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 pupe. 
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. 
