8 FARMERS BULLETIN 872. 



out August undoubtedly is conducive to severe injury. This is par- 

 tially explained by the moistening of the soil, which permits the 

 moths to emerge without difficulty, and by the stimulating effect 

 of the moisture on the growth of stalks and leaves of cotton at this 

 time, which favors bollworm development. Furthermore, it has been 

 found that the prevalence of such weather conditions lessens the 

 effectiveness of certain minute parasites which prej^ upon the boll- 

 worm in the egg and larva stages. 



SEASONAL HISTORY AND RELATION OF ABUNDANCE TO CROP 

 GROWTH. 



As has been stated, the bollworm or corn earworm pupa passes 

 the winter months in the soil. Early in the spring the moths begin 

 to come out, and by the time corn is " knee high " they are ready 

 to deposit eggs. On account of the number of pupse which die from 

 adverse conditions in the winter, the first brood usually is small and 

 the damage is not so appreciable. The second brood appears about 

 the time the corn is in silk and tassel, and the number of moths is 

 increased greatly. The caterpillars reach their full development 

 about the time the ears of early corn become hard. In the South the 

 third generation is the one which is destructive to cotton, the corn 

 at this time being for the most part hard and dry. In the North 

 this brood develops on late corn and other crops, and under usual 

 weather conditions is the last brood of the season, while in the South 

 four or even five broods may develop during a year. The late 

 caterpillars feed on various green crops, including late cotton, cow- 

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

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

 growing crops are raised, while in the Xorth 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 cannibalistic, and when they come in contact 

 with one another many of them are killed, which usually reduces the 

 number of worms developing in a single ear 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 insect 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 between generations in the soil. This 



