Chromosome-scale genome of Culicoides brevitarsis provides a resource for comparative and vector biology studies

BACKGROUND: Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are key arbovirus vectors of human and animal health relevance. Understanding the biological and molecular factors influencing arbovirus transmission is essential for informing effective mitigation strategies. Culicoides brevitarsis Kieffer is of particular importance due to its close relationship to cattle, high population abundance in suitable sites, and demonstrated vector capacity for arboviruses. However, limited genomic resources have constrained investigation into its molecular and evolutionary biology, necessitating a chromosome-level genome assembly and comparative genomic analyses. METHODS: A chromosome-level genome assembly of C. brevitarsis was generated using Oxford Nanopore long reads, polished with Illumina short reads, and scaffolded using Hi-C sequencing, followed by genome annotation, comparative dipteran genomics, immune gene characterisation, and evolutionary analyses of vector competence-associated genes. RESULTS: A 129.5 Mb genome was assembled into three chromosomes with high contiguity (N50 = 43 Mb, L50 = 2) and high completeness (98% for Arthropoda BUSCO odb10 lineage). Genome annotation identified 11,708 genes, including 661 immunity-related genes, as well as genes associated with key functional categories such as metabolism, sensory perception, and host-pathogen interactions. Comparative gene family analyses across 12 dipteran genomes revealed strong family-level (Ceratopogonidae) and genus-level (Culicoides) evolutionary signatures. In C. brevitarsis, 405 expanded and 262 contracted gene families were enriched for functions associated with metabolism, regulation, locomotion, and stimulus response. Integration of transcriptomic datasets from C. sonorensis Wirth and Jones identified 82 orthologous genes in C. brevitarsis corresponding to genes previously associated with differential responses to bluetongue virus infection, including lineage-specific patterns of conservation and selection. CONCLUSIONS: The genome provides a foundational resource to understand the molecular biology and evolutionary features of C. brevitarsis. Integration of immune, sensory, metabolic, and evolutionary analysis provides a framework for future functional and comparative studies aimed at understanding variation in arbovirus transmission among Culicoides species.