Abstract Tipula iridescent virus was inoculated into healthy Galleria mellonella larvae as well as into larvae which received 5, 10, 20, and 50 Kr of gamma radiation. Cytopathological studies of larvae exposed to 5 Kr showed that most of the tissues were susceptible to TIV attack. The tissues of the larvae receiving 10 Kr were not attacked by TIV in the first week following irradiation. However, scattered TIV particles appeared in the midgut (MG) epithelium, circular visceral muscles (CVM), longitudinal visceral muscles (LVM), and skeletal muscles (SKM) in the second week. TIV was not observed in adipose tissues (FB), ventral nerve cord (VNC), Malpighian tubules (MPGT), and tracheal matrix (TRMX) up to the end of the second week. When the radiation dose was increased to 20 Kr, there was a change in the susceptibility of irradiated tissues to TIV attack. In the first week, even those tissues which were not infected by TIV in larvae exposed to 10 Kr group, such as TRMX, MPGT, and FB, appeared to be infected by scattered TIV particles. The scattered TIV particles in these tissues were rare in the second week. However, the CVM, LVM, SKM, VNC, and hypodermis showed an increased number of TIV particles at the end of second week. The pattern of inhibited development of TIV in 50 Kr group was nearly similar to that of the 20 Kr group, and in all cases appeared to be correlated with the appearance of vacuoles and spaces in the cells. Perhaps the permeability of the irradiated cells may be a factor in determining the attack of insect viruses on such cells.