Abstract:  【Aim】 Chromosomal characteristics play significant roles in phylogenetic analyses of insects. However, chromosomes in Bittacidae (Mecoptera) have rarely been studied to date. 【Methods】 Larvae, pupae and adults of the hangingfly Bittacus flavidus Huang & Hua were obtained by rearing in the laboratory. Chromosome preparations for the testes of the last (4th) instar larvae, pupae and newly-emerged adults of the hangingfly were stained with 4′,6-diamidino-2-phenylindole (DAPI) to investigate the karyotype, meiotic behavior, and sex determination. 【Results】 The results showed that the chromosome number of B. flavidus is 2n=26+X0, and all the chromosomes are metacentric, showing a symmetric karyotype. The absolute length of bivalents ranged from 3.20±0.07 to 1.53±0.19 μm, and the relative length from 5.31±0.29 to 2.73±0.24, with their size decreasing gradually from pair to pair. The meiosis of B. flavidus is chiasmate with a mean chiasma frequency of 11.5 per nucleus and a mean chiasma frequency of 0.88 per autosomal bivalent. The sex determination mechanism is of the XX/X0 type. Fluorescent bands with DAPI staining revealed a large AT-rich block covering one terminal region on all pachytene bivalents. 【Conclusion】 The chromosomes exhibit marked variations with respect to the diploid number, fundamental number and karyotype formula, suggesting that chromosome rearrangements (especially fusion, fission and inversion) play an important part in the lineage differentiation and chromosome evolution in Bittacidae.

Key words: Bittacidae, cytogenetics, karyotype, sex determination mechanism, meiosis, phylogeny