[Objectives]  To investigate the effect of the fungus Ophiocordyceps sinensis (a unique and valuable parasitic complex formed by the infection and subsequent mummification of Thitarodes larvae by O. sinensis) and insect hormones on the blastospore-hypha conversion in Thitarodes larvae (the formation of hyphae from the blastospores of O. sinensis in the hemolymph of Thitarodes larvae is a prerequisite for the mummification of infected larvae). [Methods]  One of five treatments; blastospores of O. sinensis (KD strain), a mixture of blastospores and 20-hydroxyecdysone (KD+20E), a mixture of blastospores and methoprene (KD+M), 20-hydroxyecdysone (20E) or Methoprene, were injected into sixth instar T. xiaojinensis larvae and the subsequent larval mummification rate, hemolymph and intestinal microorganisms and amounts of related substances (farnesol, ergosterol, ecdysterone, juvenile hormone III, N-acetylglucosamine, glucose, trehalose, nitric oxide) in larval hemolymph were compared. [Results]  The mixture of blastospores and methoprene significantly increased the mummification rate of larvae after 120 days. More bacterial species were isolated from larval hemolymph injected with KD+20E, whereas more fungi were isolated from larvae injected with KD+M. Three bacterial species including Pseudomonas mucidolens, Serratia proteamaculans and Tsukammurella standjordii, were detected in all treatments, except for the absence of T. standjordii in the hemolymph of larvae injected with Methoprene. Cladosporium sp., Isaria farinosa and Talaromyces sp. were the most frequently observed fungal species, none of which were found in the hemolymph of larvae that had not been injected. Seven bacterial species, including Carnobacterium maltaromaticum, Flavobacterium frigidimaris, Microbacterium oxydans, P. mucidolens, Rahnella aquatilis, S. proteamaculans and T. strandjordii, as well as one fungal species, Apiotrichum porosum were detected in the guts of all treated larvae. C. maltaromaticum was the dominant bacterial species found in larval guts. The injection of KD+M increased the culturable fungal species in larval guts. The most common fungal species were I. farinosa and Penicillium sp., whereas O. sinensis was not isolated from larval guts. Compared to the control (PBS) group, the injection of blastospores of O. sinensis and insect hormones did not significantly change the levels of farnesol, 20E, trehalose and nitric oxide, but injection of the KD, KD+20E, KD+M, 20E and M increased the amount of juvenile hormone in larval hemolymph after 45 days. N-acetylglucosamine was absent in the hemolymph of larvae that were not injected or that had been injected with KD+20E. Tyrosol was not detected in the hemolymph of larvae irrespective of the presence or absence of O. sinensis blastospores. [Conclusion]  The mummification rate, hemolymph, intestinal microorganisms and levels of related substances in the hemolymph, of T. xiaojinensis larvae were all affected by injecting them with blastospores of O. sinensis, 20-hydroxyecdysone or Methoprene. These results provide useful insights for improving the larval mummification rate during artificial cultivation of O. sinensis, and improve understanding of the interactions between insects and fungal pathogens.