268 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 



brown-tail moth, or to the larvae or pupae of the parasite, indiscrimi- 

 nately, and in some of the reproduction cages practically every host 

 and parasite had been attacked. 



It was not known where these mites came from, but it was pre- 

 sumed that they were brought in from the field upon nests of the 

 brown-tail moth. By the time that they had been discovered they 

 were in practically everything in the laboratory. Even tachinid 

 puparia were not immune to attack, and there were numerous 

 instances in which the wandering young had forced their way through 

 tight cotton plugs, which would ordinarily have prevented the pas- 

 sage of bacteria. 



Much time and trouble was necessary before the laboratory was 

 finally cleared of the pest; but it was finally accomplished by the 

 rigid separation of every rearing cage containing life which had 

 been present before the invasion became apparent from those which 

 were begun afterwards. The general cleaning up and policy of seg- 

 regation proved effective, and by spring the last of the mites appeared 

 to have died; nor has a single specimen been observed since. 



As parasites of the brown-tail moth the mites were singularly effec- 

 tive. If it were possible to bring about a general infestation of the 

 nests in the early fall, it would doubtless result in the destruction of 

 a very large proportion of the hibernating caterpillars; but unfortu- 

 nately this seems to be not at all practicable. It is not even certain 

 that the parasite was actually brought into the laboratory in nests 

 of the brown-tail moth, though this would seem to be the most likely 

 explanation of its presence. 



The fact that its presence has never once been detected in any of 

 the many thousands of similar nests which have been brought in at 

 other times indicates rather conclusively that it is not actually an 

 enemy of any consequence in the field. 



PTEROMALUS EGREGIUS FORST. 



It was quite late in the spring of 1905 before the senior author was 

 able to organize a corps of European collectors, and as a consequence 

 only a very small quantity of parasite material was imported during 

 the summer of that year; but during the fall and winter following, 

 well within a year after the work was first authorized by the Massa- 

 chusetts Legislature, importation was begun in earnest. More than 

 100,000 hibernating nests of the brown-tail moth were received from 

 abroad that winter, and since scarcely anything was surely known 

 of the parasites which were likely to be reared from them, the early 

 discovery of the hibernating brood of Pteromalus egregius (fig. 60, 

 p. 263) was hailed with satisfaction. The circumstance has already 

 been the subject of comment in an earlier section. 



