PARASITES HIBERNATING IN BROWN-TAIL WEBS. 283 



hoped to secure 10 times that number at the very least. The few 

 that were reared were placed in the field in accordance with the pro- 

 gram mapped out the winter before, just about the time when the 

 new generation of brown-tail caterpillars was beginning to construct 

 winter nests, and when there was no possible excuse for failure on the 

 part of the Apanteles to reproduce to the full extent of its powers. 

 In so far as the puny colony thus planted could possibly be expected 

 to succeed, this one was a success. Quite a number of cocoons was 

 found the next spring in the molting webs of the caterpillars from 

 the near-by nests, and it was evident that if the Apanteles had been 

 reared as successfully at this season of the year as it had been hoped 

 would be the case, no better plan for the rearing and colonization of 

 the species could be devised. 



There was no possibility of judging the success or failure of the 

 Apanteles colonies of 1908 until the following spring at the earliest, 

 and whether they succeeded or failed it was obviously desirable to 

 continue the work at least one year more. Accordingly, more nests 

 were imported in the winter of 1908-9, and from among them those 

 which were the most highly parasitized were selected for rearing 

 the Apanteles. No attempts to establish colonies out of season were 

 made this time. 



Partly as a result of experience gained the year before, partly 

 because more caterpillars were fed, and partly because several among 

 the lots of nests received this year were very heavily parasitized, the 

 number of Apanteles reared and colonized was about 23,000, or twice 

 the number of the year before. They were distributed in three colo- 

 nies, one of which was near the site of the only successful late spring 

 planting of 1908. There was no apparent necessity for this, but the 

 accuracy of the theory of the large colony and establishment at any 

 cost was becoming more and more evident, and it was resolved to let 

 no opportunity slip by which a possible advantage might be lost. 

 The two remaining outlying colonies were each as large as the suc- 

 cessful colony of 1908, and Apanteles was recovered in the spring of 

 1910 in the vicinity of both. 



By the spring of 1909 the pteromalid, which had commonly been 

 reared from the Apanteles cocoons, was identified beyond question as 

 Pteromalus egregius. It was found that the females persistently 

 haunted the trays in which the caterpillars were feeding, and that 

 they were very free in ovipositing in the cocoons of Apanteles when- 

 ever they encountered them. It was discovered, furthermore, that 

 if the weather was hot and humidity low, the Apanteles larva or pupa 

 in the cocoon attacked would die and dry up before the Pteromalus 

 was full-fed, so that nothing would emerge. A few of the unhatched 

 cocoons, of which there were more than 25 per cent in the summer of 

 1908, were saved and examined after these facts were known, and in 



