RATE OF INCREASE OF GIPSY MOTH. 
109 
In effect, the proposition is here submitted as a basis for further 
discussion that only through parasites and predators, the numerical 
increase of which is directly affected by the numerical increase of 
the insect upon which they prey, is that insect to be brought under 
complete natural control, except in the relatively rare instances in 
which destruction through disease is not dependent upon super- 
abundance. 
The present experiment in parasite introduction was undertaken 
and has been conducted on the assumption that there existed in 
America all of the various elements necessary to bring about the 
complete control of the gipsy moth and the brown-tail moth, except 
their respective parasites. Believing that this stand was correctly 
taken, much time has been devoted to a consideration of the extent 
to which these pests are already controlled through natural agencies 
already in operation. The fact that both insects have increased 
steadily and rapidly in every locality in which they have become 
established and where adequate suppressive measures have not 
been undertaken, until they have reached a stage of abundance far 
in excess of that which prevails in most countries abroad, renders 
superfluous further comment upon the present ineffectiveness of 
these agencies. The difference between the rate at which they 
have averaged to increase in localities where they have become 
established and their potential rate of increase as indicated by the 
number of eggs deposited by the average female should indicate 
very accurately the efficiency of such agencies, and the difference 
between the actual rate of increase and no increase similarly indicates 
the amount of additional control which must be exerted by the para- 
sites if their numbers are to be kept at an innocuous minimum. 
THE RATE OF INCREASE OF THE GIPSY MOTH IN NEW ENGLAND. 
The potential rate of increase as determined by the number of 
eggs deposited by the average female of the gipsy moth varies con- 
siderably under different circumstances, and affords an interesting 
example of a phase of facultative control not touched upon in the 
last chapter. When the exhaustive studies into its life and habits 
were conducted under the general supervision of the Massachusetts 
State Board of Agriculture during the final decade of the last century, 
it was determined that the number was between 450 and 600. 
In the opinion of some, the fecundity of the gipsy moth has dis- 
tinctly decreased during the 14 years which have elapsed since the 
publication of the report in which these figures were given, and in 
order to determine the point a considerable number of egg masses 
was collected during the winter of 1908-9 and the eggs carefully 
counted. It was found that in those from the older infested terri- 
tory or from outlying colonies where the moth was particularly 
