Genetic analyses of Culicoides peregrinus (Diptera: Ceratopogonidae) reveal population differentiation in southern India a hotspot of bluetongue disease outbreaks and lack of gene flow across its range

Among India's 7 potential vectors of bluetongue virus (BTV), Culicoides peregrinus has assumed importance due to the recent isolation of BTV-23, with several severe bluetongue disease (BTD) outbreaks in Southern India and high abundance throughout India. These factors warrant the elucidation of its genetic structure across various physiographic regions. Adult Culicoides were captured from 14 collection locations across different physiographic areas of India. The study used 2 genetic markers, ie mitochondrial cytochrome oxidase-1 (COX-1) and nuclear ribosomal protein-S2B intron region (EPIC). COX-1 sequences of C. peregrinus from the other areas of its distribution were also considered. A high intraspecific genetic distance, ie 2.46% (within India) and 3.5% (across its distribution range) indicates the possibility of cryptic species. This vector has a relatively uniform genetic structure with a slight difference in the southern Indian population. However, the populations from different countries are genetically distinct and exhibit high genetic distances among themselves. There is evidence of demographic expansion with India as the probable ancestral region with 3 distinct lineages: India-Bangladesh, Thailand-China-Malaysia, and Australia. STRUCTURE analysis using EPIC marker (ribosomal protein-S2B intron region) depicted the distribution of 2 alleles in India but no population substructure. Pairwise FST indicated the south Indian population to have low but significant genetic differentiation with other Indian populations. More fine scale studies to ascertain the genetic differentiation of the Indian population along with direct experimental validation of vector competence is imperative to confirm C. peregrinus as the causative vector of BTD outbreaks.