14 
PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 
England as nearly as possible the entire natural environment of the 
gipsy moth and the brown-tail 'moth in their native homes, similar 
conditions of comparative scarcity could surely be reached, and this 
view he still holds with enthusiasm. Naturally, in the course of the 
work as it progressed year after year his ideas have been changed as 
to methods, and very great improvements have been made upon the 
earlier methods, largely through the intelligence and ingenuity of 
the junior author of this bulletin. Moreover, the careful, intensive 
studies which have been made at the gipsy-moth parasite laboratory 
by the junior author and a corps of trained assistants, aided by 
abundant material, funds, and supplies, have resulted not only in the 
ascertainment of very many facts new to science, but in the accumu- 
lation of such facts to such a degree as to enable generalizations of a 
novel character and of a sounder basis than could have been had 
under other conditions. Many points are brought out in this bulletin 
which will doubtless be entirely new to the trained scientific reader. 
Mistakes have been made and wrong conclusions have been drawn 
from time to time, but these have been corrected, and we are now in 
a fair way to see a favorable result from the long and expensive work. 
The initial idea was that since a large percentage of gipsy-moth 
caterpillars or brown-tail moth caterpillars in Europe contains para- 
sites each year, therefore if these caterpillars were brought to America 
in large numbers from every possible place we could not fail to rear 
from them an abundance of adult foreign parasites. This idea was 
sound, and in following it out we have constantly improved the 
methods — methods of collection, of packing, of shipment, and of 
subsequent rearing. Very large numbers of parasites have been 
reared. 
It was first thought that when parasites had been reared in suffi- 
cient numbers they should be widely distributed in small colonies, on 
the theory that each colony would remain in substantially the same 
general locality and would increase and spread from that point. This 
idea was a natural one and was fully justified by previous work which 
had been done with parasites of other groups of insects, but in this 
case it proved to be erroneous, and valuable time and valuable speci- 
mens were lost. Eventually it was shown to be of prime importance, 
first to establish a given species of parasite in this country, and not 
until this lias been accomplished to pay any attention to the matter 
of dispersion. It seems to be the first instinct of many species that 
have been imported to spread widely. Therefore, if the colony put 
out be a small one the individuals composing it spread rapidly 
beyond nil means of meeting arid of mating, and thus the colonies in 
man;, instances were lost. By rearing in the laboratory, however^ 
until colonies of at least a thousand are to be had, such colonies 
