PARASITES HIBERNATING IN BROWN-TAIL WEBS. 273 



in the matter of preventing the escape of the caterpillars, but aside 

 from that, the experiment promised to be highly successful. Instead 

 of losing track of the parasites immediately following their liberation, 

 they were found to be present in abundance in and about these cages 

 throughout May and June, and even in July Mr. Mosher (who con- 

 ducted this work) observed a few alive and apparently waiting until 

 the next generation of hibernating caterpillars would be open to their 

 attack. 



Not all of the Pteromalus brood was liberated in this manner, but 

 a part of the artificially infested nests was placed in cold storage at 

 a constant temperature of approximately 30° F. and kept during the 

 summer and until the formation of the brown-tail moth nests in the 

 fall. Then a part of them was removed as a check on the condition 

 of the remainder, and when it was certain that many, if not most of 

 the Pteromalus had survived, a considerable number of them was 

 allowed to issue in the open in a locality where they would find an 

 abundance of fresh nests of the brown-tail moth ready at hand. 

 Others of the stored Pteromalus were held for the purposes of winter 

 reproduction, in case the further colonization of the parasite seemed 

 worth attempting. 



At first it appeared that the colonies of 1903, both spring and fall, 

 were successful. In the vicinity of each of them (but particularly of 

 that which was planted in the fall) the larvae of the parasite were 

 found in the nests of the brown-tail moth, and for the first time it 

 was known to have lived over summer out of doors. Extensive rearing 

 work was organized in the laboratory, with the intention of securing 

 at least 1,000,000 for colonization in 1909, and certain technical inves- 

 tigations into the life of the parasite, which were begun in the spring 

 of 1908, were continued. 



The results of these biological investigations soon became startling 

 in their nature. Gradually, as they were continued, and the results 

 of one experiment after another became apparent, a tale of insect 

 duplicity was unfolded the like of which has never been quite equaled 

 in any similar investigation. It is not possible to give the story in 

 anything like complete detail, but a brief summary ought to be pre- 

 sented, if for no other purpose than to illustrate the degradation to 

 which a parasite may sink. 



It was found that the instinct of the female Pteromalus was first 

 to seek the immediate vicinity of the feeding caterpillars, or of the 

 nests or molting webs which they had deserted, and second to ovi- 

 posit upon nearly anything which she encountered, providing it 

 resembled in the slightest degree a dormant caterpillar of the brown- 

 tail moth inclosed in its hibernating web (fig. 66). Attempted 

 oviposition upon active caterpillars was only one of innumerable 

 95677°— Bull. 91—11 18 



