294 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 



became certain that no shipments of any consequence would be 

 received. 



It was known that the parasite could be secured in this manner 

 because small numbers had been reared from the imported quantities 

 of full-fed and pupating caterpillars which were received at the labo- 

 ratory in 1906 and several hundred from similar shipments in 1907. 

 This latter year no accurate records had been made of the number of 

 each species of tachinids emerging from the importations of brown-tail 

 moth material, but it was known that somewhere between 300 and 500 

 individuals had been reared, the most of which were colonized at North 

 Saugus. This was the only lot of adult flies of any consequence which 

 had been reared and liberated, and since special efforts which had been 

 made to recover this and other species liberated at the same time and 

 place had failed in both 1908 and 1909, it was not considered to be at 

 all likely that the attempted colonization was successful. 



The situation, in so far as Zygobothria was concerned, could hardly 

 have appeared worse than it was at the beginning of July, 1910. Xo 

 one species of anything like equal importance had been quite so diffi- 

 cult to secure in adequate numbers and, moreover, there was no imme- 

 diate prospect of finding a way to overcome the difficulties attending 

 its importation. Consequently no similar circumstance, except per- 

 haps the recovery of the gipsy-moth parasite, Apantelesfulvipes, could 

 have caused a livelier satisfaction than was felt when several bona fide 

 specimens of Z} r gobothria were reared from a lot of cocoons of the 

 brown-tail moth which had been collected in the field some time be- 

 fore. The first specimen to issue was a male and it was followed by 

 several more of the same sex. The males are markedly different from 

 the females in appearance and not quite so distinctive, and we did not 

 feel absolutely sure of their identity at first, but when after a few days 

 a female was secured in the same manner from American cocoons 

 there was no possible doubt that the species was not only established 

 in America as firmly as three generations from a small beginning 

 would permit, but dispersing with considerable rapidity, since of the 

 seven specimens reared none was from less than 1 mile of the original 

 colony site and one was from at least 3 miles distant. It is certain 

 that the species must have spread over at least 30 square miles since 

 its colonization three years ago, and when the millions of brown-tail 

 moth caterpillars which are present in that territory are compared 

 with the few thousands which produced the seven Zygobothria reared 

 in 1910, it is equally certain that its increase has been at the same 

 time enormous. 



It bids fair, judging from this, to do exceedingly well in America. 

 Unlike Compsilura concinnata, Pales pavida, and other tachinids, which 

 rank of some importance as parasites of the brown-tail moth and gipsy 

 moth in the Old World, it is wholly independent of any host other 





