136 PROC. ENT. SOC. WASH., VOL. 23, NO. 6, JUNE, 1921 



tel; the terminal sclerites of the body of the adult female are simple and un- 

 specialized. 



BIOLOGY. 



The oviposition of this species has not been observed; but the 

 structure of the reproductive system and of the primary larva 

 indicates that the larvae are deposited directly on the body of 

 the Pyrausta caterpillar during the period when the latter is 

 feeding on the exterior of the plant or moving from place to 

 place. 



Immediately or at all events very shortly after entering the 

 body of the host caterpillar, the primary larva enters one of the 

 longitudinal bands of adipose tissue. The larvae of the autumn 

 generation remain in the fat body during the winter (Fig. 20), 

 which they pass in the second larval stage; during the initial 

 period of its existence the larva has no connection with the 

 tracheal system of the caterpillar and it must therefore obtain 

 its supply of oxygen either from the ingested blood and adipose 

 tissue of its host or from the fine tracheae which penetrate the 

 fat body in which it lies; later on, however, the second stage 

 larva applies its posterior extremity to a trachea of the cater- 

 pillar and forces an opening through which it secures a more 

 abundant supply of oxygen; sometimes the larva attaches itself 

 to one of the larger tracheal vessels, but more often to the finer 

 branches which supply the fat body; in this stage it is thus sur- 

 rounded by a sheath of mixed tracheal and fatty origin, in which, 

 however, the adipose elements greatly predominate. Finally, 

 after the second ecdysis, the parasite larva, which up to this time 

 has fed only upon the blood and adipose tissue, begins to devour 

 indiscriminately all of the internal organs of the caterpillar of 

 which it leaves little but the skin. 



The parasite larvae of the winter generation which we have 

 had under observation have invariably emerged from cater- 

 pillars of the borer and this is also the usual habit of the larvae 

 of the summer generation; but in one case a larva of the summer 

 generation was observed to emerge from a chrysalid of the 

 borer. 



The larvae pupate in the gallery of the host beside the empty 

 skin of the caterpillar from which they have emerged. 



It is not necessary to consider in detail in this paper the 

 changes produced in the structure of the adipose tissue of the 

 host by the presence of the parasite larva; it may be noted, 

 however, that the zone of adipose tissue immediately adjacent to 

 the body of the Tachinid larva eventually takes on a light 

 yellowish tinge, contrasting with the pure white color of the nor- 

 mal tissue in this species; in older larvae, the part of the adipose 

 tissue forming the sheath becomes semitransparent owing to the 

 disappearance of the fat globules from the cells composing it. 



