I20 



Journal of Agricultural Research 



Vol. IV, No. 2 



account of the physiological disturbance and i female moth emerged. 

 Figure 4 gives the deaths among the 20 caterpillars fed with the unfil- 

 tered material. Of these 17 died of wilt, and 3 of the "other cause." 

 Figure 5 shows the deaths among the 15 control insects that accom- 

 panied the caterpillars fed with the unfiltered virus. All 15 died of the 

 "other cause." Table II gives the results of this series of experiments. 



Table II. — Mortality among gipsy-motk caterpillars in laboratory experiments {series i) 



«■ Escaped. 



It will be seen that there are almost three times as 

 many deaths from the unfiltered virus as from the 

 Berkefeld filtrate. This shows that the wilt virus is 

 filterable, but with difficulty. Although it would have 

 been much more encouraging to have obtained moths 

 from all the controls, still it is very significant that not a 

 single control insect died of wilt. Noteworthy, also, are 

 the four female moths obtained from the animals fed 

 with the Berkefeld filtrate. 



No difference was noted in the rate 

 of deaths between caterpillars fed 

 with the I to 25 dilution and those 

 fed with the i to 50 dilution. 



While the caterpillars in the 

 foregoing experiments were those 

 used in the actual experiments in 

 this laboratory, there were, never- 

 theless, other caterpillars in trays in the same room. 

 These were held in reserv^e as stock, but, since not 

 a single one of them died of wilt, they may be 

 regarded also as controls against the experiments, 

 for they were all placed in the trays on the same fig. 5.— curve showing 

 day the tests were begun (June 18). They were not the mortality among the 



IS control gipsy-moth 



Fig. 4. — Curve show- 

 ing the mortality 

 among 2ogipsy-moth 

 caterpillars fed with 

 unfiltered wilt virus. 



caterpillars, 

 with figure 4. 



Compare 



all the same age, however, and, hence, can not be 

 called controls in the strictest sense of the word. 



Figure 6 gives the mortality among 15 second-stage and third-stage 

 caterpillars. Three were placed in each tray, and all 15 died of the 

 "other cause." 



