Diptera even though is one of the most ecologically significant and species-rich insect orders, there are still unresolved phylogenetic relationships among its basal lineages, particularly within the infraoder Blephariceromorpha, due to limited molecular data. To address this gap, this study employs two parallel genomic approaches: mitochondrial genomes and nuclear genomic analysis, covering 64 families and over 100 species of Diptera and their outgroups, to elucidate these phylogenetic relationships. Our results strongly support the monophyly of each constituent family (Blephariceridae, Deuterophlebiidae, and Nymphomyiidae), yet they reject the monophyly of Blephariceromorpha. Crucially, we found that Deuterophlebiidae and Nymphomyiidae form a sister group as the basal-most lineage of Diptera, whereas Blephariceridae is positioned within Psychodomorpha. This indicates that the similar larval habitats and morphological traits shared between Blephariceridae and the combined group of Nymphomyiidae + Deuterophlebiidae are the results of convergent evolution. By resolving long-standing debates on the relationships within Blephariceromorpha and the basal lineages of Diptera, this study provides new insights into the evolutionary history of Diptera, especially within the suborder Nematocera.

Animal systematics and taxonomy; Diptera; Evolutionary ecology; Mitogenomes; Nematocera.