TACHINID PARASITES OF THE GIPSY MOTH. 221 



Hardly was the final establishment of what was for a few days 

 considered to be the first satisfactory colony of Compsilura concin- 

 nata accomplished than the necessity for the expenditure of further 

 labor on its account was obviated by the discovery that it could be 

 recovered from the field in small but at the same time in very satis- 

 factory numbers. Only an insignificant number was reared from the 

 collections of gipsy-moth caterpillars made in 1909, but later in the 

 fall of that year field men who were scouting for evidences of the 

 spread of Calosoma and searching under burlap bands for its molted 

 larval skins began to bring into the laboratory bona fide'puparia of 

 Compsilura found under the same circumstances. It was thus pos- 

 sible to delimit its range with some accuracy, and it was found to 

 extend over a considerable territory, with the 1906-7 colony in 

 Saugus much nearer to its center than any other more recently 

 located colony. (See fig. 42.) There could be no doubt that the 

 species was well established and spreading and multiplying at a rapid 

 rate. 



The results of the season of 1910 were awaited with very great 

 interest, in expectation that they would confirm those of the year 

 before. That these were confirmed, and most conclusively and 

 satisfactorily, is evidenced by the results of the rearing work as 

 summarized in Tables IV and V (pp. 141, 142), which give the 

 results of rearing work for that year. The total number of the 

 parasites reared or otherwise recovered from the field as indicated 

 by these tables is very far short of the total secured. 



Compsilura concinnata is recorded as a parasite of a large number 

 of hosts in Europe, and will doubtless be found to attack an equally 

 large number in America when it shall have become thoroughly 

 established and abundant over a wide territory. Already some half 

 dozen native hosts are known, and it would easily be possible to 

 double or treble this list in the course of another season's work, 

 should it be conducted with that end in view. 



Few subjects for speculation are so overcrowded with possibilities 

 as that of the effect which the importation of new parasites having 

 a wide range of hosts will have upon native parasites and their hosts. 

 The increasing abundance of Compsilura offers a most excellent 

 opportunity to answer numerous questions which naturally arise 

 when this subject is considered, and it is hoped that it may be made 

 the most of. Already several highly significant observations have 

 been made. 



One of the most interesting of these resulted from a series of col- 

 lections of tussock-moth caterpillars made by Mr. Wooldridge in 

 the summer of 1910 for the purpose of determining the prevalence 

 of parasitism in various localities and under slightly different condi- 

 tions. All of these collections were of necessity made under urban 



