246 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 



was positive, indicative of secondary parasitism, because every little 

 while the Monodontomerus would issue from tachinid puparia which 

 had been sorted out from the cocoons and pupae. Still more fre- 

 quently it was reared from puparia of sarcophagids. 



In the summer of 1908 the shipment of gipsy-moth pupae from 

 Italy, which served the purpose of establishing the status of the 

 European species of Chalcis in their relation to the gipsy-moth, 

 served also in establishing the status of Monodontomerus as a primary 

 parasite of this host. A large number of the pupae which were 

 examined was found filled with the larvae (fig. 53) or pupae (figs. 

 54, 55) of the parasite, and even when the larvae were still immature 

 and feeding there was absolutely no trace of any other parasite present 

 in the majority of instances. There was such trace in a few, and it 

 was found that the former presence of Pimpla, Theronia, or any 

 tachinid was very easy of determination, no matter how completely 

 it might have been destroyed. 



It was felt that a mistake had been made in not liberating the very 

 large number of Monodontomerus which had been secured through 

 the earlier shipments, and it was resolved to colonize them as fast as 

 they were secured in the future. Hardly anything was less expected 

 than that the species should even then be established. 



Each winter since that of 1906-7 (PL XXI) large numbers of the 

 winter nests of the brown-tail moth had been collected in a vain 

 endeavor to secure evidences of the establishment of Pteromalus 

 egregivs, but without results. In the winter of 1908-9 this work was 

 undertaken anew, and almost the first lot which was brought into the 

 laboratory was shortly productive of a number of Monodontomerus, 

 exactly as lots collected in the open in Europe had been productive 

 of the species each season since their importation had been begun. 

 The circumstance, surprising and unexpected, was also gratifying, 

 coming as it did so soon after the investigations which had served to 

 demonstrate the primary parasitism of the species. The surprise and 

 gratification was increased materially when it was discovered, through 

 the collection of a large quantity of the winter webs, that the parasite 

 was distributed over a considerable territory indicated by the area I 

 on the accompanying map (PL XXII), and though the actual number 

 recovered was small, the rapid rate of dispersion was sufficient to 

 indicate a very rapid rate of increase. It was estimated, in fact, that 

 at least a 25-fold per year increase and a 10-mile per year dispersion 

 had followed the colonization three years before. 



In 1909 an examination of the pupae of the gipsy moth in the field 

 revealed the presence of what was actually a small, but under the cir- 

 cumstances a gratifyingly large, number which contained the larvae or 

 pupae of the parasite, and the results of the winter scouting work were 

 awaited with confidence and interest. They were quite as satisfac- 



