254 INSECTS 



control or affect insects with which the imported species 

 is not famiHar in its native home. Here we are not 

 making use of an adaptation, but are rather attempting 

 to create one. Such experiments may be crowned with 

 success, but it will be a success which cannot be pre- 

 dicted and it will depend on factors not apprehended 

 by the experimenter. 



While we have, undoubtedly, introduced into our 

 country numerous first class pests — the brown-tail and 

 gypsy moths among the latest — it is equally true that 

 dozens of species have been introduced on imported 

 stock or in other ways, that have never secured a foot- 

 hold; and we have a few species that have started out 

 as if to sweep all things before them and have gradually 

 died out so as to become almost extinct. Two such 

 species have been enemies to pear trees — the pear midge 

 and the sinuate pear borer; the latter of which never 

 got much beyond New Jersey, after destroying nearly 

 all the pear trees in one district. One species, the 

 "horn-fly," created enormous alarm among owners of 

 cattle for a few years, swept over a large part of the 

 United States and Canada in less than a dozen years, 

 and is now so rare where it first appeared that speci- 

 mens are at a premium for collectors. In none of these 

 cases are specific natural enemies to be credited with 

 the disappearance of the species. Conditions simply 

 were not suitable in all respects, and the insects failed 

 to adapt themselves Avith sufficient completeness to 

 survive in the long run. 



The important point is that those species that do 

 survive the introduction are exceptional in vitality and 

 adaptability, and are therefore naturally abundant and 

 able to maintain a lead over all their enemies. If the 

 specific parasite or other check of such a form does not 

 exist in the new country, and is not introduced with it, 



