INSECTS INJURIOUS TO COTTON 245 



The larvae become full grown in from one to three weeks, during 

 which time they moult some five times. 



When mature the caterpillar crawls into a folded leaf, which is 

 often so eaten away that the pupa hangs exposed, and there 

 spins around it a thin silken cocoon and transforms to the pupa, 

 in which state the insect remains dormant for from one to four 

 weeks, when it emerges as an adult moth. 



The moth is a dull olive-gray color with a wing expanse of 

 about 1^ inches, which sometimes have a purplish lustre, and which 

 are marked with darker lines as shown in Fig. 173. Like most of 

 the owlet moths it flies only after sunset, but unlike them, it is 

 not confined to the nectar of flowers for food, as its mouth is 

 peculiarly adapted to piercing the skin of ripe fruit and feeding 

 upon its juices. The moths are strong fliers, those of the later 

 broods being frequently found as far north as Canada. 



The first two generations develop rapidly and in the extreme 

 South the moths emerge by early April and are carried north- 

 ward by the prevailing winds. Eggs deposited by them give 

 rise to a brood of moths which in turn fly further northward, 

 and thus the worms are gradually found throughout the whole 

 cotton belt, though with a considerable confusion between 

 the various generations. At least seven generations occur 

 on the Gulf Coast, and three at the northern limit of the 

 species. Considering the number of eggs laid by each female 

 and this number of generations, it may be readily perceived how 

 such immense numbers of the caterpillars may arise by the latter 

 part of the season, in a region where practically none remain 

 over winter. If none was killed, the progeny of a single moth 

 after four generations would amount to over 300,000,000,000 

 individuals, or if placed end to end, the third generation would 

 be enough to encircle the earth at the equator over four times. 



Enemies. It is thus very fortunate that there are many 

 deadly enemies of the cotton worms, which commence their war- 

 fare upon them with their first appearance in spring and continue 

 it with increasing ardor throughout the season. One of the most 

 effective of these is a minute little insect, Trichogramma pretiosa, 



