METCALF: HOMOPTERA AUCHENORHYNCHA 53] 



accurate measurements of all of the known factors in the different environ- 

 ments should command the study of future students. 



That the field of ecology has been too much neglected is abundantly evi- 

 denced. I need point out only a single example. Our studies of the great grassy 

 plains of the Missouri and Mississippi valleys have largely neglected the leaf- 

 hoppers and planthoppers which occur in a normal grasslands area. Yet Os- 

 born's studies showed many years ago that the total population of these insects 

 is of the order of one to two million individuals per acre. Now such an impor- 

 tant observation as that cannot be neglected in studying the sum total of all 

 of the factors, physical and biological, in the environment. 



There is great need for more careful studies in ecology from all parts of 

 the world. The inference of such studies on the development of the science of 

 ecology and of the economic control of insect pests is incalculable. Careful 

 studies such as are now being made by two Finnish homopterists, Lindberg and 

 Nuorteva, should be initiated by students in all parts of the world. 



Until about fifty years ago very little attention was given to the economic 

 importance of the Homoptera. However, a few species received some notice; 

 chief attention was given to the spectacular appearance of the seventeen- 

 year and the thirteen-year cicadas and little attention to the conspicuous but 

 relatively inconsequential damage done by the so-called buffalo treehopper. But 

 starting about fifty years ago a sequence of events impressed upon entomologists 

 the importance of the Homoptera in relation to crop damage. One of the earliest 

 and most spectacular of these incidents was the great destruction wrought to the 

 sugarcane fields of Hawaii by the sugarcane planthopper imported from Aus- 

 tralia or New Guinea and its control by introduced parasites. Also relatively 

 early was the damage caused by the sugarcane froghopper in Trinidad. Fol- 

 lowing this was the destruction by the potato leafhopper of potatoes, beans, and 

 peanuts, and the damage caused by the sugarbeet leafhopper to the growing 

 of sugarbeets in the western United States. More recently, the damage caused 

 by the alfalfa froghopper has again emphasized the importance of these insects 

 as pests of agricultural crops. 



Concurrently with the foregoing, or nearly so, there developed the apprecia- 

 tion of the economic importance of these insects, particularly the apple leaf- 

 hopper complex; various species of cotton leaf hoppers in Africa, India, and 

 Australia; the importance of the grape leafhopper in the United States; of leaf- 

 hoppers on cranberries in New Jersey; and of leaf hoppers and planthoppers on 

 rice, particularly in Japan. Other economic pests perhaps should be mentioned, 

 but most of these are pests of minor crops or are of only local consideration at 

 present. 



Another development is the importance of these insects as vectors of certain 

 diseases of crop plants. Recent important summaries of these have been pub- 

 lished, and mention should be made of such important diseases as curly-top of 

 sugarbeets and other types of curly-top transmitted by CircuUfer tenellus, of 

 peach yellows by Macropsis trimaculata, of the phloem necrosis of the elm by 

 Scaphoideus, and of various mosaic diseases and several kinds of yellows trans- 

 mitted by leafhoppers. 



The life histories of many of the economic pests belonging especially to the 

 leafhopper group have been studied but there are many other forms which 



