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. No 
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, Apanteles fulvipes, could 
have caused a livelier satisfaction than was felt when several bona fide 
specimens of Zygobothria 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 
