70 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



The structure and general appearance of the larva are shown in 

 figure 36. The larva is legless, subcylindrical, white in color except 

 the heavily chitinized and therefore reddish-brown headcapsula. The 

 full grown larva is about 3.7 mm. long. Three thoracic and nine 

 abdominal segments are well developed. The anal lobes may be re- 

 garded as a tenth abdominal segment. The three thoracic segments 

 are nearly equal in size and only little larger than the first abdominal 

 segment. The abdominal segments decrease slightly in width and 

 length toward the apex. All segments and the head are armed with 

 constant setae. The statement of Hopkins (38) that " with the ex- 

 ception of scattering hairs on the head and on the scutellar lobes of 

 the thoracic and abdominal segments the body is without distinguish- 

 ing vestiture " in Dcndroctonus has been found to be not true. There 

 occur at least in Dendroctonus valens distinct setae. That this is not 

 exceptional in the Scolytidae has been proved by Russo (57) and the 

 author. The latter has studied many species and has found that every 

 examined species shows distinct setae. The following discussion is 

 based on the full grown larvae only. The fact that the present study 

 was made in a private home did not allow of rearing work and there- 

 fore the question of molds, etc., cannot be discussed at present. 



THE CHITINOUS SKELETON 

 THE HEAD 



The head of the larva is more simple in structural details than 

 that of the adult. It is distinctly narrower than the first thoracic seg- 

 ment when seen from above, but nearly equal in length and in width 

 to the latter when viewed from the side. The general structure is 

 shown in figure 36, the anatomical details in figure 37. The more 

 striking differences in the larval head are found in the presence of 

 a clearly defined front, clypeus, labrum, and a well developed sub- 

 mentum. 



Epicranial suture. — The sutura metopica as well as the sutura 

 fronto-verticale are well developed and double lined (a, b). They are 

 not raised or padded as in the adults. 



Front. — The front (fig. 37, Fr) is triangular in outline, plano-con- 

 vex and clearly defined by the epicranial suture. The lateral sides are 

 bordered with six strong bristles each (d). These setae are here 

 called setae fronto-lateralis. The base of the front is smooth without 

 any armation. 



In the discussion of the larval setae it seems to be very useful to 

 compare the results obtained with those of other authors. From the 



i 



