EXTENT OF GIPSY-MOTH PARASITISM ABROAD. 
117 
greater rate of increase than sixfold would have to be met and offset 
before the much-to-be-desired consummation could reasonably be 
expected the prospects looked rather discouraging. Recognition 
of the correlation which existed between increased abundance and 
rate of increase served more than anything else to allay the doubts 
which these reflections created. Field work in 1908, 1909, and 1910 
showed pretty conclusively that a rate of increase of not in excess of 
sixfold and possibly considerably less prevailed whenever the moth 
was in that state of innocuousness incident to the scarcity which 
it was hoped to bring about and maintain through the introduction of 
the parasites. An aggregate parasitism of So per cent will almost 
certainly be sufficient, and it may well be that SO per cent or even 
75 per cent will answer equally well. Much less than 75 per cent will 
probably not be effective. 
THE EXTENT TO WHICH THE GIPSY MOTH IS CONTROLLED 
THROUGH PARASITISM ABROAD. 
While it is true that the work which has been done for the purpose 
of determining the prevailing rate of increase of the gipsy moth in 
America leaves considerable to be desired in the way of exactness, in 
the main the statements made by Korbush and Fernald, as confirmed 
and modified by later observation, may be accepted as essentially 
accurate. It is fortunate that the situation ifi Q0 worse than it appeal's 
to be, for if it wore necessary to undertake the work of parasite intro- 
duction with the idea that the maximum rale of increase exhibited by 
the gipsy moth must be met by the parasites, such an unreasonable 
percentage <>f parasitism would be demanded as to make the propo- 
sition of Introducing them a decidedly difficult task. As it is, there 
seems to be good reason to believe that a parasitism amounting to 
7") per cent will be sufficient, provided that it can be maintained 
during the periods when the moth is relatively rare. It may be 
that less than that will answer equally well, but it would require 
actual test or else a much more careful study of the actual rate of 
increase of the moth under favorable conditions to justify such 
prophecy. In any event, 85 percent will probably be amply efficient, 
if it can be established and maintained during all stages in the abun- 
dance of the moth. Such a rate would undoubtedly prevent the moth 
from increasing to destructive abundance in new territory or from 
gaining ground lost through the activities of disease in older infested 
regions. 
Granted that it is sufficient, the question naturally arises as to 
whether such a degree of parasitism is to be found abroad in coun- 
tries where the gipsy moth is present without being considered as a 
serious pest. 
