ECONOMIC PROBLEMS 81 



potatoes, corn and grain, and hundreds of other 

 crops on the one hand, and thousands of msurgent 

 insect pests on the other. \^ast sums of money are 

 lost through the destruction of crops, and very 

 considerable sums are spent in attempts to combat 

 the pests. To a certain extent such pest problems 

 are cumulative : insects are constantly being carried 

 round the world to new countries, in spite of stringent 

 importation regulations and quarantine inspectiott^ 

 The impact also comes in from the spread of the 

 cultivation of a particular kind of crop into regi6ns 

 where it was not known before. Apparently ^)\e 

 olive fl\- {Dacus ohac) used to occur on wild olivies 

 in North Africa, and then spread into the cultivatkl 

 olive plantations of southern Europe. On the other 

 hand, the development of sugar-cane production oh 

 a large scale in Trinidad gave opportunities for ai*i 

 indigenous froghopper [Tomaspis saccharina) to 

 become a pest by spreading the root fungi which 

 cause Froghopper Blight. An enormous volume of 

 economic biological research is produced annually, 

 and may be followed in the Review of Apinlied 

 Entomology, issued by the Imperial Institute of 

 Entomology. The application of ecological ideas to 

 these problems is as yet negligible, except perhaps 

 in the realm of biological control and in the applica- 

 tion of climograph methods. 



Stored products in warehouses and factories and 

 shops are also attacked by a great numljer of pests 

 (Richards and Herford, 1930). Here the problem of 

 control is different, owing to the possibihties of 

 regulating the physical environment. 



Forestry problems are always complicated much 

 by the fear of periodic pest damage. Eidemann 

 (1931) has shown that the incidence of defoliating 

 tree-pests in the German forests during the last 

 hundred years tended to fall into cycles of damage 

 and freedom from damage. The working out of 

 forestry operations on paper — and the profits form 



