Changes of the abundance of Culicoides obsoletus s.s. and Culicoides scoticus in Southwest Germany identified by a PCR-based differentiation

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

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

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 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.

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.

Mayfly and fish species identification and sex determination in bleak (Alburnus alburnus) by MALDI-TOF mass spectrometry

Besides food quality control of fish or cephalopods, the novel mass spectrometry (MS) approaches could be effective and beneficial methods for the investigation of biodiversity in ecological research. Our aims were to verify the applicability of MALDI-TOF MS in the rapid identification of closely related species, and to further develop it for sex determination in phenotypically similar fish focusing on the low mass range. For MALDI-TOF MS spectra analysis, ClinProTools software was applied, but our observed classification was also confirmed by Self Organizing Map. For verifying the wide applicability of the method, brains from invertebrate and vertebrate species were used in order to detect the species related markers from two mayflies and eight fish as well as sex-related markers within bleak. Seven Ephemera larvae and sixty-one fish species related markers were observed and nineteen sex-related markers were identified in bleak. Similar patterns were observed between the individuals within one species. In contrast, there were markedly diverse patterns between the different species and sexes visualized by SOMs. Two different Ephemera species and male or female fish were identified with 100% accuracy. The various fish species were classified into 8 species with a high level of accuracy (96.2%). Based on MS data, dendrogram was generated from different fish species by using ClinProTools software. This MS-based dendrogram shows relatively high correspondence with the phylogenetic relationships of both the studied species and orders. In summary, MALDI-TOF MS provides a cheap, reliable, sensitive and fast identification tool for researchers in the case of closely related species using mass spectra acquired in a low mass range to define specific molecular profiles. Moreover, we presented evidence for the first time for determination of sex within one fish species by using this method. We conclude that it is a powerful tool that can revolutionize ecological and environmental research.

Bluetongue: control, surveillance and safe movement of animals

The performance of different bluetongue control measures related to both vaccination and protection from bluetongue virus (BTV) vectors was assessed. By means of a mathematical model, it was concluded that when vaccination is applied on 95% of animals even for 3 years, bluetongue cannot be eradicated and is able to re‐emerge. Only after 5 years of vaccination, the infection may be close to the eradication levels. In the absence of vaccination, the disease can persist for several years, reaching an endemic condition with low level of prevalence of infection. Among the mechanisms for bluetongue persistence, the persistence in the wildlife, the transplacental transmission in the host, the duration of viraemia and the possible vertical transmission in vectors were assessed. The criteria of the current surveillance scheme in place in the EU for demonstration of the virus absence need revision, because it was highlighted that under the current surveillance policy bluetongue circulation might occur undetected. For the safe movement of animals, newborn ruminants from vaccinated mothers with neutralising antibodies can be considered protected against infection, although a protective titre threshold cannot be identified. The presence of colostral antibodies interferes with the vaccine immunisation in the newborn for more than 3 months after birth, whereas the minimum time after vaccination of animal to be considered immune can be up to 48 days. The knowledge about vectors ecology, mechanisms of over‐wintering and criteria for the seasonally vector‐free period was updated. Some Culicoides species are active throughout the year and an absolute vector‐free period may not exist at least in some areas in Europe. To date, there is no evidence that the use of insecticides and repellents reduce the transmission of BTV in the field, although this may reduce host/vector contact. By only using pour‐on insecticides, protection of animals is lower than the one provided by vector‐proof establishments.

This publication is linked to the following EFSA Supporting Publications article: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2017.EN-1182/full, http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2017.EN-1171/full

Emergence of Culicoides obsoletus group species from farm-associated habitats in Germany

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) may transmit several arboviruses to ruminant livestock. The species of the Obsoletus group are considered to be among the most important vectors of bluetongue virus (BTV) in northern Europe. As agricultural environments offer suitable habitats for the development of their immature stages, the emergence of adult Culicoides from potential breeding sites was investigated at 20 cattle farms throughout Germany in 2012 and 2013. In analyses of species-specific habitat preferences and relationships between Culicoides abundance in breeding substrates and their physicochemical characteristics, dungheaps emerged as the most important substrate for the development of Culicoides obsoletus sensu stricto (s.s.) (Meigen), whereas Culicoides chiopterus (Meigen) and Culicoides dewulfi Goetghebuer were generally restricted to cowpats. A decreasing pH value was associated with a higher abundance or a higher probability of observing these three species. Furthermore, the abundance of C. obsoletus s.s. was positively related to increasing moisture. Dungheaps were very productive breeding sites for this species and are therefore suggested as a target for potential control measures.

Comparison of matrix-assisted laser desorption ionization-time of flight mass spectrometry and molecular biology techniques for identification of Culicoides (Diptera: ceratopogonidae) biting midges in senegal

Biting midges of the genus Culicoides are implicated as vectors for a wide variety of pathogens. The morphological identification of these arthropods may be difficult because of a lack of detailed investigation of taxonomy for this species in Africa. However, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) profiling is efficient for arthropod identification at the species level. This study established a spectrum database of Culicoides spp. from Senegal using MALDI-TOF. Identification of Culicoides insects to the species level before mass spectrometry was performed on the basis of morphological characters. MALDI-TOF MS reference spectra were determined for 437 field-caught Culicoides of 10 species. The protein profiles of all tested Culicoides revealed several peaks with mass ranges of 2 to 20 kDa. In a validation study, 72 Culicoides specimens in the target species were correctly identified at the species level with a similarity of 95 to 99.9%. Four Culicoides protein profiles were misidentified. Nevertheless, six SuperSpectra (C. imicola, C. enderleini, C. oxystoma, C. kingi, C. magnus, and C. fulvithorax) were created. Abdomens of midges were used to amplify and sequence a portion of the mitochondrial cytochrome oxidase I gene (COI). The results obtained using the MALDI-TOF MS method were consistent with the morphological identification and similar to the genetic identification. Protein profiling using MALDI-TOF is an efficient approach for the identification of Culicoides spp., and it is economically advantageous for approaches that require detailed and quantitative information of vector species that are collected in field. The database of African Culicoides MS spectra created is the first database in Africa. The COI sequences of five Culicoides species that were previously noncharacterized using molecular methods were deposited in GenBank.

Community analysis of biting midges (Culicoides Latr.) on livestock farms in Denmark

This study presents descriptive statistics and community analysis of adult biting midges trapped at 16 livestock farms by means of light traps on Zealand and Lolland-Falster, Denmark. A total of 9,047 male and female Culicoides divided into 24 species, were caught. Biotic and abiotic factors ranging from presence of different host species (cattle or sheep/goats), presence of small woody areas or wetlands in the surrounding landscape, and agricultural practice (organic or conventional) were included in the community analysis. Only differences in the Culicoides communities between conventional and organic practices were tested significantly different. Total numbers of Culicoides individuals were higher on the organic farms than on the conventional farms. The larger loads of biting midges on the organic farms may be due to free-ranging animals that attracted the midges on pastures and carried them to the stable environment (the cattle of the conventional farms were held inside the stables). Presence of deciduous trees within 500 m of the farms resulted in higher numbers of Culicoides obsoletus s.s., while presence of wetlands increased the numbers of Culicoides punctatus and Culicoides pulicaris. Furthermore, Culicoides riethi and Culicoides puncticollis (subgenus Monoculicoides) were recorded in high numbers on individual farms. C. puncticollis was found for the first time in Denmark and so far only recorded from Zealand.

Species determination of Culicoides biting midges via peptide profiling using matrix-assisted laser desorption ionization mass spectrometry

Background

Culicoides biting midges are vectors of bluetongue and Schmallenberg viruses that inflict large-scale disease epidemics in ruminant livestock in Europe. Methods based on morphological characteristics and sequencing of genetic markers are most commonly employed to differentiate Culicoides to species level. Proteomic methods, however, are also increasingly being used as an alternative method of identification. These techniques have the potential to be rapid and may also offer advantages over DNA-based techniques. The aim of this proof-of-principle study was to develop a simple MALDI-MS based method to differentiate Culicoides from different species by peptide patterns with the additional option of identifying discriminating peptides.

Methods

Proteins extracted from 7 Culicoides species were digested and resulting peptides purified. Peptide mass fingerprint (PMF) spectra were recorded using matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) and peak patterns analysed in R using the MALDIquant R package. Additionally, offline liquid chromatography (LC) MALDI-TOF tandem mass spectrometry (MS/MS) was applied to determine the identity of peptide peaks in one exemplary MALDI spectrum obtained using an unfractionated extract.

Results

We showed that the majority of Culicoides species yielded reproducible mass spectra with peak patterns that were suitable for classification. The dendrogram obtained by MS showed tentative similarities to a dendrogram generated from cytochrome oxidase I (COX1) sequences. Using offline LC-MALDI-TOF-MS/MS we determined the identity of 28 peptide peaks observed in one MALDI spectrum in a mass range from 1.1 to 3.1 kDa. All identified peptides were identical to other dipteran species and derived from one of five highly abundant proteins due to an absence of available Culicoides data.

Conclusion

Shotgun mass mapping by MALDI-TOF-MS has been shown to be compatible with morphological and genetic identification of specimens. Furthermore, the method performs at least as well as an alternative approach based on MS spectra of intact proteins, thus establishing the procedure as a method in its own right, with the additional option of concurrently using the same samples in other MS-based applications for protein identifications. The future availability of genomic information for different Culicoides species may enable a more stringent peptide detection based on Culicoides-specific sequence information.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-3305-7-392) contains supplementary material, which is available to authorized users.

The Mondrian matrix: Culicoides biting midge abundance and seasonal incidence during the 2006-2008 epidemic of bluetongue in the Netherlands

During the northern Europe epidemic of bluetongue (BT), Onderstepoort-type blacklight traps were used to capture Culicoides Latreille (Diptera: Ceratopogonidae) biting midges weekly between November 2006 and December 2008 on 21 livestock farms in the Netherlands. Proven and potential vectors for the bluetongue virus (BTV) comprised almost 80% of the midges collected: the Obsoletus complex, constituting C. obsoletus (Meigen) and C. scoticus Downes & Kettle (44.2%), C. dewulfi Goetghebuer (16.4%), C. chiopterus (Meigen) (16.3%) and C. pulicaris (Linnaeus) (0.1%). Half of the 24 commonest species of Culicoides captured completed only one (univoltine) or two (bivoltine) generations annually, whereas multivoltine species (including all BTV vectors) cycled through five to six generations (exceeding the one to four generations calculated in earlier decades). Whether this increment signals a change in the phenology of northern Europe Culicoides or simply is an adaptive response that manifests during warmer episodes, thus heightening periodically the incursive potential of midge-borne arboviruses, remains to be clarified. Culicoides duddingstoni Kettle & Lawson, C. grisescens Edwards, C. maritimus Kieffer, C. pallidicornis Kieffer and C. riethi Kieffer are new records for the biting midge fauna of the Netherlands. It is suggested that C. punctatus (Meigen) be added to the European list of vector Culicoides.

Monitoring bluetongue virus vectors in Andalusia (SW Europe): Culicoides species composition and factors affecting capture rates of the biting midge Culicoides imicola

In this work, we summarize the results of captures of Culicoides species in Andalusia (S Spain) during 2007-2008. Four out of the 15 midge species-Culicoides imicola, Culicoides obsoletus complex, Culicoides pulicaris complex, and Culicoides nubeculosus-accounted for 80.7 % of captures (n = 68,190). Captures were seasonal and mostly occurred in May-November. The overall number of Culicoides specimens captured and the mean number of caught per trap were higher in 2007. We used an information-theoretic approach to analyze whether environmental factors (e.g., weather, altitude above the sea level, distance of the trap from the ground, distance to animals, and land use) affected C. imicola capture probability and success. Mean temperature and rainfall (both integrated into the Gaussen index), distance of traps to host animals, and trap height above the ground were the main factors explaining variance in capture rates in the Bluetongue Entomologic Surveillance Andalusian Program (BESAP). However, all of these patterns strongly varied among traps. As previously remarked by other authors, standardized capture methods and protocols for trap use are needed to ensure that results obtained in different geographical areas and/or periods are comparable.

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

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

Evaluation of matrix-assisted laser desorption/ionization time of flight mass spectrometry for characterization of Culicoides nubeculosus biting midges

Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) has shown promise in species identification of insect species. We evaluated its potential to consistently characterize laboratory-reared biting midges of the species Culicoides nubeculosus (Meigen) (Diptera: Ceratopogonidae). Twenty-one reproducible potential biomarker masses for C. nubeculosus were identified under different experimental treatments. These treatments included the homogenization of insects in either water or known concentrations of formic acid. The biomarker masses were present independent of age, gender and different periods of storage of individuals in 70% ethanol (a standard preservation method). It was found that the presence of blood in females reduced the intensity of the MALDI-TOF pattern, necessitating the removal of the abdomen before analysis. The protein profiles of a related non-biting midge, Forcipomyia sp. (Diptera: Ceratopogonidae), and of Aedes japonicus japonicus (Theobald) (Diptera: Culicidae) mosquitoes were also examined and were distinctly different. These findings provide preliminary data to optimize future studies in differentiation of species within the Culicoides genus using MALDI-TOF MS which is a rapid, simple, reliable and cost-effective technique.

Genetic structure and population dynamics of the biting midges Culicoides obsoletus and Culicoides scoticus: implications for the transmission and maintenance of bluetongue

Culicoides species belonging to the Obsoletus complex (Diptera: Ceratopogonidae) have been indicated as primary bluetongue (BT) vectors in many European countries and their possible involvement in the maintenance and overwintering of BT viruses has been suggested, even in regions where Culicoides imicola Keiffer is the main vector. The Obsoletus complex includes two predominant taxa, Culicoides obsoletus (Meigen) and Culicoides scoticus Downes & Kettle. However, the role played by each species in the epidemiology of BT is still unknown. Taxonomic identification is mainly based on the morphology of male genitalia and the lack of other reliable diagnostic features makes the screening of trap-collected vector populations, mainly females, particularly difficult. Although molecular markers have facilitated species identification, little information is yet available on the biology, abundance and population dynamics of the two taxa. The aim of this work was to investigate the genetic profile and temporal distribution of C. obsoletus and C. scoticus by using isozyme electrophoresis applied to adult midges, collected weekly at two selected farms in southern Sardinia. A total of nine enzyme loci were analysed and five of them provided diagnostic allozyme markers (Hk, Mdh, Pgi, Idh-1 and Idh-2). Nei's genetic distance between the two taxa was in the range of other well-separated taxa (D = 1.792), supporting their status as true species. Culicoides scoticus represented almost 61% of the 562 specimens analysed; its genetic structure was characterized by a very low level of intra-population variation (mean heterozygosity H(e) = 0.019) and higher genetic divergence between populations (F(ST) = 0.0016) than in C. obsoletus. The latter species had significantly more heterozygotes (H(e) = 0.123), a higher percentage of polymorphic loci, and no inter-population differentiation (F(ST) ≅ 0). We suggest that different biological and ecological constraints, such as breeding habitat requirements, may contribute to shaping the genetic profiles of C. scoticus and C. obsoletus. However, enough gene flow was maintained between populations of each species as no spatial and temporal structuring was sustained by Fisher's exact probability test (P > 0.5). The seasonal distributions of C. scoticus and C. obsoletus only partially overlapped: both species were mainly found early in the year, when the main vector, C. imicola, was present in low numbers, and peaked in abundance in April and May. Culicoides scoticus was predominant until May, decreased rapidly in the following months and increased again in winter, whereas C. obsoletus decreased more slowly and was still present in early summer. Consequently, C. scoticus may be a good candidate for playing a role in the transmission and maintenance of BT virus in Sardinia, as well as in other Mediterranean countries, during the months of late winter and early spring when the seroconversion of sentinel animals is still occurring in the absence of the main vector.

Contribution to the knowledge of Culicoides (Diptera: Ceratopogonidae) host preferences in France

Knowledge on host-feeding pattern of blood-sucking insects helps to understand the epidemiology of a vector-born disease. We determined blood meal origin from blood-fed Culicoides thanks to molecular techniques. A set of primers was used to selectively amplify segment of vertebrates' prepronociceptin gene from abdomen of engorged Culicoides (Diptera: Ceratopogonidae). Vertebrate DNA was successfully amplified in 91% of blood-fed Culicoides assayed. Direct sequencing and comparison of resultant sequences with sequences in GenBank, using BLAST, lead to the specific identification of the host in 100% of the cases. A total of 157 blood-fed females belonging to 13 different Culicoides' species were captured thanks to light traps in different areas of France between 2008 and 2009. Blood meal origin was determined for 143 blood-fed midges: 59 Culicoides obsoletus, 18 Culicoides dewulfi, 16 Culicoides scoticus, 11 Culicoides chiopterus, 10 Culicoides lupicaris, 1 Culicoides pulicaris, 8 Culicoides punctatus, 10 Culicoides pallidicornis, 3 Culicoides achrayi, 2 Culicoides furcillatus, 3 Culicoides brunnicans, 1 Culicoides picturatus and 1 Culicoides poperinghensis. The predominant species in our study belong to the C. obsoletus complex; they are considered as putative vectors of Bluetongue virus in the north of Europe. C. chiopterus sampled fed only on cattle, while blood meal origin of C. dewulfi, C. obsoletus and C. scoticus was diversified. In our sampling, we found that midges were fed mainly on cattle (54%), rabbits (20%), horses (17%), sheep (4%), pigs or wild boars (4%) and human (1%). Cattle DNA was found in at least 11 different species of Culicoides assayed.

Discrimination of Culicoides obsoletus and Culicoides scoticus, potential bluetongue vectors, by morphometrical and mitochondrial cytochrome oxidase subunit I analysis

Biting midges of the Culicoides obsoletus Meigen species complex (Diptera: Ceratopogonidae) are increasingly suspected as vectors of the recent emergence of bluetongue virus in Europe. Within this complex, identification of the C. obsoletus and Culicoides scoticus females is considered as difficult or sometimes not possible while the identification of males is easy, based on genitalia observation. Nolan et al. (2007) concluded that the distinction of C. obsoletus and C. scoticus females is not possible according to morphology but require molecular analyses. In 2010, the identification of biting midges is done under a stereomicroscope without specific identification within the C. obsoletus species complex. However, such a specific identification distinguishing C. obsoletus s. str. and C. scoticus s. str. is crucial to identify the European competent vectors of the virus, their relative abundances and then accurately assess the risk. We performed morphometric analyses of head, genitalia and thorax of females combined with sequencing of the cytochrome oxidase I barcode fragment of mitochondrial DNA on 88 specimens in order to have a molecular identification of our sampled species. As we knew the actual species of individuals thanks to molecular results, we explored the discriminant power of 15 morphometric variables to distinguish the females according to their species. Multivariate analyses were performed on the morphometric measurements to identify and validate a combination of variables leading to an accurate species identification. It appears that females of C. obsoletus and C. scoticus can be accurately distinguished based on only four variables: width between chitinous plates, length and width of spermathecae1 and length of spermatheca2. This approach should improve the accuracy of morphologically-based species identification.

Bluetongue disease in Germany (2007-2008): monitoring of entomological aspects

In the summer of 2006, a bluetongue epidemic started in the border area of Belgium, The Netherlands, and Germany, spread within 2 years over large areas of Western and Central Europe, and caused substantial losses in farm ruminants. Especially sheep and cattle were severely affected, leading to a case-fatality ratio of nearly 40% in sheep (Conraths et al., Emerg Inf Dis 15(3):433-435, 2009). The German federal ministry of food, agriculture, and consumer protection (BMELV) established a countrywide monitoring on the occurrence of the vectors of this virus, i.e., midges (family Ceratopogonidae) of the genus Culicoides. The monitoring was done on 91 sites, most of which were localized in the 150-km restriction zone that existed in December 2006. A grid consisting of 45 x 45 km(2) cells was formed that covered the monitoring area. As a rule, one trap was placed into each grid cell. The monitoring program started at the end of March 2007 and lasted until May 2008. It included the catching of midges by ultraviolet light traps-done each month from days 1 until 8, the selection of midges of the Culicoides obsoletus, Culicoides pulicaris group, and other Culicoides spp., the testing of midges for bluetongue virus (BTV) by polymerase chain reaction (PCR), and the daily registration of weather data at each trap site for the whole monitoring period. The following main results were obtained: (1) Members of the C. obsoletus group were most commonly found in the traps, reaching often 3/4 of the catches. The African and South European vector of BTV-the species Culicoides imicola-was never found. (2) Members of the C. obsoletus group were most frequently found infected with BTV besides a few cases in the C. pulicaris group and other species. (3) Members of the C. obsoletus group were also found in winter. Their numbers were reduced, however, and they were caught mostly close to stables. Therefore, a true midge-free period does not exist during the year in Germany. (4) The amounts of midges caught daily depended on the weather conditions. If it was cold and/or windy, the traps contained only a few specimens. Since the months from January to May 2008 were considerably colder (at all farms) than their correspondents in 2007, the growing of the population of midges started 2-3 months later in 2008 than in 2007. (5) The highest populations of midges occurred in both years (2007 and 2008) during the months September and October. This corresponded significantly to the finding of highest numbers of infected midges and to the number of diseased cattle and sheep during these 2 months. (6) It is noteworthy that in general, the first virus-positive midges of the species C. obsoletus were found about 1 1/2 months later than the first clinical cases had occurred or later than the first PCR-proven virus-positive sentinel animals had been documented. In 2007, the first BTV-positive cattle were detected in May in North Rhine-Westphalia, while the first positive Culicoides specimens were only found in August on the same farm. Evaluating these main results of the entomological monitoring and the fact that many wild ruminants have also been infected with BTV, it becomes evident that bluetongue disease has become endemic in Central Europe, and that only constant effort including vaccination and perhaps also insecticidal protection of cattle and sheep will keep the economical losses at a reasonable level. The following papers (1-10) in this journal will contribute more details obtained from this worldwide unique entomological monitoring: Bartsch et al. 2009; Bauer et al. 2009; Stephan et al. 2009; Clausen et al. 2009; Hörbrand and Geier 2009; Kiehl et al. 2009; Mehlhorn et al. 2009; Kiel et al. 2009; Vorsprach et al. 2009; Balczun et al. 2009.