10 . IMPORTED PARASITES. 



-for the destruction of a tremendous percentage. Eive hundred 

 eggs, developing into an equal number of males and females, 

 would result in the deposition of 250 egg masses the summer 

 following, or an increase of two hundred and fifty-fold. If 

 only a six-fold increase in the number of egg masses results, it 

 is evident that 244 of the females must be destroyed at some 

 time during their life; in other words there is an approximate 

 mortality of no less than 97.6 per cent, annually in Massachu- 

 setts, due to natural causes. 



So, to reduce the number of survivors as to permit of no an- 

 nual increase, on the average, in territory where the gypsy moth 

 is not sufficiently abundant to become a pest, is the hope and 

 aim of the work of parasite introduction. As already stated, 

 there is no steady increase of the moth in the central most 

 badly infested sections of the area of infestation ; but the control 

 brought about by famine and plague within this area is so ex- 

 clusively dependent upon overpopulation, which is to say, upon 

 a superabundance of the moth, as to make very probable a con- 

 tinuation of the present conditions for an indefinite period, un- 

 less some other factor becomes operative. 



PARASITE INTRODUCTION IN THEORY AND PRACTICE. 



If, as is believed by those who have the matter most at 

 heart, the only important controlling agency which is lacking in 

 America is the presence of the parasites which are such effective 

 factors in its control abroad, the introduction of these parasites 

 into America and their establishment here is all that is neces- 

 sary to bring about the reduction of the gypsy moth from its 

 present pre-eminence as a destructive pest to that of an innocu- 

 ous or rarely noxious insect. The problem at first sight seems 

 simple, but, like most undertakings, it develops complications in 

 its practical solution. 



Long before the work of parasite introduction was begun, all 

 of the published records of European parasites and other ene- 

 mies were well knoMm to the Bureau of Entomology, which for 

 years had been keeping track of such observations, and had ac- 

 cumulated a card catalogue with more than 20,000 references. 

 As soon as work was begun, additional information concerning 

 gypsy and brown-tail parasites was secured from European and 



