96 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



these (1) the Permanent Region, which included the highlands of 

 Montana, Wyoming, and Colorado, formed the native breeding- 

 grounds, where the species was always found in greater or less 

 abundance;* (2) the Subpermanent Region, which included Man- 

 itoba, the Dakotas, and western Kansas, was frequently invaded; 

 here the species might perpetuate itself for several years, but 

 disappeared from it in time; (3) the Temporary Region, which 

 included the States bordering the Mississippi River on the west, 

 was that only periodically visited and from which the species 

 generally disappeared within a year. 



Spread When for various reasons the locusts became excess- 

 ively abundant in the Permanent Region they spread to the 

 Subpermanent Region, and from there migrated to the Tem- 

 porary feeding-grounds. It was the latter area which suffered 

 most severely from their attacks, but, fortunately, they did 

 not do serious injury the next year after a general migration. 

 In the Subpermanent Region their injuries were more frequent 

 than in the Temporary, but were hardly as severe or sudden as 

 farther east. Migrating from their native haunts, flights of 

 the grasshoppers usually reached southern Dakota in early sum- 

 mer, Colorado, Nebraska, Minnesota, Iowa, and western Kansas 

 during midsummer, and southeastern Kansas and Missouri 



FIG. 73. Rocky Mountain locust; adult and different stages of growth of 

 young. (After Riley.) 



during late summer, appearing at Dallas, Texas, in 1874, and about 

 the middle of October, and even later in 1876. As- thus indi- 

 cated, the flights were in a general south to southeasterly direction, 

 while west of the Rockies they descended to the more fertile 

 valleys and plains, but without any such regularity as eastward. 

 While the rate of these flights was variable and entirely dependent 

 upon local weather conditions, twenty miles per day was con- 

 * Bull. 25, U. S. Dept. Agr., Div. Entomology. C. V. Riley. 



