TACHINID PARASITES OF THE GIPSY MOTH. 293 
had pupated and remained alive. The remainder had died, principally 
as the result of parasitism. 
In all 96 tachinid puparia and 1 cocoon of Meteorus were found. 
Of these puparia 95 were Compsilura concinnata and the other 
apparently Tachina mella. The Meteorus, incidentally, proved to 
be of the introduced species, Meteorus versicolor. 
Parasitism by native tachinids was probably considerably higher 
than would be indicated by the fact that only a single puparium 
was secured as against 95 of the imported species, but because the 
latter completes its larval development much more rapidly than 
does Tachina mella, it would almost certainly be the victor in case 
of a conflict. 
Later collections of tussock-moth caterpillars made for the express 
purpose of determining the limits to the distribution of Compsilura 
resulted in its discovery throughout practically all of greater Boston, 
and it may be that it will have some effect in reducing the importance 
of this insect as a pest in that city and its suburbs. With the end 
of experimenting further along this line the puparia secured from 
the Lynn collection, together with several hundred more from gipsy- 
moth caterpillars, were sent to Washington, where they were liberated 
upon the grounds of the Department of Agriculture, where the tussock 
moth is periodically a pest. 
Another indication of good which may possibly result from the 
introduction of this tachinid resulted from an investigation, begun in 
September, 1910, by Mr. J. D. Tothill, into the parasites of the imported 
cabbage butterfly ([Pieris] Pontia rapx L.). He found that in locali- 
ties where Compsilura was known to be common the summer before, 
it was actually abundant as a parasite of this pest, and as high as 40 
per cent had been attacked in some instances. 
There is no native tachinid known to have quite the same habits 
as Compsilura, neither is there any with quite so varied a list of 
hosts. Both the cabbage butterfly and the tussock moth are com- 
monly considered as pests, the one generally and the other in cities, 
and both can probably sustain additional parasitism without much 
difficulty. - But in the case of the other native insects liable to attack 
by the imported parasite, and already thoroughly well controlled by 
various agencies, of which parasitism is one, the outcome of the 
struggle which is likely to ensue is probably going to be different. 
In the case of such an one it is reasonably safe to predict that one of 
two things will happen. Either the prevailing abundance of the 
host will be reduced through the introduction of a new factor into 
its natural control, or the host will maintain its present relative 
abundance, and its parasites will suffer directly in the struggle into 
which they will be forced by the advent of the tachinid. 
