Abstract
The purpose of this study was to clarify the changes in ultraviolet sensitivities to killing during the instar stage. When larvae were exposed to ultraviolet light, with a dose of 7×104ergs/mm2, at various stages from hatching to the end of the third instar, a pronounced cyclic change in radiosensitivity to killing was observed during each instar. The most sensitive stage for killing was when about 60 percent of the age of each instar was reached, corresponding to the late DNA synthetic period in the epidermal cells which are presumed as the critical organ. Furtheremore, it was confirmed that the killing effect of ultraviolet light was photoreactivable to a certain extent. Possible mechanisms behind the phenomena of such killings have been discussed.
