Taxonomy and molecular phylogeny of a new species of black fly (Diptera: Simuliidae) in the <i>Simulium striatum</i> species-group from central Thailand

Generally, the DNA barcode relying on a short fragment of the cytochrome c oxidase I (COI) gene is a powerful tool for facilitating species discovery and taxonomic resolution in Diptera, including black flies. However, the COI barcode lacks sufficient resolution to identify several species or infer phylogenetic relationships of black flies in the Simulium striatum species-group, whereas the fast-evolving nuclear big zinc finger (BZF) gene has been suggested as a key marker for identifying the species. In this study, a new species of black fly in the S. striatum species-group from Kamphaeng Phet province, central Thailand, was discovered and characterized through an integrated method combining morphological analysis and molecular data based on the BZF gene. The new species, Simulium (Simulium) concitatum sp. nov., was morphologically described for all life stages, excluding the egg. It shares many morphological similarities with other species of the S. striatum species-group, particularly S. thilorsuense Takaoka, Srisuka & Saeung, 2022 described from Tak province, western Thailand. Sequence analysis and phylogeny inferred from the BZF gene further confirmed that S. concitatum sp. nov. is a distinct species of the S. striatum species-group and revealed its close genetic relationship to S. wangkwaiense Takaoka, Srisuka & Saeung, 2020. The morphological differences between the new species and all known species of the S. striatum species-group documented in Thailand and other countries are provided to assist in species identification. Furthermore, this study underscores the BZF gene as an effective genetic marker to differentiate the species.