THE BOLL- WEEVIL PROBLEM. 15 



Some of the important means of control to be described later are 

 based upon this consideration. 



Insect 'parasites. — The second of the important agencies provided 

 by nature for the control of the weevil is a large number of insect 

 enemies. These consist of a variety of forms which prey upon the 

 boU weevil. Forty-five species of these enemies are known. Of 

 these, 23 are parasites, which by means of their special organs place 

 eggs on the immature stages of the weevil within the square or boll. 

 The young of the parasite develop by feeding upon the boll weevils, 

 which they ultimately kill. Thus parasites instead of boll weevils 

 emerge from the injured fruit. The parasites seem naturally to be 

 increasing in numbers and effectiveness against the boll weevil. In 

 one instance in 1907 the mortality due to parasites in a field near 

 Robson, La., was 77 per cent. About the same time 61 per cent of 

 the weevils in a certain field near Victoria, Tex., were killed by para- 

 sites. These enemies of the weevil have existed in this country for 

 an indefinite time. Their natural habit has been to prey upon weevils 

 more or less related to the boU weevil that have occurred in this 

 country for many years. They never feed on vegetation. It is 

 undoubtedly true that they are now turning their attention from the 

 original hosts, which are generally not very numerous, to the boll 

 weevil, which offers abundant and favorable opportunities for repro- 

 duction. Thus they aUy themselves with the planter for the protec- 

 tion of the cotton crop. 



Other insect enemies. — In addition to the true parasites just de- 

 scribed, the boll weevil suffers from a number of insects which are not 

 parasites in a strict sense but prey upon it as food. The principal 

 ones of these predatory enemies are ants. Of these, 12 species are 

 known to attack the weevil. They are the minute brown ants and the 

 yellowish ants that occur frequently in cotton fields and are observed 

 running over the plants or on the ground. Their v/ork is not against 

 the adult weevils, but against the immature stages in the squares. 

 Some species devote their attention principally to the squares that 

 have fallen to the ground, while others habitually seek the insects 

 within the squares that remain hanging on the plants. The larva of 

 the weevil, incased in a tlnn covering, offers a source of food that the 

 ants are not inclined to overlook. They gnaw through the thin shell 

 inclosing the weevil larva, and the latter is soon destroyed. In some 

 cases more than half of the immature stages in fields have been found 

 to be destroyed by ants alone. To find 25 per cent so destroyed is not 

 a rare occurrence. 



Other factors in natural control. — In addition to the principal factors 

 in natural control which have l)een mentioned there are several of 

 minor importance. Among these may be mentioned that de- 

 velopment of plant tissue known as proliferation, which some- 



