lug. 28, 1916 



Thersilochus Conotracheli 



853 



FlG. 4. — Thersilochus conotracheli: Ven- 

 tral surface of head of first larval instar: 

 a, Labrum; b, maxilla; c, labium; d, 

 mandible. Highly magnified. 



parently they are attached very close together at a point above the 

 labium. During its first instar the larva undergoes a comparatively 

 enormous increase in size, becoming ultimately 2 mm. in length and 

 much distended, only the head and taillike 

 appendage retaining their original dimen- 

 sions. The approximate appearance of the 

 parasite at this period of its development is 

 shown in figure 5. 



Second instar. — With its first molt the 

 larva acquires an entirely different appear- 

 ance. The first larval skin splits longitudi- 

 nally just back of the head and the forward 

 part of the body is drawn out. Then the 

 skin is pushed off from the caudal end of 

 the body. The head shield remains intact. 

 The larva that emerges lacks the taillike 

 appendage and the prominent, heavily 

 chitinized head. Its mouth parts are ap- 

 parently entirely soft, and the most careful 

 preparation and mounting of specimens has 

 failed to disclose any mandibles. The mouth has the appearance of a 

 dimplelike depression without armature. At full growth this instar 

 (fig. 6) is about 3 mm. long. The head measures 0.31 mm. broad. 



Third instar. — 

 The third instar is 

 very like the second, 

 except that it is 

 larger, slightly 

 stouter, and the 

 head is 0.38 mm. 

 infallible distinction 

 between the two stages. At full growth the third instar is about 3.50 

 mm. long. 



Fourth instar. — With the assumption of the fourth instar the larva 

 acquires the typical ichneumonoid larval characteristics. It is now in 

 the form of a curved spindle, thick 

 in the middle and tapering toward 

 each end. It is about 4 mm. long 

 with the head nearly a half milli- 

 meter broad, and with fairly dis- 

 tinct mouth parts. With high 

 magnification the lab rum, mandi- 

 bles, maxillae, and labium can be dis- 

 tinguished as well as the maxillary and labial palpi. The palpi appear 

 merely as low rounded elevations on the surface of the maxillae and 

 labium. The mandibles are cone-shaped, and somewhat drawn out to 



Fig. 5. — Thersilochus conotracheli: Full grown larva of the first instar. 

 Highly magnified. 



broad. This measurement constitutes the only 



Fig. 6.- 



Thcrsilochus conotracheli: Larva of second 

 instar. Greatly enlarged. 



