72 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 



den, the junior author was able to carry out some new ideas with 

 admirable results. The first of these was the carrying on of active 

 winter work with parasites, especially those secured from the imported 

 nests of the brown-tail moth, which began to come in from Europe 

 in December. It was found quite possible to rear these parasites 

 in artificially heated rooms, feeding them upon hibernating native 

 brown-tail larvae brought in in their nests from out of doors, feeding 

 the latter upon lettuce and other hothouse foliage, and in the early 

 spring securing more normal food for them by sending it up in boxes 

 by mail from Washington and points south. In this way the rear- 

 ing of the parasites of the genus Pteromalus was carried forward 

 uninterruptedly throughout the winter, and, as during the rearing of 

 successive generations they multiplied exceedingly, it was possible 

 later in the year to liberate a vastly greater number of individuals 

 than had the imported species been allowed to hibernate normally in 

 the nests. In the course of this work the junior author invented a 

 rearing tray which was of the utmost advantage and which has since 

 greatly facilitated parasite rearing work. This tray will be described 

 later. 



With the importation of brown-tail moth eggs it often happened 

 that they hatched too soon to be of use in America; or too late, 

 arriving after the American eggs had all hatched. It was ascertained 

 by the junior author during the summer and aatumn that native eggs 

 can be kept in cold storage until the arrival of the European egg 

 parasites, which were found to lay their eggs and breed in these cold- 

 storage eggs as freely as in those which they attack in the state of 

 nature. It was found that this process can be carried on for a long 

 time, and that successive generations of these egg parasites may be 

 reared from eggs retarded in their development by cold storage. It 

 was thus shown that it is easy to rear and liberate an almost 

 infinitely greater number of these egg parasites, and under favorable 

 conditions, than would have been possible from a simple importation 

 of European parasitized eggs which would have to arrive in America 

 at a specific time. 



In the same way great advance was made in the rearing of the 

 tachinid parasites in Mr. Townsend's charge. This expert devised 

 methods and made observations that greatly added to our knowledge 

 of the biology of these insects and resulted in the accumulation of a 

 store of information of the greatest practical value, not only in the 

 prosecution of the present undertaking but in any problem of parasite 

 introduction or control that may arise later. Extraordinary and 

 almost revolutionary discoveries were made in the life histories of 

 certain of these flies, and without this knowledge the greatest success 

 in handling them practically could not have been reached. Certain 

 of these facts regarding the most important of these parasites are 



