Abstract: Many genera were erected without phylogenetic validation in Bittacidae, a cosmopolitan family in Mecoptera, leaving their generic statuses contentious. Here, we investigated the phylogenetic relationships and reconstructed the ancestral states of chromosome numbers and key morphological characters for 26 species in three genera of Bittacidae using an integrative approach combining molecular, cytogenetic, and morphological data. The phylogenetic analyses reveal that all three genera studied are paraphyletic, but cytogenetic evidence supports the generic status of Terrobittacus Tan & Hua with haploid chromosome numbers ≥20. In contrast, the genus Bittacus Latreille, 1805 exhibits an extensive chromosomal variation from n = 8 to n = 22. Ancestral state reconstruction suggests that the diagnostic character of Bicaubittacus Tan & Hua may represent an apomorphy restricted to a few species. The cytogenetic investigation indicates that n = 22 was the ancestral chromosome number in Bittacidae. Chromosome fusions were likely responsible for numerical reduction in chromosomes of Terrobittacus, whereas more complex structural and numerical variations accounted for the chromosome diversity of Bittacus and Bicaubittacus. To satisfactorily resolve the generic problem of Bittacidae, taxon sampling should be greatly expanded at the global scale, and more attention should be paid to the integrative taxonomy.

Key words: Bicaubittacus, Bittacus, chromosome, hangingfly, karyotype, phylogeny, Terrobittacus.