INSECTS INJURIOUS TO THE GRAINS AND GRASSES. 59 



To correctly understand its habits the reader should 

 first divide the area which this species affects into three 

 parts. Of these the (1) '' Permanent Eegion, including 

 the highlands of Montana, Wyoming, and Colorado, forms 

 the native breeding-grounds, where the species is always 



Fig. 32. — Rocky Mountain Locust. 



found in greater or less abundance.'^ * (2) The Sub- 

 permanent Region, including Manitoba, the Dakotas, and 

 western Kansas, is frequently invaded. Here the species 

 may perpetuate itself for several 3^ears, but disappears 

 from it in time. (3) The Temporary Region, including 

 the States bordering the Mississippi River on the west, is 

 that only periodically visited and from which the species 

 generally disappears within a year. 



Spread. — When for various reasons the locusts become 

 excessively abundant in the Permanent Region they spread 

 to the Subpermanent Region, and from there migrate to 

 the Temporary feeding-grounds. It is the latter area 

 which suffers most severely from their attacks, but, for- 

 tunately, they generally do not do serious injury the next 

 year after a general migration. In the Subpermanent 

 Region their injuries are more frequent than in the Tem- 

 porary, but hardly as severe or sudden as farther east. 

 Immigrating from their native haunts, flights of the grass- 

 hoppers usually reach southern Dakota in early summer, 

 Colorado, Nebraska, Minnesota, Iov\'a, and western Kansas 



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



