306 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 
may depend upon the establishment, not of the most important 
among the parasites and other natural enemies, but of a group or 
sequence of species winch will work together harmoniously toward 
the common end. Viewed in this light, the importance of parasites 
which otherwise might be considered as of minor interest is greatly 
enhanced. 
It is impracticable to determine certain facts in the life and habits 
of those parasites which have been colonized under conditions 
believed but not known to be satisfactory. Further detailed knowl- 
edge is necessary before we can judge whether the circumstances sur- 
rounding colonization were in truth the best that could be devised. 
Furthermore, so long as original research is confined to the study of 
materia] collected by foreign agents, some of whom are technically 
untrained, it is practically impossible to secure the evidence necessary 
to refute published statements concerning the importance of certain 
parasites abroad which the results of first-hand investigations have 
not served to confirm. It is believed that these statements are 
largely based upon false premises, but should this belief prove un- 
grounded it would mean that there are important parasites abroad 
of which little or nothing is known first-hand. 
A determined effort was made in 1910 to better the deficiencies in 
the foreign service without going to the lengths of adopting a radically 
changed policy, but the results were not satisfactory. Lack of 
assurance that a continuation of the work in 1911 along similar lines 
would bring more favorable results made its continuation inadvisable. 
It therefore became a question of adopting new and radically different 
methods in so far as the foreign service was concerned. 
In favor of a policy of inactivity was the prospect of an imme- 
diate reduction, as opposed to an increase, in expenditures should 
renewed activity be decided upon. There was the chance that the 
parasites already introduced and colonized would be sufficient to 
meet the demands of the situation. 
On the other hand, the vast majority of defoliating native insects, 
which rarely or never become so abundant as to be considered injuri- 
ous, prove upon investigation to support a parasitic fauna similar 
in all its essential characteristics to that supported by the gipsy 
moth in countries where it is similarly a pest at very rare intervals 
or not at all. 
Parasitism appears to be unique among the many factors of con- 
trol, in that no other agency similarly increases in efficiency in direct 
proportion as the efficiency of other agencies, such as climatic con- 
ditions, miscellaneous predators, etc., diminishes. In short, the 
apparent importance of parasitism as a factor in the natural control 
of defoliating insects has been decided!} enhanced as a result of 
these more or less technical and intensive studies. It can be said 
