June, 10] THOMPSON : TACHIXID PUPATION 293 



but not all of the larva? of this species were affected in a definite 

 manner by hosts which pass the winter in the larval or pupal stage. 

 Such a reaction between host and parasite, if it exists, must be of a 

 most subtle and complex character, and it would be quite useless at 

 the present time to speculate upon its nature. 



It would be interesting to know whether any of the individuals 

 which, as Pantel states, "finish their larval development in some days 

 and emerge to pupate," pass the winter in the nymphal stage within 

 the puparium, which he does not clearly explain, although he remarks 

 that the pupal period varies from 13-16 days in summer, to 30-60 in 

 winter, which makes it seem probable that some of the parasites might 

 in some cases hibernate as nymphs. We have never observed such an 

 occurrence here although we have handled large numbers of the 

 puparia, which were, however, an earlier brood than the one of which 

 Pantel speaks. 



The hibernation of Frontina frenchii as a parasite of cecropia has 

 been already discussed in an earlier paper on the parasites of the 

 Saturniidse. It seems verj^ likely that this parasite often hibernates 

 in both the puparium or adult stages. As a parasite of cecropia, on 

 the other hand, it hibernates within the living pupa of the host in 

 large numbers, reaching the third larval stage and emerging to pupate 

 within the cocoon of the moth in early spring. Wliile this resembles 

 the mode of hibernation of the Tachinid parasite of Euchsetias in 

 general it is worthy of separate mention as it offers an example of 

 the change in the habits of a many-brooded species, whose life cycle 

 is ordinarily quite short, whereby it adapts itself to the conditions 

 found in a host hibernating in the pupal stage, and thus secures a 

 more advantageous method of hibernation. 



It seems likely that many species of Tachinids hibernate in the 

 adult stage. The abundance of many formes late in the autumn, many 

 of them females almost fully mature sexually, seems to indicate it. 

 We have, moreover, observed such mature females of one of the 

 European parasites studied which attempted to hibernate and this 

 when they might have deposited their eggs had they so desired. If 

 such a habit is at all common, it is more than likely that the fertilized 

 females alone survive the winter. In our researches we have always 

 found that the life of the male is shorter than that of the female and 

 that its ability to withstand adverse conditions is not so great. 



Although it is impossible to explain the variations in the hibernat- 

 ing habit which we have indicated, the general reason for their exist- 

 ence is very clear. They are evidently natural safeguards to prevent 

 the extinction of the species in that they give it more opportunities 



