NARRATIVE OF PROGRESS OF WORK. 61 



on the northwest, and from the Pyrenees on the southwest to the 

 shores of the Baltic on the northeast. In spite of the voluntary 

 assistance of such men as Rene Oberthur and Josef Jablonowski, the 

 expense of getting these nests to Boston had been very considerable, 

 and the moment when this examination was begun was considered 

 to be rather a critical one. No published record of the rearing of 

 parasites from these winter nests was recalled by the senior author 

 or by any of his European correspondents, and the expensive experi- 

 ment rested solely on the unpublished observation of Jablonowski, 

 and he himself had simply seen parasites emerge from nests in the 

 spring. Would they prove useless ? Had the parasitic insects, even 

 if useful, simply crawled into the nests for hibernation ? Or were they, 

 some of them, true parasites of the young larvae ? Representative nests 

 were examined from a number of different localities, and the relief 

 and joy were great when parasitic larvae were found in considerable 

 numbers in each of the nests examined, feeding within the nest pockets 

 externally upon the brown-tail larvae. This particular experiment 

 was a success, and the expenditure of money and trouble was justified. 

 About April 25 these parasites began to issue from the nests. The 

 nests had been gathered in all from 33 different localities, and from 

 some of them only a small number of parasites was reared. In all, 

 about 70,000 issued, of which about 8 per cent were hyperparasites. 

 In the rearing cages above mentioned it was a comparatively easy 

 matter for Mr. Titus to separate the hyperparasites from the true 

 parasites and to destroy the former. Of the species issuing in that 

 spring — and they continued to issue until about June 15 — there were 

 two species which appeared to be important, namely Pteromalus 

 egregius Forst. and Habrobracon brevicornis Wesm. The latter species 

 proved later to have entered the nests for hibernation only. 



With the cooperation of Mr. Kirkland, several localities were found 

 in which there was slight danger of forest fire and in which no work 

 against the moths would apparently be undertaken for at least some 

 months to come, and colonies of various sizes — the three principal 

 ones including, respectively, 10,000, 15,000, and 25,000 parasites — 

 were liberated in the open. Outdoor cages had been built over trees, 

 and some smaller colonies of the parasites were placed in these cages. 

 Both the outdoor experiments and the open experiments were 

 seriously hampered, however, by the fact that the season proved to 

 be one of extraordinary humidity, which caused the appearance of a 

 fungous disease which destroyed a large proportion of the brown-tail 

 moth larvae in the vicinity of Boston. 



Coincident with the issuing of these parasites from the nests, as the 

 season grew warm the young larvae swarmed from the nests and 

 filled the glass tubes in the breeding cages and were constantly being 

 destroyed by the assistants in the laboratory, and when the parasites 



