218 Annals Entomological Society of America [Vol, VI, 



discovered how the larva reaches the body of the host. The 

 host larva with the three parasites was placed in a tube of sand 

 one inch in diameter together with two other host larvas, one 

 bearing tWo parasites and the other uninfested. The double 

 and triple infested hosts died leaving five parasitic larvas in 

 the tube with the one live host larva. None of the parasites 

 reached the host larva. Host larvae dug from the point where a 

 female fly was seen, to deposit eggs on July 16 had parasites 

 of the first and second instars on the ventral thorax - when 

 removed from their burrows Sept. 23d. About 7 percent of the 

 host larvae are parasitized. While some catches of fifty host 

 larvae were as high as 16 percent infested others were quite free 

 from parasites. This is particularly true in the pine area (see 

 p. 222), where only one out of several hundred host larvae were 

 parasitized. 



The structure of the larva was but little studied on account 

 of lack of material. The head segment bears the usual mandi- 

 bles, which are long and curved. They pierce the integument 

 of the host obliquely; a ring of thickened chitin develgps about 

 them and the mouth is brought into contact with the center 

 of the ring and thus with the tissues and fluids of the body 

 (Fig. 8). The number of larval moults has not been fully 

 determined and the following account is not necessarily ac- 

 curate. The smallest larvae found are from 0.5 to 0.6 mm. 

 in length and are evidently in the first instar. These were taken 

 in late summer and autumn and occasionally in spring. Most 

 of these larvas moult in the fall; all pass the winter attached 

 to the body of the host, those of the first stage moulting in early 

 May. When the larva moults, the integument splits in the 

 region of the thorax. The anterior end of the body is withdrawn 

 from the old skeletal parts, leaving the old mandibular skeleton 

 imbedded in the host. The posterior part of the larva apparently 

 remains in the old integument until the new integument of the 

 head region is hardened when a new attachment to the host 

 is affected. When again attached, the larva withdraws the 

 abdomen from the exuvium (Figs. 5, 6 and 7). 



The larvas of the second instar, (length 1.2 to 1.6 mm.), 

 probably moult again after the host has fed about a month 

 (early June) , but this is not certain because exact measurements 

 could not be made of the small living larv® while attached to 

 the host and they could not be removed without killing them. 



