﻿VIU 



transported alive to the country where it is needed, and again 

 the discovery and successful transportation alike count for noth- 

 ing economically, unless it can be established at large after its 

 arrival. It is no doubt in many cases decidedly more easy to 

 discover natural enemies of an insect pest than it is to establish 

 them in a new and distant country. We have heard some, who 

 profess to be in favor of the repression (jf injurious insects l)y 

 means of natural enemies, talk of the discovery of a parasite, 

 as though the fact of this discovery were all important, whereas 



we must repeat that unless the parasite can be successfullv in- 

 troduced and established and duly performs its share of work in 

 controlling the pest, the discovery is of insignificant impor- 

 tance. Further, cases where a single natural enemy is alone 

 sufificient to keep down an injurious insect are rare and excep- 

 tional, and few pests are to be kept down in this way. As a rule, 

 it is a complex of causes that keeps an insect in check, often 

 the joint attack of various parasites and predators, and it may 

 be various diseases and other conditions combined. Only in 

 exceptional cases can the economic entomologist hope to suc- 

 ceed with a single parasite, as any practical field worker must 



