PCR identification of culicoid biting midges (Diptera, Ceratopogonidae) of the Obsoletus complex including putative vectors of bluetongue and Schmallenberg viruses

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%).

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.

Species Identity, Life History, and Geographic Distance Influence Gut Bacterial Communities in Lab-Reared and European Field-Collected Culicoides Biting midges

Bacteria are part of the insect gut system and influence many physiological traits of their host. Gut bacteria may even reduce or block the transmission of arboviruses in several species of arthropod vectors. Culicoides biting midges are important arboviral vectors of several livestock and wildlife diseases, yet limited information is available on their gut bacterial communities. Addressing this gap will help inform how these communities can be manipulated and ultimately used as novel tools to control pathogens. To assess how bacterial communities change during the life stages of lab-reared C. nubeculosus and C. sonorensis, endosymbiotic bacteria were identified using Illumina sequencing of 16S rRNA and taxonomically characterised. Analyses were conducted to determine how gut bacterial communities in adults are influenced by species identity and geographic distance among biting midge populations. Communities of the two lab-reared Culicoides species significantly changed after pupation and with maturation into 6-day-old adults. Pseudomonas, Burkholderiaceae and Leucobacter bacteria were part of a core community that was trans-stadially transmitted and found throughout their life cycle. Among field-collected biting midges, the bacterial communities were unique for almost each species. Cardinium, Rickettsia and Wolbachia were some of the most abundant bacteria in midges collected from wetlands. Only Pseudomonas was present in high relative abundance in all field-collected species. In this study, species identity, as well as geographic distance, influenced the gut bacterial communities and may partly explain known inter- and intra-species variability in vector competence. Additionally, stably associated bacterial species could be candidates for paratransgenic strategies to control vector-borne pathogens.

The invasive Korean bush mosquito Aedes koreicus (Diptera: Culicidae) in Germany as of 2020

Background

The Korean bush mosquito Aedes koreicus was recently reported to have established a population in western Germany (Wiesbaden) in 2016. The species is difficult to distinguish morphologically from its close relative, the invasive Japanese bush mosquito Ae. japonicus, which is already widely distributed in many parts of Germany, including the area colonised by Ae. koreicus. Genetic confirmation of morphologically identified “Ae. japonicus” collection material, however, had only been done exceptionally before the German Ae. koreicus population became known.

Methods

Dried archived “Ae. japonicus” specimens both from the municipality of Wiesbaden and from deliberately and randomly selected distribution sites all over Germany were re-examined morphologically and genetically for admixture by Ae. koreicus. Moreover, cemeteries in the greater Wiesbaden area were sampled in 2019 and 2020 to check for Ae. koreicus spread. Korean and Japanese bush mosquitoes submitted to the German citizen science mosquito monitoring scheme “Mueckenatlas” in 2019 and 2020 were also subjected to particularly thorough species identification. The ND4 DNA sequences generated in this study in the context of species identification were phylogenetically compared to respective GenBank entries of Ae. koreicus. As a by-product, several genetic markers were evaluated for their suitability to identify Ae. koreicus.

Results

Aedes koreicus specimens could be identified in mosquito collection material and submissions from Wiesbaden from 2015 onwards, suggesting establishment to have happened in the same year as Ae. japonicus establishment. Detections of Ae. koreicus from 2019 and 2020 in Wiesbaden indicate a negligible enlargement of the populated area as described for 2018. Two Ae. koreicus specimens were also submitted from the city of Munich, southern Germany, in 2019 but further specimens could not be identified during immediate local inspections. Comparison of ND4 sequences generated in this and other studies demonstrate a high degree of homology, suggesting that this DNA region is not informative enough for clarification of origins and relationships of Ae. koreicus populations. For genetic identification of Ae. koreicus, PCR primers used for classical CO1 barcoding were found to lead to mismatches and produce no or incorrect amplicons. Alternative CO1 primers or a validated ND4 marker should be used instead.

Conclusions

Aedes koreicus is probably introduced into Germany every now and then but rarely succeeds in becoming established. As with most European populations, the German population is characterised by a limited expansion tendency. Since Ae. koreicus is a potential vector, however, Asian bush mosquitoes found at new places should be examined quite carefully and known distribution areas of Ae. japonicus regularly checked for the presence of Ae. koreicus.

Graphical Abstract

Transcriptome profiling reveals the developmental regulation of NaCl-treated Forcipomyia taiwana eggs

Background

The biting midge, Forcipomyia taiwana, is one of the most annoying blood-sucking pests in Taiwan. Current chemical control methods only target the adult, not the immature stages (egg to pupa), of F. taiwana. Discovering new or alternative tactics to enhance or replace existing methods are urgently needed to improve the effectiveness of F. taiwana control. The egg is the least understood life stage in this pest species but may offer a novel point of control as addition of NaCl to the egg environment inhibits development. Thus, the objective of this study was to use RNA profiling to better understand the developmental differences between wild-type melanized (black) and NaCl-induced un-melanized (pink), infertile F. taiwana eggs.

Results

After de novo assembly with Trinity, 87,415 non-redundant transcripts (Ft-nr) with an N50 of 1099 were obtained. Of these, 26,247 (30%) transcripts were predicted to have long open reading frames (ORFs, defined here as ≥300 nt) and 15,270 (17.5%) transcripts have at least one predicted functional domain. A comparison between two biological replicates each of black and pink egg samples, although limited in sample size, revealed 5898 differentially expressed genes (DEGs; 40.9% of the transcripts with long ORFs) with ≥2-fold difference. Of these, 2030 were annotated to a Gene Ontology biological process and along with gene expression patterns can be separated into 5 clusters. KEGG pathway analysis revealed that 1589 transcripts could be assigned to 18 significantly enriched pathways in 2 main categories (metabolism and environmental information processing). As expected, most (88.32%) of these DEGs were down-regulated in the pink eggs. Surprisingly, the majority of genes associated with the pigmentation GO term were up-regulated in the pink egg samples. However, the two key terminal genes of the melanin synthesis pathway, laccase2 and DCE/yellow, were significantly down-regulated, and further verified by qRT-PCR.

Conclusion

We have assembled and annotated the first egg transcriptome for F. taiwana, a biting midge. Our results suggest that down-regulation of the laccase2 and DCE/yellow genes might be the mechanism responsible for the NaCl-induced inhibition of melanization of F. taiwana eggs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08096-x.

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.

A DNA-based method for distinction of fly artifacts from human bloodstains

Fly artifacts resulting from insect activity could act as confounding factors on a crime scene and interfere with bloodstain pattern analysis interpretation. Several techniques have been proposed to distinguish fly artifacts from human bloodstains based on morphological approach and immunological assay, but a DNA-based method has not been developed so far. Even if in forensic genetic investigations the detection of human DNA is generally the primary goal, fly artifacts can provide useful information on the dynamics of crime events. The present study provides a molecular method to detect fly DNA from artifacts deposited by Calliphora vomitoria after feeding on human blood through the analysis of the mitochondrial cytochrome oxidase gene subunit I (COI). Fly artifacts originated from digestive process and of different morphology spanning from red and brownish/light brown, circular and elliptical stains to artifacts with sperm-like tail or a tear-shaped body were collected. The COI amplification was successfully obtained in 94% of fly artifact samples. The method showed high sensitivity and reproducibility, and no human DNA contamination was observed, offering specificity for use in confirmatory test. This molecular approach permits the distinction of fly artifacts from genuine bloodstains and the identification of fly's species through the COI region sequencing by protocols usually applied in forensic genetic laboratories.

Field studies on breeding sites of Culicoides LATREILLE (Diptera: Ceratopogonidae) in agriculturally used and natural habitats

Culicoides are vectors of pathogens mainly of veterinary importance. To establish targeted vector control measures, it is paramount to comprehend the ecological factors determining their distribution. Therefore, we used emergence traps to sample eight biotopes and assess their potential as breeding sites. Part one of the study investigates agricultural habitats, part two compares four biotopes of a forest-dominated area with less anthropogenic influence, including a physicochemical analysis of soil moisture, pH value and organic content. Thirteen culicoid species were collected, with a strong dominance of the Obsoletus Complex on meadows, and with Culicoides punctatus (Meigen), Culicoides pictipennis (Staeger) and the Obsoletus Complex, to be the most abundant species in the natural habitats. Several co-existing species were found, some of them not having been described before. Our results suggest that ungrazed meadows seem unsuitable as breeding sites. Only the influence of livestock creates adequate conditions for certain midge species. The alder on fen site contained most culicoid species with the highest species diversity. Our study clearly indicates that knowledge of species-specific preferences for environmental habitat conditions (choice of breeding site) in connection to soil conditions is crucial to understand the biology and phenology of midges and their role as vectors of pathogens.

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.

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.

Vector competence of pre-alpine Culicoides (Diptera: Ceratopogonidae) for bluetongue virus serotypes 1, 4 and 8

Background

Bluetongue disease, caused by bluetongue virus serotype 8 (BTV-8), appeared for the first time in the northern part of Europe in 2006, and subsequently rapidly spread causing severe economic losses to the farming industry. The implicated vectors of BTV in Europe are Culicoides species within the subgenus Avaritia (C. chiopterus, C. dewulfi, C. obsoletus and C. scoticus). Epidemiological data from Switzerland have shown that BTV, whose spread was eliminated at an early stage by vaccination campaigns, had not been circulating among livestock at higher altitudes where other species dominate the Culicoides fauna. In this study, we investigated the extent that Culicoides spp. prevailing at higher altitudes (mainly C. grisescens) can act as vectors for BTV.

Methods

Culicoides were collected at farms in the pre-alpine region (two sites at 1550 m above sea level, masl, referred to as pre-alpine I; one site at 2030 masl, pre-alpine II) and, for comparative purposes, from the Swiss Plateau (one site, 650 masl). They were fed on bovine blood/BTV suspensions (BTV-1, 4 or 8) and incubated for eight days under a fluctuating temperature regime (13–25 °C, mean 19 °C), reflecting a mid-summer warm spell in the pre-alpine region. Susceptibility to BTV transmission was assessed from head homogenates by RT-qPCR and virus isolation.

Results

Overall, 9196 female Culicoides were exposed to the three BTV strains through an artificial membrane, with feeding rates of 14–27%. Survival rates of blood-engorged Culicoides females at eight days post-infection depended on both virus serotype and altitude of origin. Virus dissemination (C_q ≤ the cut-off value as determined by serial virus dilutions) was confirmed only for BTV-1 in C. scoticus (dissemination efficiency 22.5%; 9/40) and C. obsoletus (5.6%; 1/18) from the Swiss Plateau area. There was no strong evidence of susceptibility to infection for Culicoides from the pre-alpine area when fed with all BTV strains (BTV-1, 4 and 8).

Conclusions

This study confirms the susceptibility of C. scoticus and C. obsoletus to BTV-1 infection, including under cooler temperatures. Culicoides grisescens, which is highly abundant at higher altitudes, cannot be considered a potential vector under these temperature conditions.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3050-y) contains supplementary material, which is available to authorized users.

Physiological and immunological responses to Culicoides sonorensis blood-feeding: a murine model

Background

Hematophagous Culicoides spp. biting midges are of great agricultural importance as livestock, equine, and wildlife pests and as vectors of the orbiviruses bluetongue, epizootic hemorrhagic disease and African horse sickness. To obtain a blood meal, midges deposit saliva containing allergens, proteases, and anti-hemostatic factors, into the dermis to facilitate feeding. Infected midges deposit virus along with the myriad of salivary proteins during feeding. The extreme efficiency with which midges are able to transmit orbiviruses is not clearly understood, as much is still unknown about the physiological trauma of the bite and immune responses to saliva deposited during feeding. Of particular interest are the first few hours and days after the bite; a critical time period for any midge-transmitted virus to quickly establish a localized infection and disseminate, while avoiding the hosts’ immune responses.

Results

A mouse-midge feeding model using colonized Culicoides sonorensis midges was used to characterize innate mammalian immune responses to blood-feeding. Histological analysis of skin, and cellular and cytokine profiles of draining lymph nodes show Culicoides midge feeding elicited a potent pro-inflammatory Th-mediated cellular response with significant mast cell activation, subcutaneous hematomas, hypodermal edema and dermal capillary vasodilation, and rapid infiltration of leukocytes to the bite sites. Mast cell degranulation, triggered by bite trauma and specifically by midge saliva, was key to physiological and immunological responses and the ability of midges to feed to repletion.

Conclusions

Midge feeding causes physiological and immunological responses that would be highly favorable for rapid infection and systemic dissemination orbiviruses if delivered during blood-feeding. Recruitment of leukocytic cells to bitten skin brings susceptible cell populations in proximity of deposited virus within hours of feeding. Infected cells would drain to lymph nodes, which become hyperplastic in response to saliva, and result in robust viral replication in expanding cell populations and dissemination via the lymph system. Additionally, saliva-induced vasodilation and direct breaches in dermal capillaries by biting mouthparts exposes susceptible vascular endothelial cells, thereby providing immediate sites of virus replication and a dissemination route via the circulatory system. This research provides insights into the efficiency of Culicoides midges as orbivirus vectors.

Activity of Culicoides spp. (Diptera: Ceratopogonidae) inside and outside of livestock stables in late winter and spring

Culicoides Latreille, 1809 midge species are the putative vectors of Bluetongue virus (BTV) and Schmallenberg virus (SBV) in Europe. To gain a better understanding of the epidemiology of the diseases, basic knowledge about the overwintering of the vectors is needed. Therefore, we investigated culicoid activity in relation to air temperature at livestock stables during late winter and spring season. Ceratopogonids were captured weekly indoors and outdoors on three cattle farms, three horse farms and one sheep farm in the federal state of Brandenburg, Germany between January and May, 2015 by BG-Sentinel UV-light suction traps. First seasonal activity was measured inside a sheep barn and cattle stables in mid-March, suggesting the existence of a preceding vector-free period. The first species at all trapping sites were members of the Obsoletus Complex followed by Culicoides punctatus (Meigen), 1804 and Culicoides pulicaris (Linnaeus), 1758 simultaneously. In total, 160 collections were made, including 3465 Culicoides specimens with 2790 (80.6%) of them being members of the Obsoletus Complex. The remaining 675 individuals belonged to six other culicoid species. 59.8% of all Culicoides were collected indoors, and almost five times as many midges were sampled on cattle farms as on horse farms. Cattle farms harboured seven species while only two species were found on the horse and the sheep farms, respectively. Temperatures, husbandry practises and the presence/quality of potential breeding sites might be responsible for the difference in species and numbers of caught specimens between livestock holdings.

Schmallenberg virus infection of ruminants: challenges and opportunities for veterinarians

In 2011, European ruminant flocks were infected by Schmallenberg virus (SBV) leading to transient disease in adult cattle but abortions and congenital deformities in calves, lambs, and goat kids. SBV belonging to the Simbu serogroup (family Bunyaviridae and genus Orthobunyavirus) was first discovered in the same region where bluetongue virus serotype 8 (BTV-8) emerged 5 years before. Both viruses are transmitted by biting midges (Culicoides spp.) and share several similarities. This paper describes the current knowledge of temporal and geographical spread, molecular virology, transmission and susceptible species, clinical signs, diagnosis, prevention and control, impact on ruminant health, and productivity of SBV infection in Europe, and compares SBV infection with BTV-8 infection in ruminants.

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

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

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

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

An unrecognized species of the Culicoides obsoletus complex feeding on livestock in The Netherlands

In studies on Culicoides attacking livestock in the Netherlands, we chanced upon a species of the Obsoletus complex that we do not recognize, but whose dark wing pattern is distinctive. Nine cytochrome c oxidase (CO1) sequences of our so-called 'dark obsoletus' support its status as a separate species, the sequences differing significantly from those representing Culicoides obsoletus (Meigen) (90-91% homology) and Culicoides scoticus Downes & Kettle (87-88% homology). In the last decade, several research groups in Europe have encountered 'mystery species' related to C. obsoletus and in some instances have made their sequences for various genetic loci available in GenBank. These include a CO1 series submitted from Sweden in 2012 (annotated as 'obsoletus 01, 02, or 03 MA-2012') and of which some share a 99% identity with our sequences for 'dark obsoletus'. Without doubt, the series from the Netherlands, along with a portion of the Swedish submissions, together represent a single species ('dark obsoletus'). Whether this species is referable to the Russian Culicoides gornostaevae Mirzaeva recorded recently from Norway, Sweden and Poland, and based solely upon the external morphology of the male, is not clear. The presence in Western Europe of multiple undescribed species related to C. obsoletus means that the taxonomy of this important vector complex is not fully resolved; consequently, we know little about these cryptic species with regard to seasonality, geographic range and host preference. This is undesirable given that Culicoides-borne arboviruses causing disease in livestock are moving more regularly out of the tropics and spreading north into temperate latitudes.

The salivary secretome of the biting midge, Culicoides sonorensis

Culicoides biting midges (Diptera: Ceratopogonidae) are hematophagous insects with over 1400 species distributed throughout the world. Many of these species are of particular agricultural importance as primary vectors of bluetongue and Schmallenberg viruses, yet little is known about Culicoides genomics and proteomics. Detailed studies of members from other blood-feeding Dipteran families, including those of mosquito (Culicidae) and black fly (Simuliidae), have shown that protein components within the insect's saliva facilitate the blood feeding process. To determine the protein components in Culicoides sonorensis midges, secreted saliva was collected for peptide sequencing by tandem mass spectrometry. Forty-five secreted proteins were identified, including members of the D7 odorant binding protein family, Kunitz-like serine protease inhibitors, maltase, trypsin, and six novel proteins unique to C. sonorensis. Identifying the complex myriad of proteins in saliva from blood-feeding Dipteran species is critical for understanding their role in blood feeding, arbovirus transmission, and possibly the resulting disease pathogenesis.

Towards the PCR-based identification of Palaearctic Culicoides biting midges (Diptera: Ceratopogonidae): results from an international ring trial targeting four species of the subgenus Avaritia

Background

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are biological vectors of internationally important arboviruses. To understand the role of Culicoides in the transmission of these viruses, it is essential to correctly identify the species involved. Within the western Palaearctic region, the main suspected vector species, C. obsoletus, C. scoticus, C. dewulfi and C. chiopterus, have similar wing patterns, which makes it difficult to separate and identify them correctly.

Methods

In this study, designed as an inter-laboratory ring trial with twelve partners from Europe and North Africa, we assess four PCR-based assays which are used routinely to differentiate the four species of Culicoides listed above. The assays based on mitochondrial or ribosomal DNA or microarray hybridisation were tested using aliquots of Culicoides DNA (extracted using commercial kits), crude lysates of ground specimens and whole Culicoides (265 individuals), and non-Culicoides Ceratopogonidae (13 individuals) collected from across Europe.

Results

A total of 800 molecular assays were implemented. The in-house assays functioned effectively, although specificity and sensitivity varied according to the molecular marker and DNA extraction method used. The Obsoletus group specificity was overall high (95-99%) while the sensitivity varied greatly (59.6-100%). DNA extraction methods impacted the sensitivity of the assays as well as the type of sample used as template for the DNA extraction.

Conclusions

The results are discussed in terms of current use of species diagnostic assays and the future development of molecular tools for the rapid differentiation of cryptic Culicoides species.

Evaluation of a diagnostic ELISA for insect bite hypersensitivity in horses using recombinant Obsoletus complex allergens

Culicoides spp. of the Obsoletus complex belong to the most important species of midge, involved in causing insect bite hypersensitivity (IBH) in horses in The Netherlands. The aim of the current study was to evaluate seven different Obsoletus complex-derived recombinant allergens (Cul o 1-Cul o 7) and to compare these with Obsoletus complex whole body extract (WBE) in an IgE ELISA, using sera of 194 clinically-confirmed cases of IBH and 175 unaffected horses. The highest test accuracy was obtained with WBE, followed by Cul o 2, 3 and 5. Two ELISAs with a combination of recombinant allergens, Combi-1 (Cul o 3, 5 and 7) and Combi-2 (Cul o 1, 2, 5 and 7) were additionally performed and both resulted in high test accuracies close to that obtained with WBE. Combi-1 resulted in the best sensitivity and specificity, both 89%. Both Combi-1 and Combi-2 performed less well with samples collected in winter, but over 70% of the IBH-affected horses could still be identified. In conclusion, a combination of three Obsoletus complex recombinant allergens (Cul o 3, 5 and 7) could potentially replace Obsoletus complex WBE in an IgE ELISA for diagnosis of IBH in horses.

A new focus of Aedes japonicus japonicus (Theobald, 1901) (Diptera, Culicidae) distribution in Western Germany: rapid spread or a further introduction event?

Background

The Asian bush mosquito, Aedes japonicus japonicus, a potential vector of several viruses, was first detected in Germany in 2008 on the Swiss-German border. In the following years, this invasive species apparently succeeded in establishing populations in southern Germany and in spreading northwards. In 2011, its distribution area already covered large areas of the federal state of Baden-Wurttemberg, and its northernmost German collection point was reported to be close to Stuttgart. Several independent submissions to our laboratories of Ae. j. japonicus specimens in July 2012, originating from the same area in the federal state of North Rhine-Westphalia, western Germany, prompted us to carry out an immediate surveillance in this region in the expectation of finding a further distribution focus of Ae. j. japonicus in Germany.

Methods

After inspecting the places of residence of the collectors of the submitted mosquito specimens, all kinds of water containers in 123 cemeteries in surrounding towns and villages were checked for mosquito developmental stages. These were collected and kept to produce adults for morphological species identification. One specimen per collection site was identified genetically by COI sequence analysis.

Results

Aedes j. japonicus adults and immature stages were found in 36 towns/villages that were checked (29%) over an area of approximately 2,000 km² in southern North Rhine-Westphalia and northern Rhineland Palatinate. The species could not be demonstrated further south when monitoring towards the northernmost previous collection sites in southern Germany. It therefore remains to be elucidated whether the species has entered western Germany from the south, from Belgium in the west where it has been demonstrated to occur locally since 2002, or through a new introduction.

Conclusions

Aedes j. japonicus is obviously much more widely distributed in Germany than previously thought. It appears to be well adapted, to have a strong expansion tendency and to replace indigenous mosquito species. Thus, a further spread is anticipated and elimination seems hardly possible anymore. The vector potency of the species should be reason enough to thoroughly monitor its future development in Germany.

Predicting the spatio-temporal distribution of Culicoides imicola in Sardinia using a discrete-time population model

Background

Culicoides imicola KIEFFER, 1913 (Diptera: Ceratopogonidae) is the principal vector of Bluetongue disease in the Mediterranean basin, Africa and Asia. Previous studies have identified a range of eco-climatic variables associated with the distribution of C. imicola, and these relationships have been used to predict the large-scale distribution of the vector. However, these studies are not temporally-explicit and can not be used to predict the seasonality in C. imicola abundances. Between 2001 and 2006, longitudinal entomological surveillance was carried out throughout Italy, and provided a comprehensive spatio-temporal dataset of C. imicola catches in Onderstepoort-type black-light traps, in particular in Sardinia where the species is considered endemic.

Methods

We built a dynamic model that allows describing the effect of eco-climatic indicators on the monthly abundances of C. imicola in Sardinia. Model precision and accuracy were evaluated according to the influence of process and observation errors.

Results

A first-order autoregressive cofactor, a digital elevation model and MODIS Land Surface Temperature (LST)/or temperatures acquired from weather stations explained ~77% of the variability encountered in the samplings carried out in 9 sites during 6 years. Incorporating Normalized Difference Vegetation Index (NDVI) or rainfall did not increase the model's predictive capacity. On average, dynamics simulations showed good accuracy (predicted vs. observed r corr = 0.9). Although the model did not always reproduce the absolute levels of monthly abundances peaks, it succeeded in reproducing the seasonality in population level and allowed identifying the periods of low abundances and with no apparent activity. On that basis, we mapped C. imicola monthly distribution over the entire Sardinian region.

Conclusions

This study demonstrated prospects for modelling data arising from Culicoides longitudinal entomological surveillance. The framework explicitly incorporates the influence of eco-climatic factors on population growth rates and accounts for observation and process errors. Upon validation, such a model could be used to predict monthly population abundances on the basis of environmental conditions, and hence can potentially reduce the amount of entomological surveillance.

Spatio-temporal occurrence of Culicoides biting midges in the climatic regions of Switzerland, along with large scale species identification by MALDI-TOF mass spectrometry

Background

Culicoides biting midges are incriminated as biological vectors of a number of viruses, e.g. bluetongue virus. In order to define vector-free periods/areas and to assess the vectorial role of the various Culicoides species, a comprehensive knowledge on their spatio-temporal occurrence is required.

Methods

Biting midges were monitored on farm sites with livestock in the defined climatic regions, including high altitudes, of Switzerland by overnight trapping at 12 locations once a week over three years using UV-light traps. Based on morphological features, they were separated into three groups (i.e. Obsoletus, Pulicaris, other Culicoides spp.), and identification to the species level was achieved by protein profiling using MALDI-TOF mass spectrometry.

Results

Around 550,000 biting midges in total were collected, revealing a dominance (82 to 99%) of the Obsoletus group species up to an altitude of 1,200 m and of the Pulicaris group species above 1,500 m (85% at the highest trapping site at 2,130 m). The maximum number of midges collected in a summer night (756 to 19,682) as well as the total number of midges caught over three years (from 6,933 to 149,439) varied highly among the sites, whereas the annual variation in total midge abundance at the locations was statistically insignificant. MALDI-TOF MS of 100 randomly selected individual biting midges per trapping site yielded high quality spectra for 1,187 of the 1,200 (98.9%) specimens of which 1,173 could be assigned to one of the 15 Culicoides species for which biomarker mass sets are available in the reference database.

Conclusions

There are no biting midge-free zones in all of the agriculturally utilized areas (including alpine summer pastures) of Switzerland. Annual variations of midge numbers at the sampled locations were low, indicating that monitoring of midges should preferably be done by investigating a large number of sites for one season instead of few locations for extended periods of time. High throughput species identification of midges by MALDI-TOF MS is feasible, and this technique adds to other recently developed methods for the identification of midges (PCRs in various formats, interactive identification keys), facilitating epidemiological and biological in-depth studies of these important insects.