g Farmers' Bulletin 872. 



peas, and alfalfa. Thus in the Southern States most of the over- 

 wintering insects will be found in soil where cotton and other late- 

 growincr'^crops are raised, while in the North the late cornfields prob- 

 ably contain most of them. 



The bollworm shows a preference for corn when this crop is 

 " silking," and this fact can be utilized to some extent in protecting 



cotton and other crops 

 from injury, as will be 

 pointed out later. These 

 caterpillars are cannibalis- 

 tic, and when they come in 

 contact with one another 

 many of them are killed, 

 which usually reduces the 

 number of worms develop- 

 ing in a single year to 

 one, two, or at most three, 

 whereas dozens of eggs 

 may be laid upon a single 

 strand of corn silk. 



CONTROL MEASURES. 



As a result of the study 

 of the life history and the 

 seasonal history of this in- 

 sect it will be seen that 

 there are four outstanding 

 facts which can be made^ 

 use of in control work : 



First^ the insects spend 

 the winter in the pupa 

 stage in the ground. They 

 also spend some time be- 

 tween generations in the 

 soil. This enables the 

 farmer to destroy many of 

 them by plowing at the 

 proper time. 

 Second, the caterpillars feed for a time on the surface of the 



leaves before penetrating the tissues of the plant. This is the only 



time during which the insect can be poisoned successfully. 



Third, the number of bollworms or earworms increases greatly 



as the season advances. This indicates a need for hastening the 



maturity of all crops affected. 



I 



Fig. 6. — Vertical section through, soil, showing 

 pupa of bollworm in its burrow. About natural 

 size. (Redrawn from Quaintance and Brues.) 



