The influence of pupal age on sensitivity to radiation.

In recent years there has been increasing interest in the application of ionizing radiations in the control of insects, and increasing recognition of the usefulness of insects as experimental subjects in the investigation of radiobiological phenomena. For sdme types of radiobiological study, the germicidal wave-lengths of ultraviolet (UV) radiation, since they are preferentially absorbed by nucleic acids, may be employed more advantageously than the ionizing wave-lengths of x- and gamma radiations. Furthermore, sources of UV radiation are inexpensive, relatively non-hazardous, and readily available. Unfortunately, interpretation of the effects of UV on metazoa may be complicated by the fact that the radiation penetrates only a few cell layers; this explains the paucity of data on UV effects on insects, except for those on insect eggs. As part of a more extensive investigation of recovery mechanisms in irradiated Tribolium (Ducoff and Walburg, 1960; Ducoff and Bosma, 1963) we have compared the effects of x-rays and germicidal UV on pupal stages of T. confusum. The two types of radiation differed markedly in regard to stage of greatest sensitivity and to the relative importance of lethal effects and induction of developmental abnormalities. MATERIALS AND METHODS The T. confusum stock employed was derived from the colony of G. Fraenkel; the beetles were maintained in white flour supplemented (4%o) with brewer's yeast, at 30? C. and 70% R. H. Individual cultures were kept in previously washed polystyrene vials fitted with perforated snap-caps. X-irradiation was performed with a Picker Vanguard deep-therapy machine, operated at 280 kvp and 20 ma; HVL was 1.0 mm. copper, and subject-target distance was 40 cm., yielding a dose rate of approximately 250 r/min., as measured with a Victoreen condenser meter. The UV source was a 15-watt germicidal lamp in a desk-type fluorescent fixture; this gave intensities of about 250 ergs/mm.2/min. at a distance of 100 cm. The output of this type of lamp declines with use, so actual dose rate was measured at the end of each exposure series, using a General Electric Ultraviolet Intensity meter. Care was taken to avoid photoreactivation.