284 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 
several of them what were almost certainly the eggs and very young 
larvee of Pteromalus were found. It thus became evident that at 
least a portion of this unfortunate mortality was due to hyper- 
parasitism by Pteromalus, a considerable number of which had been 
free in the compartment where the caterpillars of the brown-tail moth 
had been feeding. In 1909 pains were taken to prevent a recurrence 
of these circumstances, and as a result only a very few of the cocoons 
were lost through attack by Pteromalus. That Pteromalus was to be 
considered as an aggressive enemy of Apanteles could no longer be 
doubted, and when it was remembered that the adults naturally 
emerged from the nests of the brown-tail moth in the open at almost 
the precise time (Pl. XXVIII, fig. 1) when the Apanteles larvee were 
emerging and spinning their cocoons, more often than otherwise in 
the outer interstices of these same nests, and that, furthermore, the 
Pteromalus was prone to linger in the vicinity of these nests in prefer- 
ence to any other place, its true duplicity was at last realized. 
A much smaller number of over-wintering nests of the brown-tail 
moth was imported during the winter of 1909-10 than during any 
other since the beginning of the work, more for the purpose of securing 
Zygobothria, if possible, than for the rearing of additional Apanteles. 
The large trays were used as before (Pl. X XVI, fig. 2) for the rearing 
of a number of the caterpillars in the spring, and 10,000 or more 
Apanteles were reared and liberated in one colony at some distance 
from any of the others. 
Until late in the summer of 1910 considerable doubt was felt as 
to the ability of this Apanteles to pass through the summer months 
successfully in large numbers. That it was able to live from June to 
August or September at all was rather more than was expected when 
it was first liberated. When, in 1908 and 1909, it proved its ability 
to do that much it remained to be determined whether it was going to 
be dependent upon an alternate host during that period or not, and 
if dependent whether a sufficient abundance of such hosts would be 
found in America to support as many of the parasites as would needs 
be carried through the summer, if it were to become an aggressive 
enemy of the brown-tail moth when this insect is in abundance. 
It was with much satisfaction, therefore, that Apanteles lacteicolor 
Vier. was recovered as a parasite of Datana and Hyphantria late in the 
summer of 1910. Both hosts are common at that season of the year 
in Massachusetts, and both are parasitized to a considerable extent 
by tachinids. It is certain that the Apanteles will develop at the 
expense of these parasites as well as that of their hosts, and the chances 
are good that 1t will replace them to a certain extent, without bringing 
«bout a serious reduction in the prevailing abundance of these hosts; 
in short, that it will find a permanent place for itself in the American 
fauna. 
