NATURAL CONTROL. 135 



cent. Bolls on fertilized plats showed proliferation in 66.2 per cent of 

 the infested locks; on unfertilized plats in 69.5 per cent. 



It was found that proliferation very frequently follows the attacks 

 of any of the insects which injure the cotton boll or square. In the 

 case of these other insects the phenomenon is of little importance, 

 since, unlike the weevil, they generally make punctures merely for 

 the purpose of feeding. The immature stages are not developed in 

 the cotton fruit and are consequently beyond the reach of the growth 

 which the adults have incited. 



OTHER PHASES OF PLANT CONTROL. 



There are other forms of plant control which require attention. 

 Dr. O. F. Cook, of the Bureau of Plant Industry, has been the prin- 

 cipal student of this matter and has called attention to numerous 

 weevil-resisting adaptations of the cotton plant, although important 

 contributions have been made by several other investigators. Among 

 the more important properties or tendencies of the cotton plant which 

 affect the weevil adversely are: (1) Early bearing, (2) determinate 

 growth, (3) hairy stalks and stems (PL XIV, a), (4) abundance of 

 secretion from nectaries, (5) pendent bolls, (6) involucral bracts 

 grown together at base, (7) thick-walled bolls, and (8) tendency to 

 retain infested fruit (PI. XV). 



Early bearing enables the plant to produce its fruit before the 

 weevils have become numerous. In other words, it allows the plant 

 to take advantage of the small number of weevils which succeed in 

 passing the winter and also to take advantage of the comparatively 

 slow development of the insect during the early portion of the growing 

 season. 



Determinate growth prevents the maturity of numerous weevils in 

 the fall. Plants with this character well marked discontinue both 

 growth and fruiting. As the capacity of the weevil to increase is 

 limited very largely by the amount of fruit available, it is evident 

 that a variety which discontinues fruiting at an early date in the fall 

 must reduce greatly the number of weevils that are present to go into 

 winter quarters. 



It has been found that the presence of a considerable growth of hair 

 on the stalks and stems presents an important obstacle to the progress 

 of the weevil and consequently reduces the daily capacity of damage 

 of each insect. In some of the American upland varieties, notably 

 the King, this hairiness is developed to such an extent as to be a 

 form of protection of considerable importance. 



^As has been pointed out in another section of this bulletin, boll- 

 weevil parasites in the adult stage feed upon the nectar winch is 

 secreted by the cotton plant. Consequently the greater the secretion' 

 of nectar the more favorable will be the conditions for these important 

 enemies of the weevil. 



There is a more or less constant tendency on the part of the adult 

 weevil to frequent the upper portion of the cotton plant. If it hap- 

 pens to alight upon a lateral branch which has bolls or squares stand- 

 ing upright, attack follows immediately. On the other hand, if the 

 branch upon which the weevil alights has bolls which turn downward, 

 there is a considerable likelihood that it will work upward to other 

 lateral branches and overlook the fruit upon the first branch. 



