358 Illinois State Ldboratoinj of JSatural History. 



disease were broken in pieces and thrown about in the 

 box, and numbers of young chinch-bugs were introduced. 

 In a few days some dead insects were found, but after 

 a time the disease seemed to die out. Most of the 

 insects were reaching the pupa state, and experiments 

 were discontinued until the bugs reached the adult con- 

 dition. 



When the adult bugs became abundant, Mr. W. G. 

 Johnson, an Entomological Assistant in the Laboratory, 

 conducted several infection-box experiments with various 

 diseases, and in one of these the bacillus of the squash- 

 bug disease was used. Every effort was made to get the 

 bugs infected, and they were thoroughly wet with the 

 spray of infusions rich with the bacillus direct from fresh 

 pure cultures. Very few bugs died in this box; indeed, 

 no more than died in other boxes with other diseases,, 

 and apparently no more than in the check box. The 

 failure of these experiments with adult chinch-bugs, and 

 on a scale so much larger than the tumbler experiments 

 which I had previoush' concluded, somewhat chilled the 

 prospect of pushing field experiments. 



It was now- necessary to test the organism on adult 

 chinch-bugs under the conditions prevailing in the ex- 

 periments given in Tables 11. and III., in order to 

 compare by actual count the death rate of the old bugs 

 with that of the young. In this instance two tumblers 

 were employed for each experiment. The sand in both 

 jars was very slightly moist at the beginning; but in 

 one it was allowed to dry out gradually, while in the 

 other it was kept moist. As before, about five hundred 

 bugs were used in each tumbler. The bugs were brought 

 from the field in quantity, and as some appeared to be 

 stifled, all dead bugs were removed from each of the 

 cages after twenty-four hours, in order to avoid any 

 error from outside sources. When infusions are men- 

 tioned, temporary immersion of the insects to secure 

 infection must be understood. The following table gives 

 all essential data. 



