75 



weevil derives its food from deep punctures, thus ingesting very little 

 of the poisoned external plant tissues. Studies on the boll weevil 

 under cage -conditions during 1913 and 1914 showed that water was 

 essential to its continued existence, and from this fact was derived 

 the idea of poisoning the water which the weevils would drink. 



The first tests of this nature were begun in 1915 in typical delta 

 territory normally subject to very heavy weevil injury owing to the 

 prevaihng great humidity and excessive rainfall. Three series of 5 one- 

 acre plots were taken, the two end ones of each series being given 4, 5, 

 and 6 apphcations of dry dust poison respectively. The results showed 

 that every poisoned plot yielded more than the untreated controls, 

 the most pronomiced feature being the greater increase in yield with 

 the larger number of poisonings. Thus with 4 applications a gain of 

 about 15 per cent, was secured ; \nth 5, this gain was increased to 

 about 35 per cent., while 6 apphcations increased it to 70 per cent. 

 As all apphcations were begun at the same time and the extra ones 

 simply meant the continuation of the treatment until later in the 

 season, the importance of late season apphcations seemed obvious. 



In 1916 similar experiments were carried out, beginning with the 

 first appearance of the weevils in June and lasting until about the 

 1st September, the results being quite as definite as those of 1915 and 

 very plainly demonstrating the greater importance of late-season 

 applications. 



In 1917 it was intended to conduct an elaborate series of tests to 

 study the comparative efficacy of different poisons, the time of day 

 when apphcation gave the best results, the most profitable season 

 of apphcation, the proper interval between apphcations, the requisite 

 amount of poison per acre and many other similar questions. 

 Unfortunately, however, the season was most remarkable for the 

 shght amount of weevil damage and the experiments had to be given 

 up. About the middle of August experiments on a large scale were 

 rendered possible in an adjacent State, where late planting and adverse 

 weather conditions had combined to produce an exceptionally heavy 

 weevil infestation. It was too late to attempt to set a new crop by 

 poisoning, but an effort was made to save the bolls then present on 

 the plants. One application of poison was given, and 10 days later 

 it was found that the number of punctured squares had been reduced 

 from 86 per cent, to 36 per cent., thus showing poisoning to be a very 

 profitable operation. 



In the course of these experiments many different poisons were 

 used and it was found that nearly all arsenicals were effective to a 

 certain degree but that the best results could be obtained with either 

 a di- hydrogen lead arsenate containing not less than 32 per cent, of 

 arsenic pentoxide, or a calcium arsenate containing at least 42 per 

 cent, of arsenic pentoxide ; both of these gave an effective control, 

 if properly used. It may also be possible to dilute these considerably 

 with some cheap carrier such as lime, though this has not been definitely 

 determined. The physical condition of the poison is fully as important 

 as its chemical composition, the finer powder being more readily 

 taken up by the dew and held in suspension for the weevils. Hence 

 the most eff'ective form of the above poisons has been powder of a 

 density ranging from 80 to 160 cubic inches per pound, 



(C538) c2 



