third of the phlebotomine sand flies in the New World present males and/or females morphologically indistinguishable to one or more species. Remarkably, several of these species may act in transmission of pathogenic agents. In this article, we review recent research on species complexes in phlebotomine sand flies from the Americas. Possible practical implications of recently acquired knowledge and future research needs are also discussed.

Integrative taxonomy uncovers a new Culicoides (Diptera: Ceratopogonidae) biting midge species from Thailand

Fully understanding biodiversity often requires an integrated approach especially for small insects because species diagnostic morphological characters are limited. In this study, morphological characters and DNA barcodes were used to examine previously recognized genetically divergent lineages detected in the biting midge, Culicoides arakawae (Arakawa), from Thailand. Morphological examinations revealed that specimens belonging to one lineage are morphologically different from C. arakawae in shape of the paramere in males, and in the leg color pattern of both sexes. Therefore, a formal description is provided for this new species, Culicoides mahasarakhamense sp. nov. Based on morphological characters including a large and shallow palpal pit, one sac like spermatheca and male with parameres bent at base with large basal knob, the new species was assigned into the subgenus Meijerehelea Wirth and Hubert. Morphological differentiation including wing pattern and shape of spermatheca of the new species are discussed and compared with other members of this subgenus. Mitochondrial cytochrome c oxidase I sequence analysis indicated that this new species is different from other members of the subgenus Meijerehelea with minimum interspecific genetic divergence of 3.92%. Automatic Barcode Gap Discovery species delimitation analysis also supported the recognition of a new species. Phylogenetic analyses revealed that the new species is closely related to C. arakawae, consistent with morphological similarity of these species. Results of this study highlight the necessity of using integrated approach for Culicoides taxonomy.

A study of the composition of the Obsoletus complex and genetic diversity of Culicoides obsoletus populations in Spain

Background

The Culicoides obsoletus species complex (henceforth ‘Obsoletus complex’) is implicated in the transmission of several arboviruses that can cause severe disease in livestock, such as bluetongue, African horse sickness, epizootic hemorrhagic disease and Schmallenberg disease. Thus, this study aimed to increase our knowledge of the composition and genetic diversity of the Obsoletus complex by partial sequencing of the cytochrome c oxidase I (cox1) gene in poorly studied areas of Spain.

Methods

A study of C. obsoletus populations was carried out using a single-tube multiplex polymerase chain reaction (PCR) assay that was designed to differentiate the Obsoletus complex sibling species Culicoides obsoletus and Culicoides scoticus, based on the partial amplification of the cox1 gene, as well as cox1 georeferenced sequences from Spain available at GenBank. We sampled 117 insects of the Obsoletus complex from six locations and used a total of 238 sequences of C. obsoletus (ss) individuals (sampled here, and from GenBank) from 14 sites in mainland Spain, the Balearic Islands and the Canary Islands for genetic diversity and phylogenetic analyses.

Results

We identified 90 C. obsoletus (ss), 19 Culicoides scoticus and five Culicoides montanus midges from the six collection sites sampled, and found that the genetic diversity of C. obsoletus (ss) were higher in mainland Spain than in the Canary Islands. The multiplex PCR had limitations in terms of specificity, and no cryptic species within the Obsoletus complex were identified.

Conclusions

Within the Obsoletus complex, C. obsoletus (ss) was the predominant species in the analyzed sites of mainland Spain. Information about the species composition of the Obsoletus complex could be of relevance for future epidemiological studies when specific aspects of the vector competence and capacity of each species have been identified. Our results indicate that the intraspecific divergence is higher in C. obsoletus (ss) northern populations, and demonstrate the isolation of C. obsoletus (ss) populations of the Canary Islands.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04841-z.

Validation of an Effective Protocol for Culicoides Latreille (Diptera: Ceratopogonidae) Detection Using eDNA Metabarcoding

Simple Summary

All organisms shed genetic material into the environment, which is known as environmental DNA. Current molecular technologies allow for sequencing molecular markers in complex environmental samples. The use of these methods permits an effective identification and monitoring of flighted insects such as Culicoides species. These biting midges are agricultural pests of significant economic concern. This study identified Culicoides species using a novel molecular-based approach for this group and compared these results to morphological identifications of the specimens collected. There were forty-two Culicoides specimens collected in total, using a saturated salt solution as a collection fluid. Molecular identification detected four species. Using morphological identification, we identified two out of these four taxonomic ranks at the species level and one at the subgenus level. The inconsistency in identifying Culicoides specimens to the species level indicates the need for curated DNA reference libraries for molecular-based identification. The saturated salt solution used in the traps preserved the morphological characteristics and the organisms’ environmental DNA, which is an essential contribution of this study.

Abstract

eDNA metabarcoding is an effective molecular-based identification method for the biosurveillance of flighted insects. An eDNA surveillance approach maintains specimens for secondary morphological identification useful for regulatory applications. This study identified Culicoides species using eDNA metabarcoding and compared these results to morphological identifications of trapped specimens. Insects were collected using ultraviolet (UV) lighted fan traps containing a saturated salt (NaCl) solution from two locations in Guelph, Ontario, Canada. There were forty-two Culicoides specimens collected in total. Molecular identification detected four species, C. biguttatus, C. stellifer, C. obsoletus, and C. mulrennani. Using morphological identification, two out of these four taxonomic ranks were confirmed at the species level (C. biguttatus and C. stellifer) and one was confirmed at the subgenus level (Avaritia [C. obsoletus]). No molecular detection of Culicoides species occurred in traps with an abundance of less than three individuals per taxon. The inconsistency in identifying Culicoides specimens to the species level punctuates the need for curated DNA reference libraries for Culicoides. In conclusion, the saturated salt (NaCl) solution preserved the Culicoides’ morphological characteristics and the eDNA.

Culicoides insignis Lutz, 1913 (Diptera: Ceratopogonidae) Biting Midges in Northeast of Brazil

Simple Summary

Culicoides genus insects are spread throughout the world, and some species are vectors of important human and animal diseases. Genetic identification, as well as the local occurrence of these insects, are fundamental to the development of risk profiles and entomological surveillance of transmitted diseases. We investigated the Culicoides occurrence in Alagoas State, northeastern Brazil. Midges were captured with light traps, being morphologic and genetic identified. After PCR analysis and GenBank database comparison, it was confirmed that the captured midges belong to Culicoides insignis. This was the first formal report of Culicoides insignis occurrence in Alagoas State, northeastern Brazil.

Abstract

The species of the Culicoides genus are hematophagous, and some of them are vectors of important human and animal diseases. This group of insects is distributed worldwide, varying according to local species. Knowledge of the geographic distribution of specific species is crucial for the development and implementation of control strategies. The aim of this work was to investigate the occurrence of Culicoides in the state of Alagoas in northeast Brazil. Midges were captured with CDC light traps, and their identification and morphological analyses were performed by the Ceratopogonidae Collection of the Oswaldo Cruz Foundation (FIOCRUZ/CCER) in Rio de Janeiro, Brazil. Morphological analyses were performed using the key to Culicoides from the guttatus group and comparison with other deposited specimens. DNA sequencing, genetic analysis and comparison with sequences in the Genbank database, confirmed the identification of the flies as Culicoides insignis. This was the first formal report of C. insignis being found in Alagoas.

Comprehensive characterisation of Culicoides clastrieri and C. festivipennis (Diptera: Ceratopogonidae) according to morphological and morphometric characters using a multivariate approach and DNA barcode

Biting midges are widespread around the world and play an essential role in the epidemiology of over 100 veterinary and medical diseases. For taxonomists, it is difficult to correctly identify species because of affinities among cryptic species and species complexes. In this study, species boundaries were examined for C. clastrieri and C. festivipennis and compared with six other Culicoides species. The classifiers are partial least squares discriminant analysis (PLS-DA) and sparse partial least squares discriminant analysis (sPLS-DA).The performance of the proposed method was evaluated using four models: (i) geometric morphometrics applied to wings; (ii) morphological wing characters, (iii) "Full wing" (landmarks and morphological characters) and (iv)  "Full model" (morphological characters-wing, head, abdomen, legs-and wing landmarks). Double cross-validation procedures were used to validate the predictive ability of PLS-DA and sPLS-DA models. The AUC (area under the ROC curve) and the balanced error rate showed that the sPLS-DA model performs better than the PLS-DA model. Our final sPLS-DA analysis on the full wing and full model, with nine and seven components respectively, managed to perfectly classify our specimens. The C. clastrieri and C. festivipennis sequences, containing both COI and 28S genes, revealed our markers' weak discrimination power, with an intraspecific and interspecific divergence of 0.4% and 0.1% respectively. Moreover, C. clastrieri and C. festivipennis are grouped in the same clade. The morphology and wing patterns of C. clastrieri and C. festivipennis can be used to clearly distinguish them. Our study confirms C. clastrieri and C. festivipennis as two distinct species. Our results show that caution should be applied when relying solely on DNA barcodes for species identification or discovery.

Environmental Drivers of Adult Seasonality and Abundance of Biting Midges Culicoides (Diptera: Ceratopogonidae), Bluetongue Vector Species in Spain

Bluetongue is a viral disease affecting wild and domestic ruminants transmitted by several species of biting midges Culicoides Latreille. The phenology of these insects were analyzed in relation to potential environmental drivers. Data from 329 sites in Spain were analyzed using Bayesian Generalized Linear Mixed Model (GLMM) approaches. The effects of environmental factors on adult female seasonality were contrasted. Obsoletus complex species (Diptera: Ceratopogonidae) were the most prevalent across sites, followed by Culicoides newsteadi Austen (Diptera: Ceratopogonidae). Activity of female Obsoletus complex species was longest in sites at low elevation, with warmer spring average temperatures and precipitation, as well as in sites with high abundance of cattle. The length of the Culicoides imicola Kieffer (Diptera: Ceratopogonidae) female adult season was also longest in sites at low elevation with higher coverage of broad-leaved vegetation. Long adult seasons of C. newsteadi were found in sites with warmer autumns and higher precipitation, high abundance of sheep. Culicoides pulicaris (Linnaeus) (Diptera: Ceratopogonidae) had longer adult periods in sites with a greater number of accumulated degree days over 10°C during winter. These results demonstrate the eco-climatic and seasonal differences among these four taxa in Spain, which may contribute to determining sites with suitable environmental circumstances for each particular species to inform assessments of the risk of Bluetongue virus outbreaks in this region.

An approach to automatic classification of Culicoides species by learning the wing morphology

Fast and accurate identification of biting midges is crucial in the study of Culicoides-borne diseases. In this work, we propose a two-stage method for automatically analyzing Culicoides (Diptera: Ceratopogonidae) species. First, an image preprocessing task composed of median and Wiener filters followed by equalization and morphological operations is used to improve the quality of the wing image in order to allow an adequate segmentation of particles of interest. Then, the segmentation of the zones of interest inside the biting midge wing is made using the watershed transform. The proposed method is able to produce optimal feature vectors that help to identify Culicoides species. A database containing wing images of C. obsoletus, C. pusillus, C. foxi, and C. insignis species was used to test its performance. Feature relevance analysis indicated that the mean of hydraulic radius and eccentricity were relevant for the decision boundary between C. obsoletus and C. pusillus species. In contrast, the number of particles and the mean of the hydraulic radius was relevant for deciding between C. foxi and C. insignis species. Meanwhile, for distinguishing among the four species, the number of particles and zones, and the mean of circularity were the most relevant features. The linear discriminant analysis classifier was the best model for the three experimental classification scenarios previously described, achieving averaged areas under the receiver operating characteristic curve of 0.98, 0.90, and 0.96, respectively.

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.

Abundance, diversity and temporal activity of adult Culicoides spp. associated with cattle in West Bengal, India

Relative abundance, species composition and temporal activity of Culicoides midges were studied for a period of 2 years (2012-2014) using suction ultra violet light traps at two sites located in the agriculture heartland of West Bengal, India. Surveillance in close proximity to cattle recorded predominance of five species with C oxystoma and C. peregrinus as the most dominant species followed by C. fulvus, C. innoxius and C. anophelis. The temporal activity of midges was investigated for seven consecutive nights at one site in August-September, 2012 and the predominant species was Culicoides oxystoma followed by Culicoides peregrinus. All of the species exhibited crepuscular activity with their flight activity increasing from dusk to dawn. Engorged adults constituted dominant age group in collections. Studies on population ecology of the adults midges are of considerable importance predicting for the epidemicity of midge-borne diseases in cattle.

Breeding Habitat Preferences of Major Culicoides Species (Diptera: Ceratopogonidae) in Germany

Biting midges of the genus Culicoides (Diptera, Ceratopognidae) are demonstrably or putatively involved in the transmission of both bluetongue (BTV) and Schmallenberg viruses (SBV) in Central Europe. Although these insects are ubiquitous in Europe, relatively little is known about their requirements in terms of breeding habitats and substrates. Culicoides species composition and relative abundance in potential breeding habitats were therefore studied at various locations in Northeastern Germany and one location in Western Germany by emergence trap collections. Forty-three potential breeding sites were analyzed in ten landscape structures, with 28,091 adult biting midges emerging from them. Among these, 2116 specimens belonged to the genus Culicoides. Species of the culicoid subgenus Avaritia were most abundant (70.6% of all specimens) and widespread (91.6% of all sites), while the subgenus Culicoides accounted for 15.6% of the specimens registered but emerged from 70.8% of all sites sampled. Culicoides species of other subgenera were collected in 75.0% of all studied sites, with a relative abundance of 8.7%. The results indicate that various types of dung, but probably also some landscape habitats, offer suitable substrates for the development of potential Culicoides vector species. Adaptations in dung management on farms and landscape design and use might therefore be appropriate approaches to reduce the risk of BTV or SBV transmission.

The tree that hides the forest: cryptic diversity and phylogenetic relationships in the Palaearctic vector Obsoletus/Scoticus Complex (Diptera: Ceratopogonidae) at the European level

Background

Culicoides obsoletus is an abundant and widely distributed Holarctic biting midge species, involved in the transmission of bluetongue virus (BTV) and Schmallenberg virus (SBV) to wild and domestic ruminants. Females of this vector species are often reported jointly with two morphologically very close species, C. scoticus and C. montanus, forming the Obsoletus/Scoticus Complex. Recently, cryptic diversity within C. obsoletus was reported in geographically distant sites. Clear delineation of species and characterization of genetic variability is mandatory to revise their taxonomic status and assess the vector role of each taxonomic entity. Our objectives were to characterize and map the cryptic diversity within the Obsoletus/Scoticus Complex.

Methods

Portion of the cox1 mitochondrial gene of 3763 individuals belonging to the Obsoletus/Scoticus Complex was sequenced. Populations from 20 countries along a Palaearctic Mediterranean transect covering Scandinavia to Canary islands (North to South) and Canary islands to Turkey (West to East) were included. Genetic diversity based on cox1 barcoding was supported by 16S rDNA mitochondrial gene sequences and a gene coding for ribosomal 28S rDNA. Species delimitation using a multi-marker methodology was used to revise the current taxonomic scheme of the Obsoletus/Scoticus Complex.

Results

Our analysis showed the existence of three phylogenetic clades (C. obsoletus clade O2, C. obsoletus clade dark and one not yet named and identified) within C. obsoletus. These analyses also revealed two intra-specific clades within C. scoticus and raised questions about the taxonomic status of C. montanus.

Conclusions

To our knowledge, our study provides the first genetic characterization of the Obsoletus/Scoticus Complex on a large geographical scale and allows a revision of the current taxonomic classification for an important group of vector species of livestock viruses in the Palaearctic region.

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.

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

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

A Mondrian matrix of seasonal patterns of Culicoides nulliparous and parous females at different latitudes in Spain

Insects from genus Culicoides (Diptera; Ceratopogonidae) transmit arboviruses such as Bluetongue virus (BTV); affecting wild and domestic ruminants. These insects are age graded for monitoring purposes in surveillance programs. Parous females (PF) are the only fraction of the entire population that could effectively transmit viruses in a subsequent blood meal. Data of the Spanish Entomosurveillance National Program from 2008 to 2010 were used to analyse the seasonal pattern of the nulliparous females (NF) and PF of the vector species Obsoletus complex, C. imicola, C. newsteadi and C. pulicaris. Latitude variation on the seasonal abundance patterns of PF was also analysed in trap sites spanning a North-South axis in mainland Spain. The weekly abundance of PF was always highest in summer. The peak of abundance mainly occurred between April and July except for C. imicola that was from September to November. The analysis of the latitudinal seasonal variation of PF in Spain showed that Northern provinces have absence of C. imicola while the Obsoletus species were more present in Northern areas. There were periods of the year were no individuals of any vector species were collected, which should be considered in order to calculate the Seasonally Vector-Free Period (SVFP). Culicoides newsteadi and C. pulicaris exhibited the highest population in Toledo, probably related to their inland preferences. These findings would be of interest for a better understanding of the periods of low and high risk of transmission of BTV in Spain.

Red deer (Cervus elaphus) Did Not Play the Role of Maintenance Host for Bluetongue Virus in France: The Burden of Proof by Long-Term Wildlife Monitoring and Culicoides Snapshots

Bluetongue virus (BTV) is a Culicoides-borne pathogen infecting both domestic and wild ruminants. In Europe, the Red Deer (Cervus elaphus) (RD) is considered a potential BTV reservoir, but persistent sylvatic cycle has not yet been demonstrated. In this paper, we explored the dynamics of BTV1 and BTV8 serotypes in the RD in France, and the potential role of that species in the re-emergence of BTV8 in livestock by 2015 (i.e., 5 years after the former last domestic cases). We performed 8 years of longitudinal monitoring (2008–2015) among 15 RD populations and 3065 individuals. We compared Culicoides communities and feeding habits within domestic and wild animal environments (51,380 samples). Culicoides diversity (>30 species) varied between them, but bridge-species able to feed on both wild and domestic hosts were abundant in both situations. Despite the presence of competent vectors in natural environments, BTV1 and BTV8 strains never spread in RD along the green corridors out of the domestic outbreak range. Decreasing antibody trends with no PCR results two years after the last domestic outbreak suggests that seropositive young RD were not recently infected but carried maternal antibodies. We conclude that RD did not play a role in spreading or maintaining BTV in France.

Update of the species checklist of Culicoides Latreille, 1809 biting midges (Diptera: Ceratopogonidae) of Morocco

Background

Investigations of Culicoides fauna, including inventories, were carried out in Morocco at different periods after the country had faced major bluetongue and African horse sickness outbreaks. However, no comprehensive reference publication has provided a clear overview of the Culicoides species diversity. This study reviewed available data on Culicoides biting midge species in Morocco from 1968 to 2015 (published and grey literature in French and English) in order to revise the current checklist, in light of state of the art taxonomic and systematic knowledge, and confirmed the checklist with morphological and molecular identifications of specimens collected from the region of Rabat.

Methods

Literature related to Culicoides collections in Morocco was collated. Authors were contacted to obtain raw data and additional information for the collections. Fresh Culicoides material was collected and examined from two sites around Rabat, the capital of Morocco. Each collected individual was examined and morphologically identified, if possible, to the species level. In addition, molecular identification was performed to separate closely related species, to confirm difficult morphological identifications and to confirm new species records.

Results

A total of 6121 individuals of Culicoides spp. were collected and analyzed and at least 17 species were identified: C. cataneii/C. gejgelensis, C. circumscriptus, C. fagineus, C. festivipennis, C. imicola, C. jumineri, C. kingi, C. longipennis, C. montanus, C. newsteadi, C. obsoletus, C. paolae, C. parotti, C. puncticollis, C. sahariensis, C. scoticus and C. subfagineus. Seven species were confirmed using phylogenetic analyses. Two new species records for Morocco are reported: C. paolae and C. subfagineus.

Conclusions

The Moroccan fauna of Culicoides now includes 54 valid species. Further work would certainly increase this total, as one of the clades we identified was not affiliated to any described and valid species.

Latitudinal diversity of biting midge species within the Obsoletus group across three habitats in Europe

Culicoides species from the Obsoletus group are important vectors of bluetongue and Schmallenberg virus. This group consists of several species that cannot easily be identified using morphological characteristics. Therefore, limited information is available about their distribution and habitat preferences. In this study, we aimed to elucidate the species composition of the Obsoletus group in three habitat types at climatically different latitudes across Europe. Traps were placed in three habitat types in three countries at different latitudes. After DNA extraction, biting midges were identified using PCR and gel electrophoresis. Extraction of DNA using Chelex proved to be a cost and time efficient method for species identification. A latitudinal effect on the relative abundance of species from the Obsoletus group was found. Species composition was unique for most country-habitat combinations. The majority of biting midges were either C. obsoletus s.s. or C. scoticus, and both species were found at all latitudes and habitats. Their wide distribution and their high abundance at livestock farms make these species likely candidates for rapid farm-to-farm transmission of pathogens throughout Europe. Our results emphasize the need to differentiate Obsoletus group species to better understand their ecology and contribution to pathogen transmission.

Culicoides Latreille in the sun: faunistic inventory of Culicoides species (Diptera: Ceratopogonidae) in Mayotte (Comoros Archipelago, Indian Ocean)

BACKGROUND

The south-west insular territories of the Indian Ocean have recently received attention concerning the diversity of arthropods of medical or veterinary interest. While a recent study highlighted the circulation of Culicoides-borne viruses, namely bluetongue and epizootic hemorrhagic disease, with clinical cases in Mayotte (comprising two islands, Petite-Terre and Grand-Terre), Comoros Archipelago, no data have been published concerning the species diversity of Culicoides present on the two islands.

RESULTS

A total of 194,734 biting midges were collected in 18 sites, covering two collection sessions (April and June) in Mayotte. Our study reports for the first time livestock-associated Culicoides species and recorded at least 17 described Afrotropical species and one undescribed species. The most abundant species during the April collection session were C. trifasciellus (84.1%), C. bolitinos (5.4%), C. enderleini (3.9%), C. leucostictus (3.3%) and C. rhizophorensis (2.1%). All other species including C. imicola represented less than 1% of the total collection. Abundance ranged between 126-78,842 females with a mean and median abundance of 14,338 and 5111 individuals/night/site, respectively. During the June collection, the abundance per night was low, ranging between 6-475 individuals. Despite low abundance, C. trifasciellus and C. bolitinos were still the most abundant species. Culicoides sp. #50 is recorded for the first time outside South Africa.

CONCLUSIONS

Our study reports for the first time the Culicoides species list for Mayotte, Comoros Archipelago, Indian Ocean. The low abundance and rare occurrence of C. imicola, which is usually considered the most abundant species in the Afrotropical region, is unexpected. The most abundant and frequent species is C. trifasciellus, which is not considered as a vector species so far, but its role needs further investigation. Further work is needed to describe Culicoides sp. #50 and to carry on faunistic investigations on the other islands of the archipelago as well as in neighboring countries.

Genetic diversity of Culicoides species within the Pulicaris complex (Diptera: Ceratopogonidae) in Turkey inferred from mitochondrial COI gene sequences

Identification of Culicoides (Diptera: Ceratopogonidae) biting midges to species has become important due to their potential role in the transmission of arboviruses such as bluetongue virus, bovine ephemeral fever virus, Akabane virus, African horse sickness virus, epizootic haemorrhagic disease virus and Schmallenberg virus. In several studies, molecular tools, used for the identification of biting midges, revealed the presence of cryptic and undescribed species especially within Pulicaris complex. The presence of cryptic species within species complexes raise questions about their role in viral disease transmission as there are apparent differences in the vectorial capacity between closely related species. In this study, we analyzed the mitochondrial DNA cytochrome oxidase I (COI) gene sequences of species within the Pulicaris complex present in Turkey and determined their phylogenetic relationships. Twenty-one haplotypes within the already described species C. pulicaris P1, C. lupicaris, C. lupicaris L2, C. newsteadi, C. newsteadi N1, C. punctatus, C. fagineus F2 and C. flavipulicaris were determined from the study areas. The molecular analysis revealed further two haplotypes belonging to new non-described cryptic species named as C. lupicaris L3 and Culicoides WBS corresponding to C. lupicaris and Fagineus complex which diverged by 17.9% to 25.7% and 18.7% to 31.8%, respectively from other species in the subgenus Culicoides. Genetic divergence within species was <2.0% and phylogenetic analyses of the COI dataset revealed 22 different monophyletic separate clades within two major cluster. The results of this study emphasize the applicability of COI sequences as a diagnostic marker for differentiating Culicoides species and revealing cryptic species.

Reproducibility and relevance in insect-arbovirus infection studies

Experimental infections of insects with arboviruses are performed to achieve a variety of objectives but principally to draw inferences about the potential role of field populations in transmission or to explore the molecular basis of vector-pathogen interactions. The design of such studies determines both their reproducibility and the extent to which their results can be extrapolated to natural environments, and is constrained by the resources available. We discuss recent findings regarding the effects of nutrition, the microbiome, co-infecting agents and feeding methods on the outcome of such experiments, and identify resource-efficient ways to increase their relevance and reproducibility, including the development of community standards for reporting such studies and better standards for cell line and colony authentication.

Community analysis of the abundance and diversity of biting midge species (Diptera: Ceratopogonidae) in three European countries at different latitudes

BACKGROUND

The outbreaks of bluetongue and Schmallenberg disease in Europe have increased efforts to understand the ecology of Culicoides biting midges and their role in pathogen transmission. However, most studies have focused on a specific habitat, region, or country. To facilitate wider comparisons, and to obtain a better understanding of the spread of disease through Europe, the present study focused on monitoring biting midge species diversity in three different habitat types and three countries across Europe.

METHODS

Biting midges were trapped using Onderstepoort Veterinary Institute light traps at a total of 27 locations in Sweden, the Netherlands and Italy, comprising farm, peri-urban and wetland habitats. From July 2014 to June 2015 all locations were sampled monthly, except for during the winter months. Trapped midges were counted and identified morphologically. Indices on species richness, evenness and diversity were calculated. Community compositions were analysed using non-metric multidimensional scaling (NMDS) techniques.

RESULTS

A total of 50,085 female midges were trapped during 442 collection nights. More than 88% of these belonged to the Obsoletus group. The highest midge diversity was found in Sweden, while species richness was highest in the Netherlands, and most specimens were trapped in Italy. For habitats within countries, diversity of the trapped midges was lowest for farms in all countries. Differences in biting midge species communities were more distinct across the three countries than the three habitat types.

CONCLUSIONS

A core midge community could be identified, in which the Obsoletus group was the most abundant. Variations in vector communities across countries imply different patterns of disease spread throughout Europe. How specific species and their associated communities affect disease risk is still unclear. Our results emphasize the importance of midge diversity data at community level, how this differs across large geographic range within Europe, and its implications on assessing risks of midge-borne disease outbreaks.

Spatial and temporal variation in the abundance of Culicoides biting midges (Diptera: Ceratopogonidae) in nine European countries

BACKGROUND

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are vectors of bluetongue virus (BTV), African horse sickness virus and Schmallenberg virus (SBV). Outbreaks of both BTV and SBV have affected large parts of Europe. The spread of these diseases depends largely on vector distribution and abundance. The aim of this analysis was to identify and quantify major spatial patterns and temporal trends in the distribution and seasonal variation of observed Culicoides abundance in nine countries in Europe.

METHODS

We gathered existing Culicoides data from Spain, France, Germany, Switzerland, Austria, Denmark, Sweden, Norway and Poland. In total, 31,429 Culicoides trap collections were available from 904 ruminant farms across these countries between 2007 and 2013.

RESULTS

The Obsoletus ensemble was distributed widely in Europe and accounted for 83% of all 8,842,998 Culicoides specimens in the dataset, with the highest mean monthly abundance recorded in France, Germany and southern Norway. The Pulicaris ensemble accounted for only 12% of the specimens and had a relatively southerly and easterly spatial distribution compared to the Obsoletus ensemble. Culicoides imicola Kieffer was only found in Spain and the southernmost part of France. There was a clear spatial trend in the accumulated annual abundance from southern to northern Europe, with the Obsoletus ensemble steadily increasing from 4000 per year in southern Europe to 500,000 in Scandinavia. The Pulicaris ensemble showed a very different pattern, with an increase in the accumulated annual abundance from 1600 in Spain, peaking at 41,000 in northern Germany and then decreasing again toward northern latitudes. For the two species ensembles and C. imicola, the season began between January and April, with later start dates and increasingly shorter vector seasons at more northerly latitudes.

CONCLUSION

We present the first maps of seasonal Culicoides abundance in large parts of Europe covering a gradient from southern Spain to northern Scandinavia. The identified temporal trends and spatial patterns are useful for planning the allocation of resources for international prevention and surveillance programmes in the European Union.

Blood-feeding, susceptibility to infection with Schmallenberg virus and phylogenetics of Culicoides (Diptera: Ceratopogonidae) from the United Kingdom

BACKGROUND

Culicoides biting midges (Diptera: Ceratopogonidae) are responsible for the biological transmission of internationally important arboviruses of livestock. In 2011, a novel Orthobunyavirus was discovered in northern Europe causing congenital malformations and abortions in ruminants. From field studies, Culicoides were implicated in the transmission of this virus which was subsequently named Schmallenberg virus (SBV), but to date no assessment of susceptibility to infection of field populations under standardised laboratory conditions has been carried out. We assessed the influence of membrane type (chick skin, collagen, Parafilm M®) when offered in conjunction with an artificial blood-feeding system (Hemotek, UK) on field-collected Culicoides blood-feeding rates. Susceptibility to infection with SBV following blood-feeding on an SBV-blood suspension provided via either (i) the Hemotek system or via (ii) a saturated cotton wool pledglet was then compared. Schmallenberg virus susceptibility was defined by RT-qPCR of RNA extractions of head homogenates and related to Culicoides species and haplotype identifications based on the DNA barcode region of the mitochondrial cytochrome c oxidase 1 (cox1) gene.

RESULTS

Culicoides blood-feeding rates were low across all membrane types tested (7.5% chick skin, 0.0% for collagen, 4.4% Parafilm M®, with 6029 female Culicoides being offered a blood meal in total). Susceptibility to infection with SBV through membrane blood-feeding (8 of 109 individuals tested) and pledglet blood-feeding (1 of 94 individuals tested) was demonstrated for the Obsoletus complex, with both C. obsoletus (Meigen) and C. scoticus Downes & Kettle susceptible to infection with SBV through oral feeding. Potential evidence of cryptic species within UK populations was found for the Obsoletus complex in phylogenetic analyses of cox1 DNA barcodes of 74 individuals assessed from a single field-site.

CONCLUSIONS

Methods described in this study provide the means to blood-feed Palaearctic Culicoides for vector competence studies and colonisation attempts. Susceptibility to SBV infection was 7.3% for membrane-fed members of the subgenus Avaritia and 1.1% for pledglet-fed. Both C. obsoletus and C. scoticus were confirmed as being susceptible to infection with SBV, with potential evidence of cryptic species within UK Obsoletus complex specimens, however the implications of cryptic diversity in the Obsoletus complex on arbovirus transmission remains unknown.

First molecular identification of the vertebrate hosts of Culicoides imicola in Europe and a review of its blood-feeding patterns worldwide: implications for the transmission of bluetongue disease and African horse sickness

Culicoides (Diptera: Ceratopogonidae) are vectors of pathogens that affect wildlife, livestock and, occasionally, humans. Culicoides imicola (Kieffer, 1913) is considered to be the main vector of the pathogens that cause bluetongue disease (BT) and African horse sickness (AHS) in southern Europe. The study of blood-feeding patterns in Culicoides is an essential step towards understanding the epidemiology of these pathogens. Molecular tools that increase the accuracy and sensitivity of traditional methods have been developed to identify the hosts of potential insect vectors. However, to the present group's knowledge, molecular studies that identify the hosts of C. imicola in Europe are lacking. The present study genetically characterizes the barcoding region of C. imicola trapped on farms in southern Spain and identifies its vertebrate hosts in the area. The report also reviews available information on the blood-feeding patterns of C. imicola worldwide. Culicoides imicola from Spain feed on blood of six mammals that include species known to be hosts of the BT and AHS viruses. This study provides evidence of the importance of livestock as sources of bloodmeals for C. imicola and the relevance of this species in the transmission of BT and AHS viruses in Europe.

Bluetongue virus infection in naïve cattle: Identification of circulating serotypes and associated Culicoides biting midge species in Trinidad

To better understand risks associated with trading cattle, it is important to know which serotypes of Bluetongue virus (BTV) are circulating within the exporting and importing country. Hence, this study was conducted to identify the circulating serotypes of BTV in Trinidad. Blood samples were collected monthly from sixty BTV- naïve imported cattle over a six month period after their arrival in the country. Virological (PCR and virus isolation) and serological (ELISA) analyses were carried out on the samples and CDC light traps were placed near the cattle enclosure to trap and identify the species of Culicoides biting midges that were present. All of the cattle seroconverted for BTV antibodies within three months of their arrival in the country and real-time reverse transcription PCR (rRT-PCR) detected BTV-RNA in the samples throughout the remainder of the study. The patterns of infection observed in the cattle indicated serial infections with multiple serotypes. A combination of BTV serotype-specific rRT-PCR on the original blood samples and virus isolation followed by serotype-specific rRT-PCR on selected samples, confirmed the presence of BTV serotypes 1, 2, 3, 5, 12 and 17. This is the first report of BTV-2 and BTV-5 in Trinidad. Light-suction traps placed in close proximity to the cattle predominantly trapped Culicoides insignis Lutz 1913 species (96%), with a further six Culicoides species making up the remaining 4% of trapped samples. The circulation of multiple BTV serotypes in Trinidad underlines the need for regular surveillance, which will contribute to the development of risk assessments for trade in livestock.

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.