102 



Almost all of the above named insects are sufficiently numerous at 

 times, when working alone, to kill or at least to greatly retard the 

 growth of the tree or trees upon which they feed. Of course, they do 

 not all occur at once in any given locality in such overwhelming num- 

 bers, nor are the injuries the same every year ; but quite frequently 

 two or more of the species are found feeding in company upon the same 

 tree in numbers sufficiently greatto do harm. In addition to the species 

 named above there are a great many others that are also known to at- 

 tack and injure the trees growing upon tree-claims ; but these latter 

 have not yet made their presence so strongly felt as to force us to place 

 them on the list of insect pests in connection with tree-claim culture. 

 For a description and life history of many of these the reader is referred 

 to Bulletin No. 7 of the United States Entomological Commission, en- 

 titled " Insects Injurious to Forest and Shade Trees." 



Causes for these Insect Injuries. — There is a cause for everything, so 

 in the present instance we must look for one or a combination of causes 

 that work together in producing the undue increase of insect life upon 

 the prairies when new varieties of plants are introduced. A very 

 superficial survey of the ground will quickly reveal to us some of these 

 causes. 



In the first place, there are always a few dwarfed trees of most of the 

 kinds that are usually planted upon claims. These trees are scattered 

 along the water courses, in ravines and gulches, andafew other localities 

 that are protected from the fires which have annually swept over the 

 broad prairies for generations. These few trees furnish food for small 

 colonies of the various species of insects that we have named. There 

 are always enough of them to very quickly stock a claim close by upon 

 which small trees are planted that are to their taste. Then, too, all of 

 these injurious insects are of a hardy nature, used to a precarious life, 

 and are strong fliers capable of making comparatively long journeys in 

 search of food for themselves and their progeny. They are, in fact, the 

 nomads of the insect world, capable of withstanding the vicissitudes 

 belonging to a life upon the vast prairies where the more delicate para- 

 sitic forms could not live or even find shelter. Then, too, their 

 requirements for quarters in which to pass the long, cold winter months 

 are less complex than are those of the species that come later on. 



In the second place, the country being destitute of groves of timber 

 among the branches of which insectivorous birds can find shelter and 

 build their nests most of these insect destroyers are absent. Of course, 

 the absence of so great a factor as are these birds in the ridding a 

 country of its insect pests soon becomes apparent in the increase of the 

 latter and of the accompanying injury done by them. The absence of 

 groves, too, not only keeps away the feathered tribe, but also prevents 

 many of the more delicate parasitic and a large number of the preda- 

 ceous insects from becoming established in the region. The majority 

 of these latter forms of insects, as before stated, are such as require 



