POISONING COTTON-BOLL WEEVILS. 



11 



results in the field. These were conducted under cage conditions and 

 were for the purpose of comparing the effectiveness of different 

 poisons and different methods of poisoning. 



IMPORTANCE OF MOISTURE IN POISONING. 



One interesting feature of the foregoing tests was the apparent 

 necessity of the presence of moisture if any considerable degree of 

 weevil mortality were to be caused by the poison. It was found that 

 only a very light mortality would result from tests where the plants 

 were kept absolutely dry after poisoning; but as soon as moisture 

 was introduced the mortality increased tremendously. This evi- 



Fig. 8. — View down center of poisoned plat, Isola Cut No. 1, on October 26, 1917, showing cotton availal le 

 for second picking; Scott, Miss. For comparison with figure 7. 



dently validated the conclusion that at least a major portion of the 

 success in poisoning was due to ingestion by the weevil while drinking. 



RELATIVE EFFECTIVENESS OF DIFFERENT ARSENICALS. 



In the course of these experiments quite a number of different 

 poisons were utilized and it was found that nearly all arsenicals 

 were effective to a certain degree but that most of them were not 

 sufficiently effective to be satisfactory. At the outset the ordinary 

 triplumbic form of lead arsenate was utilized. It was found, how- 

 ever, that this was not sufficiently toxic to the weevils to warrant 

 its use and the newer dihydrogen form of lead arsenate proved to be 

 vastly more toxic. This was utilized in practically all of the experi- 

 ments of 1916, but additional tests demonstrated that a high grade 



