10 farmers' bulletin 799. 



its killing power. The more quickly the full killing strength of gas 

 can be attained, the more economical and effective the treatment is 

 likely to be. This method is used especially with cotton seed for 

 boll-weevil destruction. 



/ HOW CARBON DISULPHID KILLS. 



The way in which carbon disulphid kills has been studied at the 

 Michigan experiment station,* where the conclusions have been 

 reached that carbon-disulphid vapor very probably acts upon the 

 fatty tissues in the insect body, dissolving them to some extent ; that 

 it tends to coagulate the proteins; and that it prevents the assimila- 

 tion of ox3^gen and the carrying on of other processes which are of 

 ^dtal importance to insect life. A certain amount of respiration goes 

 on at all times so long as an insect is alive, but it is evident that res- 

 piration will be far less in the egg stage or during the dormant 

 periods in an insect's life than it is in the adult stage and during the 

 periods of its greatest activity. Tlie strength of vapor and the time 

 required to kill, therefore, will vary greatly and accordingly. Simi- 

 larly, slow-moving insects usually are harder to kill than the quick- 

 moving forms. 



TREATMENT FOR INSECTS INFESTING STORED GRAINS, PEAS, ETC. 



The most important use for carbon disulphid as an insecticide in 

 the United States is in the fumigation of stored grains, cowpeas, 

 beans, and peas to kill the insects infesting them. Many species of 

 insects are concerned in this inquiry, but all are susceptible to the 

 same treatment. The most important species attacking corn is the 

 so-called black weevil, or rice weevil,^ which causes a loss amounting 

 to several million dollars annually in each of the South Atlantic and 

 Gulf States. Probably half of this loss could be prevented by cer- 

 tain inexpensive changes in the methods followed in the planting and 

 handling of the corn crop, but for the other half no method of pre- 

 vention yet tested can equal fumigation with carbon disulphid. 



Investigation by the Alabama Experiment Station has shown that 

 the amount of liquid disulphid required for killing grain insects 

 under ordinary conditions of storage is much greater than has been 

 recommended usuall}'', and ranges up to about 20 pounds per 1,000 

 cubic feet in ordinary rooms where the walls and floor have not been 

 made especially tight, as recommended on pages 12-13. 



> Shafer, Oeorgt' D. How contact insecticides kill. In Mich. Agr. Col. Exp. Sta. Tech. 

 Bill. 21, p. 18, 1915. 

 - Oalandra oryza L. 



