TACHINID PAKASITES OF THE GIPSY MOTH. 223 



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. 



