The European vectors of Bluetongue virus: are there species complexes, single species or races in Culicoides obsoletus and C. pulicaris detectable by sequencing ITS-1, ITS-2 and 18S-rDNA?

Abstract

When studying the vectorship of Culicoides species during the outbreak of Bluetongue disease (BTD) in Central Europe, the question arose whether the most common species and additionally proven vectors of BTV (C. obsoletus and C. pulicaris) are definitive species or do they belong to so-called complexes, since the determination based on morphological criteria is not very significant and knowledge on the life cycles is poor or even absent. Therefore, the present molecular biological study on their ITS-1, ITS-2 and 18SrDNA characteristics was initiated to investigate specimens, which had been determined by their wing morphology during an entomological monitoring in the years 2007 and 2008 at 91 farms in Germany (Mehlhorn et al. 2009). This study revealed novel types respectively different forms, which appeared very similar to Culicoides obsoletus, but showed slightly varying wing patterns. The molecular biological data were compared to those in data banks and combined to provisional dendrograms. The ITS-1 and ITS-2 analysis showed that the specimens determined in the monitoring as C. obsoletus inclusive those with different wing pattern correlate significantly with the data of C. obsoletus in the data banks and surrounded the data bank specifications of C. montanus and C. scoticus so closely that the latter might be only hardly separate species. A similar interpretation can also be drawn when looking at the 18S rDNA dendrogram. Thus, C. scoticus and C. montanus might be races of C. obsoletus rather than separate species. With respect to the ITS-1 and ITS-2 characteristics of C. pulicaris females, which morphologically and by size can be significantly differentiated from C. obsoletus, it was seen that this species is significantly situated on another rame of the dendrograms and in very close relationship to C. punctatus and C. lupicaris, so that the latter might also be only races of C. pulicaris. One of the two other most common species found in Northrhine-Westfalia-C. festivipennis-belongs to the rame of the dendrogram, where C. pulicaris is situated close to C. circumscriptus, while the other common species (C. nubeculosus) has its place close to C. puncticollis and C. variipennis on the rame, where C. obsoletus is found. Thus, this paper again clearly points out that the question "what is a definite species" is far from being solved, if the life cycle is not defined and morphology misleading. However, it also became clear that C. obsoletus and C. pulicaris are Europe-wide occurring species and that several other clearly described separate species are probably only races.

Suggesting synonymies? Comments on Kiehl et al. (2009) “The European vectors of Bluetongue virus: are there species complexes, single species or races in Culicoides obsoletus and C. pulicaris detectable by sequencing ITS-1, ITS-2 and 18S-rDNA?”

“…Kiehl et al (2009) carried out phylogenetic studies using different molecular markers on Palaearctic species and according to base differences concluded that two synonymies are present within the Obsoletus group. The authors stated that C. scoticus Downes and Kettle 1952 and C. montanus Shakirzjanova 1952 are a "race" of C. obsoletus (Meigen 1818) and should not be considered as separate species.…”

The geographical distribution and first molecular analysis of Culicoides Latreille (Diptera: Ceratopogonidae) species in the Southern and Southeastern Turkey during the 2012 outbreak of bovine ephemeral fever

“…For the molecular detection and identification of Culicoides specimens, many PCR-based methods have been developed. The ITS-1 gene of Culicoides genome is suggested as a reliable and useful region for diagnosis and genetic investigations of midges (Cetre-Sossah et al 2004;Kiehl et al 2009a;Perrin et al 2006). The ITS-1 gene was also used as a reliable marker in correct molecular identification of Culicoides species in this study.…”

“…Several molecular tools and markers have been developed for identification and phylogenetic analysis describing their genetic relationship. The first internal transcribed spacer (ITS-1) gene of ribosomal DNA (rDNA) is suggested as good phylogenetic molecular marker useful for phylogenetic studies (Cetre-Sossah et al 2004;Kiehl et al 2009a;Perrin et al 2006).…”

Morphological and molecular identification of species of the Obsoletus group (Diptera: Ceratopogonidae) in Scandinavia

“…More recently, Baldet et al (2008) postulated that it is impossible to separate the females of C. obsoletus and C. scoticus by morphological characters, and in some reports, the four species or at least the females of C. obsoletus and C. scoticus are described or grouped as one entity (Mehlhorn et al 2008;Meiswinkel et al 2007) and suggested to be races rather than species (Kiehl et al 2009). Morphological and molecular characters together support the existence of C. obsoletus and C. scoticus as two taxa (Garros et al 2010), as previously confirmed with a phylogenetic tree-based study (Nolan et al 2007).…”