The general pattern of the time course of survival of Tribolium castaneum larvae, irradiated at different ages (from 2 to 17 days old), was similar when exposures from 2.0 to 5.0 kR were used. Mortality during the larval stage was rare, but mortality between pupation and a time shortly after eclosion was frequent. Young larvae were less radiosensitive than old larvae. The${\rm LD}_{50(60)}$ for 2-, 7-, 12-, and 17-day-old larvae, maintained at 30°C, were 4.95, 4.30, 3.20, and 3.20 kR, respectively, at an exposure rate 230 R/minute. When the exposure rate changed from 230 to 1250 R/minute, mortality was slightly increased. The${\rm LD}_{50(100)}$ of 14-day-old larvae, kept at 22°C postirradiation, was similar to the${\rm LD}_{50(60)}$ of 14-day-old larvae kept at 30°C. Larvae kept at 15°C for 12 hours before and after irradiation and for 24 hours postirradiation exhibited no significant change of response, as compared to untreated larvae. Exposure of larvae to 15°C for 24 hours prior to irradiation, however, showed a slight increase of radiosensitivity.

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