14 



PARASITES OP GIPSY AND BROWN-TAIL MOTHS. 



England as nearly as possible the entire natural environment of the 

 gipsy moth and the brown-tail moth in their native homes, similar 

 conditions of comparative scarcity could surely be reached, and this 

 view he still holds with enthusiasm. Naturally, in the course of the 

 work as it progressed year after year his ideas have been changed as 

 to methods, and very great improvements have been made upon the 

 earlier methods, largely through the intelligence and ingenuity of 

 the junior author of this bulletin. Moreover, the careful, intensive 

 studies which have been made at the gipsy-moth parasite laboratory 

 by the junior author and a corps of trained assistants, aided by 

 abundant material, funds, and supplies, have resulted not only in the 

 ascertainment of very many facts new to science, but in the accumu- 

 lation of such facts to such a degree as to enable generalizations of a 

 novel character and of a- sounder basis than could have been had 

 under other conditions. Many points are brought out in this bulletin 

 which will doubtless be entirely new to the trained scientific reader. 

 Mistakes have been made and wrong conclusions have been drawn 

 from time to time, but these have been corrected, and we are now in 

 a fair way to see a favorable result from the long and expensive work. 



The initial idea was that since a large percentage of gipsy-moth 

 caterpillars or brown-tail moth caterpillars in Europe contains para- 

 sites each year, therefore if these caterpillars were brought to America 

 in large numbers from every possible place we could not fail to rear 

 from them an abundance of adult foreign parasites. This idea was 

 sound, and in following it out we have constantly improved the 

 methods — methods of collection, of packing, of shipment, and of 

 subsequent rearing. Very large numbers of parasites have been 

 reared. 



It was first thought that when parasites had been reared in suffi- 

 cient numbers they should be widely distributed in small colonies, on 

 the theory that each colony would remain in substantially the same 

 general locality and would increase and spread from that point. This 

 idea was a natural one and was fully justified by previous work which 

 had been done with parasites of other groups of insects, but in this 

 case it proved to be erroneous, and valuable time and valuable speci- 

 mens were lost. Eventually it was shown to be of prime importance, 

 first to establish a given species of parasite in this country, and not 

 until this has been accomplished to pay any attention to the matter 

 of dispersion. It seems to be the first instinct of many species that 

 have been imported to spread widely. Therefore, if the colony put 

 out be a small one the individuals composing it spread rapidly 

 beyond all means of meeting and of mating, and thus the colonies in 

 many instances were lost. By rearing in the laboratory, however, 

 until colonies of at least a thousand are to be had, such colonies 



