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 



