12 THE UNIVERSITY SCIENCE BULLETIN. 



molted skins, some of which, at least, will usually be found 

 clinging to the leaf or grass blade. 



The injury to plants by the Cicadettidse may be divided into 

 two groups. First, the sucking of the plant juices till the 

 plant is killed or its vitality so reduced as to result in a re- 

 duced yield of food or fruit. Second, the transmission of 

 plant diseases. Much work has been done on the former 

 group by Professor Osborn, and on the latter by Doctor Ball. 

 In the following discussion I have drawn very largely from 

 the work done by them. 



The matter of the reduction of the yield due to the sucking 

 of the plant juices, is rather a peculiar one. Or perhaps it 

 reveals a rather peculiar turn of mind in mankind. I believe 

 it shows that there is still a great field of development for 

 economic entomology and a field which should receive much 

 attention. 



In the main, agriculturists and many entomologists have 

 turned their attention to fighting those insect pests which do 

 very visible and usually a very serious amount of damage. 

 The average farmer will at once notice a pest that will destroy, 

 in a mass, several rows of his corn. Or he would notice at 

 once, and fight with all his energy, anything that picked out 

 about every tenth hill and utterly destroyed it, though not 

 touching the other nine hills. But the same man seemingly 

 pays no attention to any pest that reduces in the aggregate 

 the yield of the whole field to the amount that would have 

 been produced by the destroyed rows or by the every tenth 

 hill, as long as he sees no very apparent and severe damage 

 and the field as a whole seems to be doing fairly well. The 

 same would apply to wheat and oats, rye and barley, alfalfa 

 and clover, prairie hay and pasture. The question ought to be, 

 not how much did the field raise, but what could such a field 

 yield if no damage whatever be done by injurious insects? 



No matter what the crop, or what any one's views may be 

 as to the damage done by leaf hoppers, all must agree that 

 every little bug takes some of the life juices that belong to 

 the plant, and that this multiplied by hundreds or thousands 

 cannot but help reduce the yield of the crop infested. So it 

 is with this thought in mind, namely, that we ought to strive 

 after the best possible yields, yields not hampered nor re- 

 duced by insect pests, that we turn to discuss the damage 

 done by leaf hoppers to the various crops. 



