PARASITES HIBERNATING IN BROWN-TAIL WEBS. 281 



ment could not be looked upon as a feasible method for obtaining the 

 parasites for liberation, and all ideas of laboratory reproduction work 

 on a large scale were regretfully abandoned before the spring was far 

 advanced. 



A program for the colonization of Apanteles during the year 1908 

 was definitely formulated as the direct result of this experimentation, 

 by which it was hoped to afford the parasite the best possible oppor- 

 tunity for speedy establishment. In accordance with this plan the 

 nests which had been found to contain the more highly parasitized 

 caterpillars were divided into three lots. The larger of these was 

 placed in the same form of tube cage which was used for the 

 Pteromal us-rearing work in 1906 and 1907; the next larger was 

 placed in cold storage, and the nests remaining were brought into the 

 laboratory toward the end of March and the caterpillars forced into 

 premature activity. There was not very much room available for 

 this indoors, so that the number of nests thus treated was decidedly 

 limited, but from the caterpillars issuing from them no less than 

 2,000 Apanteles cocoons were secured during the latter part of April, 

 and the adult Apanteles, to the number of about 1,300, which issued 

 from them were liberated in the one colony in the field just as the 

 caterpillars of the brown-tail moth were issuing from their nests and 

 beginning to feed out of doors. 



It was known that under natural conditions the parasite never 

 issued as an adult at this season of the year, but it was reasonably cer- 

 tain that it would immediately reproduce upon the small caterpillars 

 which in a week or two more would be so large as to make reproduc- 

 tion impossible. It was hoped in this manner to give the individuals 

 liberated in this colony a certain advantage over those liberated later 

 by allowing them superior opportunities for immediate reproduction 

 and incidentally an opportunity for one more generation during the 

 year than would be possible in colonies established at a later date. 



To a certain extent these expectations were realized. It was posi- 

 tively ascertained that the parasite did take advantage of the oppor- 

 tunity offered and that it did actually pass one generation upon the 

 newly active caterpillars of its chosen host. The experiment is not 

 known to be a practical success, however, because all subsequent 

 attempts to recover Apanteles from nests of the brown-tail moth 

 collected in the vicinity of this colony have failed. 



As soon as the caterpillars in the nests which had been placed in 

 the large cages became active they were transferred to the larger 

 trays which had been provided especially for them (PL XXVI, fig. 2), 

 and fed first with lettuce and later with fresh foliage collected in the 

 field. They did remarkably well at first, and about May 20 the 

 cocoons of Apanteles began to appear in the trays in large numbers. 

 The collection of these cocoons and their removal to small cages for 



