94 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



many years. This was brought about by a series of dry years, 

 which have resulted in the abandonment of farms in many places. 

 It is, of course, well understood that the absence of serious damage 

 since 1876 has been partially due to the settling up of valleys in 

 the permanent region. I wish to make it clear, however, that the 

 dryness is the primary and the abandoning a secondary cause." 

 " Serious injury has occasionally been done in restricted 

 localities in Minnesota, the Dakotas, Montana, and Manitoba, 

 but in recent years it has been difficult to find the species except 

 in the mountains, and it will probably never again be a plague in 

 the Central States." 



The Rocky Mountain Locust 



Let us first consider the species which has been the most 

 injurious, as the other locusts differ from it in but few essential 

 points other than in being non-migratory. 



To correctly understand its habits the reader should first 

 divide the area which this species affected into three parts. Of 

 these the (1) 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 

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



