Insect Pests of Interkst to Cotton Growers 181 



THE cotton leaf worm 



The cotton leaf worm, (Alabama argillacca llubu) is one of the 

 best known cotton insects of North America. It is not known to 

 have any other food plant than cotton, including the Arizona wild 

 cotton. This insect is believed not to winter over as rule in the 

 United States but to come in each season by flight of the adults from 

 Central and South America. The moth is of an olive gray color, 

 with a wing expanse of one and one-third inches. Eggs are laid 

 singly on the under surfaces of the leaves near the top of the plant. 

 Each female lays about 500 eggs. These hatch in three or four 

 days and the larvae at first are of a pale yellow color but soon 

 become greenish. The full grown worms are nearly half an inch 

 long, slender, bluish green in color with black spots and frequently 

 with black stripes along the back. They walk by looping and 

 when disturbed drop from the plant. \Vhen full grown the worms 

 spin light silken cocoons on the cotton plant, usually within a fold 

 of the leaf, and transform to brown pupae. The moth develops 

 from the pupa in the course of a week in warm weather. Several 

 generations occur during a season, and the insects multiply at an 

 almost unbelievable rate. It has been estimated that if it were 

 not for the destruction of many of the insects by natural enemies 

 the progeny of one female moth in four generations would amount 

 to more than 300,000,000,000 individuals. The third generation, if 

 placed end to end, it is said, would encircle the earth more than 

 four times at the equator. 



Fortunately there are a great many natural enemies of the cot- 

 ton leaf worm which help to prevent excessive multiplication. In 

 past years before the boll weevil entered this country, the cotton 

 worm was regarded as a pest and poisoning of the cotton plants for 

 its destruction was commonly practiced. Since the boll weevil 

 made its appearance, however, the work of the cotton worm has 

 not been regarded as serious as a rule, and in a great many cases 

 it has been recognized as a distinct advantage, owing to the fact 

 that the partial defoliation has tended to hasten maturity of the 

 bolls, and the stripping of the plants has deprived the late emerging 

 boll weevils of a much needed food supply. 



In Arizona the cotton leaf worm has been found attacking cot- 

 ton in the Salt River Valley, the Gila Valley, and near Tucson. It 

 has also been found attacking the wild cotton plant, which has 

 already been mentioned as a food plant of a variety of the cotton 

 boll weevil. The cotton leaf worm does not appear every year in 



