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 autumn that native eggs 
can be kept in cold storage until the arrival of the European egg 
parasites, which were found to la} r 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 1 land ling them practically could not have been reached. Certain 
of these facts regarding the most important of these parasites are 
