October, '22] warren: moisture and boll weevil poisoning 



347 



weevils feeding in the presence of dew were removed in the morning 

 (after feeding during the night) to fresh unpoisoned plants and those 

 feeding in the absence of dew were removed (after feeding during the 

 day) to fresh unpoisoned plants and mortality records were kept. In 

 each case for comparison, check cages were run on unpoisoned plants. 

 This should give an accurate and critical test of the role of dew in poison 

 ingestion by the weevil. The only inaccuracy which enters in is the 

 fact that those weevils feeding in the absence of dew have only a feeding 

 period of 10 hours against 14 hours for those feeding in the presence 

 of dew but it will be seen that this did not affect the results. It may 

 not seem fair to compare night feeding with day feeding but if we assume 

 that dew is necessary for the ingestion of the poison, this is the period 

 in which the weevil has an opportunity to drink the dew. In each case 

 the weevils were placed on the caged plant a few hours before applying 

 the poison in order to allow them to adjust themselves to the plant. 

 Cages of the size 3x3x4 feet were used in these experiments. The re- 

 sults of these experiments are given in table I. 



Table I. 



A record was kept of the mortality for 72 hours after the poison had 

 been applied, the first 10 or 14 hours of which were spent on the poisoned 

 plant by the weevil. It will be seen from the table that there was a great- 

 er mortality (45%) among the weevils which fed during the period in 

 which there was no dew on the plant although they remained on the 

 poisoned plant a much shorter period than did the weevils feeding 

 in the presence of dew (mortality 35%). The results given in table 

 I were for the season 1920 and to further check the results the experi- 

 ment was repeated in 1921 under more carefully controlled conditions. 



It was found during the summer of 1920 that there was considerable 

 difference in natural mortality among collections of weevils made in 

 different fields or at different periods in the same field. It is probable 

 at the late season when these experiments were conducted, there was 

 considerable overlapping of broods so that, from one collection one 

 might obtain only newly emerged weevils in which the natural mortality 

 would be low, while from a nearby field one might obtain comparatively 



