156 



INSECTICIDES. 



From the very beginning of the laboratoiy work on the boll weevil 

 much attention has been given to testing the most promising insecti- 

 cides. As one result of the offer of a |50,000 prize by the State of 

 Texas for an efficient remedy for the boll weevil, a very large number 

 of supposed remedies have been proposed. Doubtless the inventors 

 have been perfectly sincere in their faith in the efficiency of these 

 compounds. As was fully anticipated by the entomologists when the 

 prize was offered, the commission charged with awarding the prize 

 has been deluged with applications therefor, the claims, in a large 

 majority of cases, being based upon some concoction supposed by the 

 inventor to possess marvelous insecticidal properties. In compara- 

 tively few cases had the new product been tested in any way. Often 

 samples were sent with the request that tests be made. Many of these 

 inventions found their way to the boll weevil laboratory at Victoria, 

 where it has been the uniform policy to give every such thing a fair 

 test and report the results to the originator. Tests were made in the 

 field upon weevils confined b}^ cages (PL XXI, fig. 86). This work has 

 required a great deal of time, and the results have failed to indicate a 

 single new compound having real value. Many of the substances 

 tried had absolutely no effect on either plant or insect life, while others 

 were equally fatal to both wherever they came in contact with them. 

 The primary difficulty with ail such insecticides lies in the fact that, 

 owing to the peculiar habits and life histor}^ of the weevil, the poison 

 can not be so applied as to reach the immature stages at all, and it can 

 not reach the adults so as to cause sufficient mortality to result in any 

 considerable benefit to the crop. 



The most promising and, as it has been found also, the most efficient 

 of all the insecticides tested v/as Paris green. Much work has been 

 done in thoroughly testing the effect of this poison. The most impor- 

 tant results of this work have already been published in Farmers' 

 Bulletin No. 211 of this Department, and need not be restated here. 

 The conclusion based upon these results is that the beneficial effect 

 resulting from applications of Paris green is rarely sufficient to repay 

 the expense of the treatment. It has been found that a small per- 

 centage of weevils can be killed, but under general field conditions the 

 benefit, if an}^, is too slight to justif}^ a recommendation for the use of 

 the poison. 



Among 40 other compounds tested, none proved worthy of even 

 passing consideration for field use. As a f umigant for seed, among the 

 eight gases or vapors tested (PI. XXI, figs. 87 and 88), carbon bisulphid 

 was found to possess considerable value when applied in the special 

 manner described under topic "Treatment of seed for shipment," 

 on p. 126. 



