2 THE COTTON WOEM OK COTTON CATEEPILLAK. 



insects from the plants and preventing tlieir invasion of the fields 

 by means of ditches. Early in the seventies the whole situation was 

 revolutionized by the discovery that the worms could be poisoned 

 quickly and economically by the use of Paris green or other arsenical 

 compounds. The practice of controlling the insect by these means 

 soon became universal in the South. Planters everywhere obtained 

 large supphes of poison each season exactly as other regular plan- 

 tation supplies were procured. As soon as the defoliation began the 

 poisons were applied. This checked the outbreak on the plantation 

 at the beginning, whereas without the use of the arsenicals it would 

 have spread over the entire cotton acreage. About the same time 

 certain changes in agriculture in the South also contributed in a 

 very decided manner to the reduction of the importance of the pest. 

 The large cotton fields began to be broken up into smaller fields 

 planted to a variety of crops. This system of diversification of 

 itself prevented such great increase in the number of the worms as 

 had taken place in previous years. These two facts together seemed 

 to indicate for many years that the cotton worm was no longer to 

 be feared as an important enemy of the cotton plant in the United 

 States. 



For 21 years prior to 1911 the cotton worm had not been generally 

 abundant in the United States, although there was local damage 

 of some severity during different years in that period. Indeed the 

 passing of the insect had come to be considered such a settled fact 

 that the outbreak of 1911 was as surprising to the cotton planters 

 as to entomologists. 



THE OUTBREAK OF 1911. 



The outbreak of 1911 did not originate in the United States, but 

 in Central or South America. The moths flew northward very 

 early in the season and reached the neighborhood of Brownsville, 

 in Texas, by April. By the middle of June practically all of the 

 cotton fields in the vicinity of Brownsville that had not been pro- 

 tected by the use of poisons had become defohated. The new gene- 

 rations of the insects flew northward and eastward during June and 

 July. Duiing the latter month there appears also to have been 

 another invasion of the United States from South America. This 

 reinvasion took the moths into the South Atlantic States, where 

 they were soon found in very great numbers. They bred with great 

 rapidity and spread northward and westward. In August the west- 

 ern and eastern invasions coalesced, and witliin a few weeks the 

 insects were numerous in cotton fields tliroughout the belt. 



Later in the season many of the motlis wliich developed in the 

 cotton fields of the South flew northward, where they attracted con- 

 siderable attention. Mllions of individuals were found in Wash- 



