1916 - Howard, L. O. Report of the entomologist for the year ended June 30, 1916. 

 U. S. D. A. Bur. Ent. Rpt. 24 p. Aug. 24. Wash. 



"Investigations of southern field-crop insects showed that the boll weevil 

 was the principal pest to be considered in relation to cotton culture. A new type 

 of poison dust gun and also a form of lead arsenate containing a higher percent- 

 age of arsenic were tested with excellent results in increased production." 



1918 - Coad, B. R. Recent experimental work onpoisoning cotton boll weevils. U. S. D. A. 

 B. 731, 15 p., 10 fig. July 19. Wash. 



Attempts to control the Mexican cotton boll weevil by the use of poisons have 

 been made almost from the time of its first appearance; the results, however, 

 have always been discouraging. This is attributed to the fact that the weevil de- 

 rives its food from deep punctures, thus ingesting very little of the poisoned ex- 

 ternal 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 drink. 



The first tests of this nature were begun in 1915. The results showed that 

 every poisoned plot yielded more than the untreated controls, the most pro- 

 nounced feature being the greater increase in yield with the larger number of 

 poisonings. Thus, with 4 applications, a gain of about 15% was secured; with 5, 

 this gain was increased to about 35%; while 6 applications increased it to 70%. As 

 all applications 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 

 applications late in the season seemed obvious. 



Similar experiments in 1916 were carried out, the results being quite as 

 definite as those of 1915, demonstrating the importance of applications late in the 

 season. 



About the middle of August 1917, experiments on a large scale were possible 

 where late planting and adverse weather conditions had combined to produce an 

 exceptionally heavy weevil infestation. One application of poison was given, and 

 10 days later the number of punctured squares had been reduced from 86% to 36%, 

 thus showing poisoning to be a very profitable operation. 



In the course of these experiments many different poisons were used, and 

 nearly all arsenicals were effective to a certain degree. The best results, how- 

 ever, could be obtained with either di-hydrogen lead arsenate, containing not less 

 than 32% of arsenic pentoxide, or with a calcium arsenate containing at least 42% 

 of arsenic pentoxide. Both of these were effective controls, if properly used. The 

 physical condition of the poison was fully as important as its chemical composi- 

 tion, the fine powder being more rapidly taken up by the dew and held in suspen- 

 sion for the weevils. The most effective forms were powders of a density ranging 

 from 80 to 160 cubic inches per pound. 



The optimum season of application was at the time when the weevils were 

 doing their maximum injury to the crop and when the cotton manifestly slackens 

 in blooming. Once a week constituted an effective interval between applications. 

 Much more effective poisoning with dry dust could be conducted while the dew 

 was on the plants. It was found advisable to poison as much as possible during 

 the evening, night, and early in the morning- -during the day only in case of 

 emergency. 



The experimental average of 5 lbs. per acre was obviously excessive; with 

 improved machinery, effective poisoning was accomplished with a much smaller 

 amount. The number of applications varied with the size of the plot to be dusted. 

 A single application over a large area was as effective as three on a small one 

 because of the constant migration of further weevils into the latter. 



The cost of treatment varied widely. In experimental work it averaged about 

 80£ an acre for each application. With improved machinery and the use of car- 

 riers this can be much reduced. A further economy may be effected if several 

 applications are given that part of a plantation near the hibernation quarters of 

 the pest before the weevils have become sufficiently abundant to start movement. 

 The remainder may then need only a single application. 



