94 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 



ESTABLISHMENT AND DISPERSION OF THE NEWLY INTRODUCED 



PARASITES. 



In the beginning we were very far from accrediting to that phase 

 of the project which has to do with the establishment and dispersion 

 of the newly introduced parasites the importance which it deserved. 

 Many widely diverse species of insects were known to have been 

 introduced from the Old World and firmly established in America. 

 Presumably they were accidentally imported, as was the case with 

 the gipsy moth and the brown-tail moth; presumably, also, they had 

 spread and increased from a small beginning, at first very gradually 

 and later more rapidly, until they had become component parts of the 

 American fauna over a wide territory. The circumstances under 

 which the gipsy moth was imported were well known, and a good 

 guess had been made as to those which resulted in the introduction 

 of the brown-tail moth. But these were and are rare exceptions in 

 this respect, and for the most part the preliminary chapters in the 

 story of each of the insect immigrants never have been and probably 

 never will be written. 



Because the two very conspicuous instances of the gipsy moth and 

 the brown-tail moth were constantly and automatically recurring 

 whenever the probable future of the intentionally introduced para- 

 sites was considered, it was, perhaps, taken a little too much for 

 granted, that they were to be considered as typical and significant 

 of what to expect. In each instance the invasion started from a 

 small beginning, and while the subsequent histories were different, 

 the more rapid spread of the brown-tail moth was directly due to the 

 fact that the females were capable of flight, and the relatively slow 

 advance of the gipsy moth into new territory to the reverse. Even 

 the brown-tail moth was for some years confined to a comparatively 

 limited area, and it was rather expected that the parasites, if they 

 established themselves at all, would remain for a similar period in the 

 immediate vicinity of the localities where they were first given their 

 freedom. 



Accordingly, in accepting this theory without submitting it to a 

 test, attempts were made to encompass the rapid dissemination of the 

 parasites coincidently with their introduction. In 1906 and 1907 

 the parasites which were reared from the imported material were 

 mostly liberated in small and scattered colonies. In a few instances 

 this procedure was the best which could have been adopted ; in others 

 the worst. Small colonies of Calosoma, for example, remained for 

 several years in the immediate vicinity of the point where the parent 

 beetles were first liberated before any material dispersion was appar- 

 ent (see PI. XXIV), and the small colony was thus justified. 

 The gipsy-moth egg parasite Anastatus, as was later determined, 



