The Effect of Gamma Radiation on the Fertility and Longevity Of Dolichoderus Quadripunctatus (Hymenoptera: Formicoidea Dolichoderidae)

The authors studied on a batch of 27 colonies of the ant Dolichoderus quadripunctatus the effect on longevity and fertility of gamma irradiation at doses between 12 500 and 150 000 rad. The results are presented in the paper. For colonies consisting solely of workers, the mortality curve is linear with doses between 150 000 and 50 000 rad. The LD50 is reached in 4 days for the 150 000-rad dose and 16 days for the 50 000-rad dose. The lowest dose used in the experiments (12 500 rad) produced an LD50 after 18 days. For the control colonies, the LD50 occurred within about thirty days. Fertility, which is normally regular and constant in colonies of workers of Dolichoderus quadripunctatus is expressed by the R.F. ratio [R.F. - reproduction factor = (number of eggs number of workers at the beginning of the experiment)]. The R. F. of the control (unirradiated) colonies was about 1.60, while that of the irradiated colonies ranged from 0 to 0,06. These extremely low values showed that to all intents and purposes the treated colonies were made sterile. This sterility was final, no laying being observed in the irradiated colonies, by the time they died out. In colonies with a queen, only the queens were irradiated, with gamma doses of 50 000, 100 000. and 150 000 rad. The results obtained for longevity showed in every case a considerably higher resistance of the females than the workers under the same conditions. Where fertility is concerned, the irradiated females showed a considerable and almost immediate reduction in egg laying. This was followed in the colonies by a resumption of laying by the workers, since the queen could no longer inhibit this. The fertility of the irradiated females subsequently diminished, and became nil from the eighteenth day. The queens did not thereafter resume laying. (author)