284 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 



several of them what were almost certainly the eggs and very young 

 larvae 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 larvae 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 XXVI, 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 

 a re good that it will replace them to a certain extent, without bringing 

 about 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. 



