GYPSY AND BROWN-TAIL MOTHS. 13 



gross numbers any list of parasites of the gypsy moth which 

 has ever been published. One by one, as these parasites have 

 been received and studied, they have been rated according to 

 their habits and importance in the countries from which they 

 came, and those which have failed to show promise of ever 

 becoming of value in America have been eliminated. One by 

 one, different species have been liberated in America under the 

 most favorable conditions which could be provided for their 

 establishment, until at the present time there are only 3 or 4 

 out of a total of 20 (which may be considered as including all 

 of the promising parasites of the gypsy moth in Europe and 

 Japan) which have not been liberated here, or which are not on 

 hand ready for liberation as soon as the proper season shall ar- 

 rive. The others, tentatively considered as of possible value, 

 are very rarely common in any country; and partly on this 

 account, and partly on account of the extraordinary difficulties 

 which stand in the way of their successful importation, it has 

 been impracticable to determine whether they are to be ranked 

 as promising, or not. It is very likely that they will prove to be 

 of a distinctly minor importance when they shall have been 

 thoroughly investigated. 



SEQUENCE OF PARASITES. 



There is one very important factor which must be taken into 

 consideration and thoroughly understood before it will be pos- 

 sible intelligently to discuss the work which has been accom- 

 plished in the importation of parasites of the gypsy moth. 

 Briefly stated, it is that no one parasite is capable of effecting 

 the necessary amount of control in an insect of the character of 

 the gypsy moth, and capable of a similarly rapid rate of increase 

 when unchecked by parasites ; but a sequence of parasites, which 

 will attack the insect in different stages of its development, and 

 all the component members of which will work together in har- 

 mony, is absolutely necessary before the best results may be 

 expected. 



It has already been stated that the different parasites of one 

 host are limited in their attack to certain stages in the develop- 

 ment of this host. In the case of the gypsy moth, there are 

 some which attack the egg, others the young caterpillars or the 



