June 12. 1916 Effect of Rontgen Rays on Tobacco Beetle 387 



In these experiments the larvae hatched from treated eggs failed to 

 develop. In several other series of experiments with Rontgen rays made 

 by the writer and also in experiments made by Morgan and the writer/ 

 eggs given lighter dosage hatched and development seemed normal, 

 several generations of tobacco beetles being reared from some of the 

 tobacco and cigars which contained treated eggs. 



In the two experiments with larvae (No. 19 and 20), no immediate 

 effect as the result of exposure to the rays was noted. After a time the 

 larvae became inactive, somewhat shrunken, and changed in color, and 

 no evidence of feeding could be observed. Nearly all remained in an 

 inactive or dormant condition for long periods before death. Two larvse 

 exposed on June 7 (experiment 20) remained alive until January 10, 19 16. 

 All check larvae used in this experiment had transformed to the adult 

 stage by July 11. All treated larvae died before reaching the pupal 

 stage. With conditions under which the material used in the experi- 

 ments was kept, the normal larval period of the tobacco beetle is about 

 40 days. All larvae used in the experiments were partly grown when the 

 experiment was made. No further growth could be noticed. In general, 

 the effect of the heavy exposure given (600 milliampere minutes, voltage 

 65,000, distance from focal spot of Rontgen tube 7.5 inches) seems to 

 have been to stop development and activity and to produce an inactive 

 or dormant condition, and greatly to prolong the larval period. 



The results of all previous experiments with larvae given comparatively 

 light exposures had shown entirely negative results. 



In the experiment with pupae (experiment 21) the number of pupae 

 used was not sufficiently large to permit the drawing of positive con- 

 clusions. Of the 20 specimens treated, only 4 reached the adult stage. 

 These seemed normal, but died without laying eggs. 



In the two experiments with adults (experiments 22 and 23), the 

 results obtained were very similar. The exposure given apparently did 

 not affect the length of life or the activity. Mating was observ^ed and 

 large numbers of eggs were laid. None of the eggs from the exposed 

 beetles hatched, while eggs from the check beetles hatched normally. 



Egg clusters of the tent caterpillar (Malacosoma americana Fabricius) 

 and the white-marked tussock moth (Noiolophus leticostigma Smith and 

 Abbot) were used. With both of these species the period of incubation 

 is very long, eggs deposited in summer or fall not hatching until the 

 following season. An exposure of 150 milliampere minutes was given. 

 Other conditions of the experiment were the same as in experiment 7 

 made with eggs of the tobacco beetle, details of which are given in 

 Table I. The experiment was made on April 16. The egg clusters 

 treated contained something over 1,000 eggs of each species. The same 

 number of clusters were kept as checks. Both experiments gave nega- 



' Morgan, A. C, and Runner, G. A. Some experiments with Rontgen rays upon the cigarette beetle 

 l,asioderma serricome Fabr. /» Jour. Econ. Ent., v. 6, no. 2, p. 226-230. 191J. 



