PARASITE INTRODUCTIONS 395 



State is physiographically isolated to an exceptional degree. 

 Much of the country was originally desert, and has been brought 

 under cultivation through the development of irrigation, which 

 has established sub-tropical conditions in its southern territory. 

 The insect fauna in such parts is consequently largely introduced 

 and built up of immigrants from adjoining territory with certain 

 accidental importations from abroad. Compared with the rest 

 of the continent, the climate is wonderfully equable in the long 

 tract of country between the mountains and the sea. The area 

 where parasite introductions have been made covers the zone of 

 citrus cultivation in the south, which is exceptionally uniform 

 ecologically and circumscribed by physical conditions. 



Conditions apparently analogous to those found in California 

 occur in other parts of the world. As Tillyard has observed, 

 Australia is made up of a number of diverse areas separated from 

 each other by mountain barriers or great stretches of desert. 

 Looked at from this point of view. Western Australia, the elevated 

 apple lands of South Queensland and other parts, should offer 

 favourable conditions for the application of biological control. 

 Egypt, limited as it is by desert and sea, Mesopotamia, Palestine 

 and other lands would also appear to afford ideal conditions for 

 parasite introductions, provided judicious selection, based upon 

 sound preliminary investigation, be exercised (vide also Myers, 

 1928). 



(c) Wide Continental Areas. Biological control applied to 

 imported pests menacing crops widely distributed over vast 

 continental areas has to contend with manifold difficulties. 

 Competent investigators have expressed serious doubts whether 

 the method is likely ever to prove really efficient under conditions 

 of this character. The United States suffers more than any other 

 region of the world from the depredations of pests now disseminated 

 over immense tracts of territory. In the case of the gipsy and 

 brown-tail moths parasite introductions have been going on for 

 over a quarter of a century. More recently attention has also 

 been directed to the alfalfa weevil, the European corn-borer and 

 the Mexican bean beetle. The corn-borer, for example, now 

 infests well over 300,000 square miles of territory, while the areas 



