220 PARASITES OF GTPSY AND BROWN-TAIL MOTHS. 



would have been reared before now from some among the hundreds 

 of thousands of brown-tail caterpillars which have been carried 

 through their first three or four spring stages in the laboratory. None 

 having been reared under these circumstances, the only logical con- 

 clusion is that they start into activity so early and develop so rapidly 

 as to cause the death of the host before they are sufficiently advanced 

 to pupate successfully. This is not necessarily the true explanation 

 of the failure to rear the species from hibernating brown-tail cater- 

 pillars fed in confinement, but it appears to be the best. 



Ordinarily in the summer the larvae do not pass over into the pupa 

 of the host, but occasionally they do so. In the late summer and 

 fall, when the host caterpillar is of a species which hibernates as a 

 pupa, the parasite appears to be aware of that fact in some subtle 

 manner, and likewise prepares for hibernation. Its larva? (or what 

 are without much doubt its larva?) have several times been found in 

 hibernating pupa? of several species. The adult has never yet been 

 reared from pupa? under these circumstances, and the record is on 

 that account open to some question. 



The larger part of the Compsilura which were imported from 1906 to 

 1908, inclusive, issued from puparia (PL XX, fig. 1) found free in the 

 boxes of brown-tail caterpillars from abroad. A companion species, 

 Dexodes nigripes, which is indistinguishable from Compsilura in any 

 of its preparatory stages, has also been reared under exactly similar 

 circumstances, but curiously enough, if Compsilura was common in 

 material from the same locality, Dexodes was apt to be rare, or vice 

 versa. Some few were reared from gipsy-moth importations during 

 this same period, but not in anything like the numbers which were 

 secured from the brown-tail moth material, and it was not considered 

 as of particular importance as a gipsy-moth parasite until 1909, 

 when it was found to be very common among the tachinid parasites 

 secured from shipments of gipsy-moth caterpillars from southern 

 France. 



The first colonies of Compsilura were planted in various localities 

 within the gipsy-moth infested area in 1906, and in 1907, according 

 to the records of the laboratory, a single fly was reared from gipsy- 

 moth caterpillars collected in the immediate vicinity of one of these 

 colonies. There is some reason to doubt the truth of this record, 

 since every attempt at recovery made in 1908 failed. 



In 1907 a much larger colony than any ever liberated before was 

 located in the town of Saugus, in the near vicinity of one of those of 

 the previous season. In 1908 none was colonized. In 1909 several 

 very large and satisfactory colonies were planted in several places 

 within the infested area, and for the first time it was felt that the 

 species had been given a fair opportunity to prove its effectiveness 

 as an enemy of the gipsy moth and brown-tail moth in America. 



