Differentiation of <I>Culicoides obsoletus</I> and <I>Culicoides scoticus</I> (Diptera: Ceratopogonidae) Based on Mitochondrial Cytochrome Oxidase Subunit I

Abstract

Culicoides obsoletus (Meigen) and Culicoides scoticus Downes & Kettle (Diptera: Ceratopogonidae) are sibling species of the Obsoletus group. This group comprises species of biting midges that are suspect vectors of bluetongue virus (family Reoviridae, genus Orbivirus, BTV) and African horse sickness virus (family Reoviridae, genus Orbivirus, AHSV). BTV and AHSV have been isolated several times from females of this group, although it has not been possible to determine the particular species harboring the virus, because of the inability to clearly identify the females of each species based on morphology. Both sexes of C. obsoletus and C. scoticus midges from Catalonia and the Balearics (Spain) were sequenced for the mitochondrial gene cytochrome oxidase subunit I (COI), and these sequences were analyzed to determine intra- and interspecific genetic variability. Species-specific primers for C. obsoletus and C. scoticus were designed and a polymerase chain reaction (PCR)-based diagnostic assay based on the COI gene and using a hemi-nested PCR technique was developed for reliably distinguishing the females of both species. The species-specific PCR diagnostic was compared with morphological discrimination of C. obsoletus and C. scoticus females. The morphologic characters were not fully reliable.

Phenotypic differentiation and phylogenetic signal of wing shape in western European biting midges, Culicoides spp., of the subgenus Avaritia

“…As species of the Obsoletus group cannot be differentiated solely by wing pigmentation, males were identified to species level by examination of genitalias (Kremer, 1965), whereas females were identified by species-specific PCR assays (Pagès & Sarto i Monteys, 2005;Nolan et al, 2007). Specimens from C. newsteadi N2, previously employed in Pagès et al (2009) and Muñoz-Muñoz et al (2011), were assigned to a specific category by means of species-specific PCR assays (Pagès et al, 2009).…”

“…Species-specific PCR assays targeting the mitochondrial COI gene were performed (Pagès & Sarto i Monteys, 2005;Nolan et al, 2007). Sequencing and phylogenetic analyses were based on a fragment of the mtDNA COI gene.…”

“…As correct identification of disease vectors is essential in transmission risk assessment, recent efforts have centred upon developing molecular and morphological tools that allow a reliable discrimination between similar species of the Obsoletus group (Cêtre-Sossah et al, 2004;Pagès & Sarto i Monteys, 2005;Mathieu et al, 2007;Nolan et al, 2007;Augot et al, 2010;Nielsen & Kristensen, 2011). In spite of the advantages of employing morphometrics in cryptic species identification and the widespread use of this methodological approach in other biological disciplines, few studies have attempted to discriminate between similar species of Culicoides using multivariate analysis of continuous traits (exceptions are Pagès et al, 2009;Augot et al, 2010).…”

Efficacy of Oxyfly™ on Culicoides species—the vectors of Bluetongue virus—and other insects

“…This enduring effect of the insecticide is apparently due to the microencapsulation of the product (Oxyfly™). Since in Southern Europe the same species of the genus Culicoides may occur, a long-lasting indoor spray would help against the transmission of arriving Bluetongue viruses either from North or South (Pages and Monteys (2005).…”

Bluetongue in Europe: vectors, epidemiology and climate change

“…However, the females of the four species that make up the C. obsoletus group (C. chiopterus, C. dewulfi, C. obsoletus s.l. and C. scoticus) cannot be consistently differentiated from one another on the basis of morphology (Pagès and Sarto I Monteys 2005), making estimation of the competence of the individual species difficult. The recent development of molecular techniques to differentiate the C. obsoletus group species (Mathieu et al 2007;Nolan et al 2007) promises to enable the measurement of BTV competence at the species level.…”