Acute lethality in irradiated flour beetles: Evidence against a role of bacterial infection

Abstract

The time course of mortality and the mean survival time of flour beetles dying after X-irradiation varied slightly in different strains and species. Within a given strain, however, both minimum and mean survival time were independent of dose over a wide range of exposures and independent of percent mortality. These findings suggest the operation of a single mode of death in irradiated beetles, in contrast to the “hierarchy of modes of death” recognized in irradiated mammals. Invasion of blood and tissues by enteric bacteria which gain entrance through the damaged intestinal lining, and subsequent spread of such infection, have been implicated in the lethal syndrome of irradiated mammals. The present investigation indicates that bacterial invasion does not contribute to the death of irradiated beetles. This conclusion is based on the lack of influence on survival of (1) administration of neomycin at levels which eliminated virtually all bacteria from the insects, (2) crowding or isolation, or (3) maintenance of irradiated beetles on medium in which other beetles previously had been raised. In addition, analysis of the distribution of deaths among a large number of vials each containing a small number of beetles disclosed no deviation from expectation based on random distribution; thus it seems unlikely that there is any “spread” of contagion within vials.