SB 

 818 

 C578 

 ENT 



NO. 33, Second Series. (Supplementary to Circulars is and 27.) 



United States Department of Agriculture, 



DIVISION OF ENTOMOLOGY. 



REMEDIAL ^VOKK AGAINST THE MEXICAN COTTON-BOLL WEEVIL. 



In the course of the investigations of the holl-vveevil problem in 

 southern Texas in the spring of 1896 by 1113' first assistant, Mr. 

 C. L. Marlatt, it was earlj' discovered that the overwintered weevils 

 were not onlj^ collecting on the volunteer cotton but were feeding to 

 a noticeable extent on the expanding leaves and soft green stems of 

 the new shoots. The possibilit}^ of destro3'ing the beetles bj^ wetting 

 this new growth b}' an arsenical poison at once suggested itself, and 

 experiments which were promptly instituted with confined beetles on 

 small plants demonstrated conclusively that not only do the beetles 

 feed on the leaves and tender shoots voraciously, but that by poisoning 

 such shoots the beetles subjected to experiments could all be killed 

 in the course of eight to twelve hours. 



A more general experiment to test the value of poisoning was 

 instituted in a field containing much volunteer cotton which had 

 already (April 26) made considerable growth, forming rather dense 

 bushes. This experiment was carried out on the farm of Judge 

 Borden, of Sharpsburg, the plants being sprayed from an ordinary' 

 wagon cart. Great difficulty was experienced in wetting more than 

 the outer leaves, which were now of large size and protected much 

 of the inner growth, especially the squares. The outcome of this 

 work demonstrated that while the poisoning of the cotton plant was 

 thoroughly feasible and practicable when done at the right season 

 and would result in the killing of the overwintered weevils, if delayed 

 too long it was very unsatisfactory and promised very little of value. 

 In other words, it is much more difficult to poison plants successfully 

 as a means of destroying the weevil than to poison them for the 

 cotton-leaf worm, which feeds very often if not generally on the outer 

 leaves and can be reached by powder dusted over the plant in the 

 most careless and general way. The weevil, on the other hand, feed- 

 ing as it does on the tender growing tips and on the flower buds, 

 which are very often concealed and covered up by the larger leaves 

 of older growth, requires for its destruction very careful and thorough 

 spraying, such as would be impossible after either volunteer or planted 

 cotton has reached any considerable size. 



