270 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 



them was liberated in the spring of 1906, but it was later discovered 

 that, like Monodontomerus, they merely sought the hibernating nests 

 for the protection which was thus afforded during the winter. One 

 colony of Monodontomerus was also established early in the spring 

 of 1906, but almost immediately thereafter the action was regretted 

 on account of the doubts which Dr. Ashmead expressed concerning 

 the host relations of this species. ' He was certain that it was a para- 

 site of Diptera, and that it could not be a primary parasite of the gipsy 

 moth or of the brown-tail moth. As events have since abundantly 

 proved, he was right and wrong at one and the same time. 



The separation of the parasites from the exceedingly large number 

 of caterpillars which issued coincidently, and the subsequent sepa- 

 ration of Pteromalus from the remaining species, was a task of huge 

 proportions, but eventually it was accomplished, and some 40,000 

 Pteromalus were liberated in several localities, as indicated on the 

 accompanying map. At the same time an attempt was made to deter- 

 mine the habits of the species, and reproduction experiments were 

 conducted, using the active caterpillars of the brown-tail moth as 

 hosts. 



The females were frequently observed to take peculiar interest in 

 these active caterpillars of the brown-tail moth. They would fre- 

 quently alight upon their backs and appear to oviposit, and since 

 nothing was then known or suspected of the well-nigh total depravity 

 of this species in so far as its habits of oviposition are concerned, it was 

 only natural to suppose that it was really possible for successful ovi- 

 position to take place under these circumstances. Nothing less was 

 expected than that there would prove to be a second generation of 

 the parasite, developing within the active caterpillars, or perhaps in 

 the pupge. 



Attempts to discover some trace of this generation were futile, but 

 failure could not altogether be attributed to the fact that such a 

 generation did not exist. As it happened, every one of the several 

 colonies of the parasite was situated within a territory to the north- 

 ward of Boston over which the brown-tail moth was exceedingly 

 abundant. Late in the spring the host of caterpillars was suddenly 

 destroyed by an epidemic of a fungous disease which was so complete 

 and overwhelming as to leave very few survivors. Even now, four 

 years later, the brown-tail moth has not reached its former abundance 

 over a considerable portion of the territory affected, notwithstanding 

 that there has been steady and fairly rapid annual increase through- 

 out this period. It looked, in fact, as though the parasites had suffered 

 to an even greater extent than their hosts (since they were not so 

 thoroughly well established) , and failure to recover Pteromalus from 

 the field during the summer, or even during the winter following, was 

 thought to be the result of the epidemic of disease. 



