ECONOMIC PROBLEMS 85 



find efifective means of applying the results of eco- 

 logical discoveries in practical control. It is impor- 

 tant to distinguish clearly between economic ecological 

 problems and the solution of these by ecological 

 methods. The first stage in attempted control of 

 the situation should always be the collection of 

 adequate information about the whole ecology of 

 the animals studied. This is the staiff work. No 

 battle can be fought successfully without some 

 reasonably good information about the country and 

 the disposition of the enemy forces and his numbers 

 and the habits of his alHes. Thus the habitats of 

 dijfferent tsetse flies are accurately known, some- 

 thing of their numbers in different habitats, their 

 life history, enemies, parasites, and the animals they 

 feed upon to get blood. The second stage is to 

 invent practical methods of control. This may or 

 may not be possible through ecological methods. 

 Thus an insect pest may be controlled in one case 

 by parasites (as with the gypsy moth), in others by 

 ploughing (as with the corn-borer moth), in others 

 by spraj^ing with chemicals (as with many orchard 

 pests). The ecological information gathered by the 

 prehminary survey is necessary in order to direct 

 efforts on to the weak spot in the animal's life, but 

 this attack niay be made either by ecological or by 

 other means. The tsetse fly has so far proved 

 resistant to biological control, although success is 

 being achieved by removal of its optimum habitat 

 by burning the bush. 



What are the ways in which animal ecology can 

 take part in the solution of these problems, apart 

 from general surveys for information purposes ? 

 One way is to foUow the spread of introduced animals 

 and forecast (by climographs or other ecological 

 methods) the potential distribution. This has been 

 done by Cook (1924) for the pale western cutworm 

 in America ; by Nichols (1933) for pure-bred sheep 

 flocks (spreading under man's encouragement) in 



