122 



Journal of Agricultural Research 



Vol. IV, No. 2 



lo females and 23 males emerged. Figure 12 gives the deaths among 

 25 caterpillars fed with the unfiltered virus. Twelve died of wilt while 

 caterpillars and four after pupating; three died of the "other cause; " and 

 six male moths emerged. Figure 13 shows the mortality among 25 con- 

 trols accompanying the series. Three died of wilt, seven died of the 

 "other cause," and twelve males and three females emerged. Table III 

 gives the results of series 2. 



Table III. — Mortality amouj gibsy-vioth caterpillars in laboratory experiments 



(series 2) 



It will again be noticed that more caterpillars died when 

 fed with the unfiltered material than when fed with the 

 Berkefeld filtrate. If there had been as many caterpillars 

 in the experiments with the unfiltered material as in the 

 Berkefeld-filtrate experiment, the number of deaths from 

 wilt in the former would probably have been more 

 than twice as great as in the latter. Three deaths from 

 wilt are recorded in the controls, but these caterpillars had 

 probably contracted the disease before 

 they were collected, as every possible 

 precaution was taken to avoid contami- 

 nation. The person who fed the in- 

 fected individuals was not permitted to 

 feed the controls and whenever a cater- 

 pillar died and had to be handled, the 

 hands of the assistant were thoroughly 

 washed in 95 per cent alcohol before be- 

 ing again allowed to handle another 

 tray. In this series of experiments 

 there seems to be no correlation between 

 high temperatures and deaths due to 



wilt. Taking the middle of the temperature range 



in the entire series, there are 31 deaths below 79.5° 



against 2 deaths above 79.5° F. Humidity might 



prove to be a more important or at least an equally im- 

 portant factor as temperature in determining the progress of the disease ; 



but, since no record was kept of the humidity, the writer is unable to 



speak with any conviction on this matter. 



Fig. 8.— C u r V e 

 showing the 

 mortality 

 among 8 "con- 

 trol" fourth- 

 stage gipsy- 

 moth cater- 

 pillars from 

 Providence , 

 R. I. 



Fig. 9. — Curve showing 

 the mortality among i6 

 "control" fifth-stage 

 gipsy-moth caterpillars. 



