Objective   In order to clarify the species and structure differences of bacteria in the gut, Malpighia's duct and ovary of the Chrysops. vanderwulpi.

  Methods  C. vanderwulpi was captured near a cattle farm in Daqing city, Heilongjiang province. The 16S V3-V4 region of the midgut, Malpighenian duct and ovary of 25 C. vanderwulpi flies was detected and analyzed, and the bacteria were isolated and cultured.

  Results  A total of 1331 OTUs were obtained, with 1211, 1204 and 1257 OTUs in the midgut, Malpigsian tubule and ovary, respectively, of which 1051 OUTs were shared by all three samples. At the phylum level of the three sites, Firmicutes, Proteobacteria, and Bacteroidetes were the most abundant, totaling more than 80.00%. At the genus level, the composition of bacteria in different parts was different. The relative abundance of Lachnospiraceae was the highest in the midgut, accounting for 8.38% of the total content of bacteria. The relative abundance of Lactobacillus was the highest in Malwinia tubule, accounting for 12.13% of the total content of bacteria. Enterobacter was the most abundant genus in the ovary, accounting for 10.60% of the total flora. Blast analysis of all sequences showed that some sequences were similar to those of the pathogenic bacteria Metamycoplasma hominis, (CP055150), Paeniclostridium sordellii, (MT539084) , Haemophilus parainfluenzae (LT674777), Plesiomonas shigelloides (MT57312), Paraburkholderia terrae (MN150518), Ureaplasma parvum (CP041199), Helicobacter cinaedi, Paraburkholderia terrae (MF440359) were 100.00% homology. In the culture results, 37 strains, 5 genera and 9 species were cultured under aerobic condition, while 20 strains, 6 genera and 7 species were cultured under anaerobic condition, and no pathogenic bacteria were cultured. Conclusion In this study, the bacterial diversity of Tabanus was analyzed for the first time, and the composition and differences of bacteria in the gut, Malpiglet's midduct and ovary of C. vanderwulpi were analyzed. A variety of potential pathogens have been detected in the Horseflies, and some bacteria were isolated and identified, but no pathogenic bacteria were cultured. The results provide reliable data for the further study of the flies and the diseases transmitted by them.