162 THE MEXICAN COTTON-BOLL WEEVIL. 



fumigated at frequent intervals by means of carbon bisulphid or col- 

 lected in a closed chamber and burned before the weevils have an 

 opportunity to escape. (See PI. X, a.) 



9. Fumigation of seed (fig. 34). This is a means of repression that 

 will be of avail only in the case of shipments of seed into uninfested 

 territory. It has been found that carbon bisulphid is the most sat- 

 isfactory agent to use. Great care should be taken to insure thor- 

 oughness of application. 



The use of a crossbar attached to the cultivator to jar the infested 

 squares from the plants has frequently been recommended. Under 

 some conditions this practice should be followed, but under others it 

 is worse than futile. It was shown, in the treatment of the subject 

 of natural control of the weevil, that in the humid region, including 

 Arkansas, Louisiana, and the eastern portion of Texas, the mortality 

 in hanging squares is greater than in fallen squares. For this reason 

 it is better for the squares to remain on the plants. There is another 

 reason why they should be allowed to remain on the plants which 

 applies especially to the moist region in which the boll weevil is now 

 doing great damage. This is, that the hanging squares are much 

 preferred by the boll- weevil parasites. The records have invariably 

 shown a higher rate of parasitism in hanging squares than in fallen 

 squares. In this way the hanging squares furnish a means for the 

 breeding of parasites, thereby enabling them to establish themselves 

 in the field. 



It will be noted that the means of repression of the boll weevil may 

 be divided into two classes, namely, direct and indirect. 



The direct means of control are the destruction of the weevils in 

 the fall by destroying the plants and burning or burying the immature 

 stages, hand picking of weevils and squares under some conditions, 

 the burial of the infested forms at the time of maximum infestation, 

 and the burning of the hibernating weevils in their winter quarters. 



The indirect means of control are early planting, the use of early 

 varieties and of fertilizers that will accelerate growth, the selection 

 of fields where the soil is suitable to rapid development, frequent 

 shallow cultivation, the encouragement of the parasites of the weevil 

 by placing the infested squares that may be picked by hand in cages 

 instead of burning them, and the use of machinery which facilitates 

 the various operations in preparing the land and cultivating the crop. 

 These have the effect of increasing the acreage that a hand may cul- 

 tivate. In view of the fact that the boll weevil forces a reduction in 

 the acreage per hand, this is a consideration of some moment. 



DESTROYING THE BOLL WEEVIL IN COTTON SEED. 



It has been shown in this bulletin that adult weevils are frequently 

 to be found in cotton seed and that there is danger in the dissemina- 

 tion of the pest through the shipment of the seed. A number of 

 experiments have been performed to discover means of killing the 

 weevils found in seed. There are great difficulties to be overcome 

 on account of the density of the seed and its practical impenetra- 

 bility by certain fumigants. It was shown, for instance, that hydro- 

 cyanic-acid gas has practically no penetrating power whatever. 

 Carbon bisulphid was found to be satisfactory, although a special 

 apparatus and special manipulation of the seed are necessary to insure 



