The rate of development in flour and grain, adult longevity and female fecundity of a strain of Rhyzopetrtha dominica (Fabricius) were measured under constant conditions of temperature and relative humidity. The time required for the development of adults from eggs was 36.3 ± 0.4 days in flour and 32.4 ± 0.4 days in grain. Adult females lived 50 .9 ± 3. 8 days and laid 119 ± 2 3. 8 eggs during this time. The mean longevity of males was 42.1 ± 2.8 days. The rate of increase per generation of R. dominica was 30. 2 in flour and 30. 8 in grain based on data on total longevity, fecundity and mortality during immature development. Susceptibilities of the different life stages of R. dominica to ionizing radiation were determined. The immature insect's response to killing by radiation varied among the metamorphic stages. The pupa was more resistant than either the egg or larva. The eggs irradiated with 0. 8 krad produced more adults than the untreated eggs. Judging from the mortality of irradiated adults and of the adults developing from the irradiated immature stages, the _eggs and larvae were most susceptible. The pupae were more resistant than the larvae at both LD50 and LD99 levels; the adult was more resistant than the pupa at LD99 level but less resistant to radiation than the pupa at the LD50 level. The data on progeny produced by the irradiated adults and by the adults developing from the irradiated eggs, larvae and pupae indicate that all metamorphic stages were equally affected by radiation. From reciprocal crossings of irradiated and non-irradiated male and female adults, it was found that females were more radioresistant than males in terms of egg hatchability score. Under the experimental conditions used the dose of 16.0 krad, which has been recommended for disinfestation, can be expected to completely inhibit reproduction of R. dominica adults but may allow the production a few adult progeny by adults developing from pupae in the F1 generation. The factors likely to be encountered in commercial usage with an industrial irradiation unit are discussed and an explanation offered as to how these might actually enhance the efficacy of the recommended dose level.