22 NATURAL CONTROL OF THE COTTON BOLL WEEVIL. 



field attacked. Frequently the plants leaf out and form squares 

 after having been defoliated. It must, therefore, be placed rather 

 low in the list of factors concerned in the natural control of the boll 

 weevil. 



It is possible that something can be done > to increase the efficiency 

 of this factor or to render it of more constant value, especially in such 

 regions as the Red River valley of Louisiana, where the worm occurs 

 with considerable regularity. It is evident, however, that the planter 

 should not rely upon the leaf worm to secure the destruction of his 

 stalks at as early a date as the picking of the crop may render possible. 

 At present in the bulk of the infested territory it may be considered 

 as an occasionally valuable factor, but the completeness of the con- 

 trol resulting from its occasional work is a most valuable demonstra- 

 tion of the effect which it is possible for the planter to secure quite 

 regularly by himself destroying the food supply of the boll weevil 

 early in the fall. 



The irregularity of the leaf-worm attack makes it necessary that 

 final conclusions as to its value in controlling the weevil be based 

 upon observations extending over a number of years, but the data 

 already collected show conclusively that with these two important 

 pests of cotton present in abundance the leaf-worm work is a most 

 positive benefit to the planter; and if it secures continuous defoliation 

 until too late in the season for the weevil to resume its breeding, this 

 may result in the practically complete control of the insect for the 

 following season. 



There can be no doubt that birds are an important factor in pre- 

 venting the extraordinary multiplication of many species of insects. 

 Considerable attention has been given to the determination of the 

 value of various birds as destroyers of weevils, and this important 

 work is being continued by the Biological Survey. These records 

 show that birds do not yet constitute a very important factor in 

 controlling the boll weevil. There are several reasons for tins. The 

 habits of the weevil are such that the adults are but slightly exposed 

 to the attack of birds, except during the season of the fall dispersion. 



In Cuba Mr. E. A. Schwarz has determined that a bird {Icterus 

 Jiypomelas) has learned to tear open the fallen squares and eat the 

 weevil stages infesting them, but in the United States no bird has 

 yet acquired such a habit. The season at which birds capture most 

 weevils is during the dispersion in the fall months, when the weevils 

 are flying most abundantly. The destruction of a large number of 

 weevils late in the season can not, however, be as effective in con- 

 trolling the weevil as would be the capture of a comparatively few 

 during the hibernation season or in early spring, but during the first 

 half of the season very few birds frequent the cotton fields. For 

 these reasons birds must be ranked low among the controlling factors, 



