Effects of γ radiation on the reproduction and enteroendocrine cells of the spruce bark beetle Ips typographus and prospects for its control

The European spruce bark beetle Ips typographus is one of the most important pests of spruce forests in Europe. The present study investigated the feasibility of a sterile insect technique (SIT) for this pest control. Laboratory-reared males were exposed to various doses of γ radiation (0, 10, 30, 50, 70 and 90 Gy) and allowed to mate with laboratory-reared untreated females. The radiation significantly affected the number of viable offspring. Although females oviposited on average 16.0–18.8 eggs per maternal tunnel in all treatments, the number of larval tunnels per maternal tunnel observed after 4 weeks of development decreased from 17.3 in the control (0 Gy) to 4.5 in the 90-Gy group. Numerous oviposition sites without larval tunnels were observed in galleries when males received high doses (70 and 90 Gy) of γ radiation. Comparison of the sperm viability in the control and irradiated males did not reveal any statistically significant differences. Side effects of the irradiation were examined by immunostaining of the enteroendocrine cells. Two distinct types of cells were revealed with antibodies to neuropeptides allatostatin A and tachykinin in the midgut. The alimentary tracts of males receiving a high dose of radiation (90 Gy) showed a significantly decreased number of tachykinin-like immunoreactive enteroendocrine cells. This observation suggests potential radiation-induced damage of the digestive system, which could lead to a reduction in male fitness. The implications of these findings for successful use of SIT in spruce bark beetle control are discussed.