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 
most ly 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, 
