8 

 LIFE CYCLE. 



There are four distinct stages in the life cycle of the boll worm, as 

 is the case with all butterflies and moths — namely, the egg, larva, 

 l^upa, and adult. 



The egg. — The eggs of the boUworm moths are deposited upon 

 various plants and other objects, mainly, however, on the favorite 

 food plants of the larvae — corn, cotton, and less frequently on toma- 

 toes and tobacco. They are quite small (about one-fiftieth of an inch 

 in diameter), whitish objects, and may usually be seen in numbers 

 on fresh corn silks or scattered about on the leaves of corn or upon 

 the foliage and fruit of cotton, though in the latter instances they 

 are less easily seen, owing to their pale color. The accompanying 

 figure (fig. 1) shows the peculiar sculpturing of the egg surface as 

 seen with the aid of a magnifier. 



The number of eggs laid by a single moth varies from about 300 to 

 nearly 3,000, with an average of about 1,100. 



The temperature has a decided influence upon the length of the egg 



stage. It varies from two and one-half 



days during the summer months to eight 



days or even longer in the spring and fall. 



The larva. — The larva is the destructive 



^ , ^ , ^ ,, . , , stage of the insect and, of course, the one 



Fig. 1.— Egg of bollworm; side ana » ^ " ' 



topviews. mghiymagnifled(from uiost generally noticed. When first hatched 

 QuaintanceandBrues). -^ -g ^^^.^ ^^^^ ^^^ ^g usually Overlooked 



until its injury to the plant upon which the egg was placed becomes 

 severe enough to attract attention. This early period in the growth of 

 the larva is practically the only time when it may be destroyed by the 

 use of poisons. The period of growth of the larva is largely depend- 

 ent upon temperature and the abundance of the food supply. The 

 average length of this stage, in the summer months, is about sixteen 

 days. During this short period the larva grows from a tiny object 

 three-fiftieths of an inch in length to a stout worm 1| to 1^ inches 

 long. There is a decided variation in the color aiid markings of dif- 

 ferent individuals, nearly every gradation occurring from a pale 

 oreen throuoh rose color and brown to almost black. 



The pupa. — When the larva has completed its growth it leaves its 

 food plant, usually attempting to reach the ground by crawling; 

 it then selects a suitable spot, usually within 2 feet of the base of 

 the plant from which it crawled or fell, and burrows from 2 to 5 

 inches into the soil. A cell is then constructed running back to 

 within from one- fourth to one-half an inch of the soil surface. This 

 provision is made so that the moth may easily push off the cap of 

 the cell and escape. Wlien this cell is complete the larva molts its 



290 



