June, '10] THOMPSON : TACHIXID PUPATION 391 



to the fatty reserve material which they contain and the skin is of a 

 hard firm texture. The larv^fe in this respect resemble those of certain 

 Sarcophagids which as we have observed, are able to remain alive in 

 drj- receptacles without food for several months, owing to the im- 

 permeable nature of their integamient and the great amount of adi- 

 pose tissue which they contain. 



The hibernating habits of the Tachinids which we know to be 

 several-brooded seem to be more variable in character within the 

 species than is the case with the single-brooded forms. With these 

 species there are at the beginning of the period of pupation indi- 

 viduals of the same species in different stages, this being a phenome- 

 non of common occurrence among several-brooded insects in general, 

 of which it is not necessary to explain the causes. Moreover, among a 

 number of individuals of the same species some complete their devel- 

 opment and emerge during the summer, while others undergo a sus- 

 pension of the vital activities in the lar^^al or pupal stage. These 

 forms have as a rule many hosts. Among them may be mentioned 

 Tachina mella, Frontina aletice Riley, and Compsilura concinnata 

 Meig. The first two of the Tachinids mentioned have received consid- 

 erable study as parasites of the tussock moth, and it was noted by 

 Doctor Howard^ that from a number of puparia of the second species 

 mentioned, which were secured during the summer of 1895, the ma- 

 jority of the flies issued from September 19 to October 15 of the same 

 year, but a single specimen issued April 16, 1896. Doctor Howard 

 remarks that, "The usual method of hibernation here must be also 

 in the imago stage although in the case of the fly which issued April 

 16 the puparium must have over- wintered. With these conclusions 

 we fully agree, having observed the same phenomenon to occur in the 

 case of Tachina mella and Exorista amplexa Coq., as parasites of the 

 tussock moths. In Mr. Coquillet's "Revision of the Tachinidge" 

 a number of records are given of the issuance of EupJiorocera clari- 

 pennis from larv^fe collected the preceding season, although it is not 

 clear from the data presented whether the Tachinids passed the 

 winter as puparia or in some of the larval stages. Similar records are 

 given for Winthemia quadripustulata, Sturmid inquinita v. d. W., 

 Frontina frenchii, and several other species. In the cases of this 

 sort which have come under our notice we have found that the para- 

 sites hibernate as undeveloped nymphs within the puparia in the same 

 manner as does Parexorista chelonice. The advantage of this mode 

 of hibernation to the parasite is quite apparent. A number of the 



' 1897. L. 0. Howard. A Study iu Insect Parasitism. Bull. No. 5, Tech. 

 Series, Bur. of Ent. p. 43. 



