386 Journal of Agricultural Research voi.vi.No.it 



EXPERIMENTAL WORK 



Eggs for the experiments were obtained by placing large numbers of 

 tobacco beetles in jars containing leaf tobacco which had been sterilized 

 by heat. The eggs were then placed between slabs of chewing tobacco 

 in wooden boxes. The covers of the boxes were tightly sealed with 

 adhesive tape. Control boxes containing approximately the same 

 number of eggs as the treated boxes were prepared in a similar manner- 

 Infested tobacco containing larvae, pupae, and adults was also exposed 

 in sealed wooden boxes. After exposure the insects were transferred to 

 wooden boxes containing granulated tobacco which had been sterilized 

 by heat, A corresponding number of specimens were kept as controls. 



Exposure to the rays was made by placing the containers directly 

 under the Rontgen tube at a distance of 7.5 inches from its focal spot. 

 In order to guard against any efifect of heat, a fan was kept blowing on 

 the container while the exposure was made. The maximum temperature 

 registered by a thermometer placed in the chamber was 91° F. 



In the series of experiments tabulated 150 milliampere minutes (current 

 of 15 milliamperes for 10 minutes or a current of 10 milliamperes for 15 

 minutes), with a voltage of 65,000, was the minimum dosage applied. 



The material used in the experiments was kept under observation until 

 January 10, 191 6. Table I gives the details of the experiments. The 

 notes included show the condition at different times. During the colder 

 months the material was kept in an automatically regulated electric 

 incubator in which suitable breeding conditions were maintained. The 

 temperature was kept at 86° F. and the humidity at 80. 



Eggs from exposed beetles were kept under daily observation. Part 

 were kept in cells on microscope slides and part were kept on the leaf 

 tobacco on which they were laid and placed between slabs of chewing 

 tobacco. Most of the eggs which failed to hatch became shrunken and 

 changed in color in about 10 days. Part remained plump and apparently 

 normal for a considerable time. In eggs which were over 2 days old 

 and in which embryonic development was well advanced when treated 

 the partly developed larvae could be seen within by examination with a 

 microscope. 



As will be seen in Table I (experiments 11, 14, and 18), hatching took 

 place in some of the eggs which were over 3 days old. In experiment 14, 

 which was made with eggs nearly hatched when treated, part of the 

 eggs hatched, even though the dosage of 150 milliampere minutes, which 

 was effective with the newly laid eggs, had been increased to 600 milli- 

 ampere minutes. 



Results of previous experiments, as well as those tabulated, indicate 

 that in treatment of the egg stage heavier dosages are required to sterilize 

 eggs which are nearing the end of the incubation period than are required 

 to sterilize eggs newly laid. 



