14 ILLINOIS BIOLOGICAL MONOGRAPHS ^332 



II. MORPHOLOGY 



The external anatomy of the larvae of the Tenthredinoidea has received 

 but little attention from entomologists. The only important contribution 

 on the subject is MacGillivray's study (1913), which deals with the anat- 

 omy and coloration as well as with the biology of the larvae. The writer 

 has made a comparative study of the external anatomy of the larvae of 

 representative Nearctic Tenthredinoidea in order to find characters upon 

 which both analytic and synoptic classifications of the larvae might be 

 based. Since MacGillivray has treated the general aspect of the anatomy, 

 only the more important structures and features will be discussed in the 

 following pages. 



The larvae of the Tenthredinoidea (Figs. 1-25) are typically subcylin- 

 drical, cruciform, caterpillar-like, slightly flattened on the ventral aspect, 

 and usually taper slightly caudad. In the leaf-miners the body is de- 

 pressed. The body in its metamerism is well differentiated into a head 

 and a series of thirteen somites which are more or less similar in structure. 

 The segmentation is distinct. The first three segments compose the 

 thorax and are distinguishable on account of their position, form, and, 

 in podous larvae, more readily by the presence of three pairs of thoracic 

 legs. The abdomen consists of the ten remaining visible segments and in 

 polypodous larvae the presence of larvapods gives a characteristic appear- 

 ance to the uromeres. They are usually subdivided by transverse depres- 

 sions into annulets. 



Head. — The head (Figs. 26-38) is typically subglobose, more or less 

 circular in frontal contour, strongly chitinized, and usually setiferous. 

 The mouth is directed ventrad or slightly ventro-caudad. In the leaf-min- 

 ers it is directed cephalo-ventrad as in the Fenusinae (Fig. 34) or cephalad 

 as in Phlebatrophia (Fig. 37). The surface of the head may be polished 

 and shiny as in Neodiprion (Fig. 28), or roughened, verrucose, or granu- 

 late, and divided into minute irregular areas as in Pteronidea (Fig. 30) 

 and the Cimbicinae (Fig. 29), or, in life, thinly coated with a waxy secretion, 

 as in some Emphytinae. It may be glabrous as in Metallus (Fig. 35) and 

 Phlebatrophia (Fig. 37), or it may be variously setiferous as follows: 

 microscopically and sparsely setiferous as in Tremex; with a few scattering 

 setae as in the Phyllotominae; with minute stiff peg-like setae as in Neodi- 

 prion; with numerous promiscuously distributed short setae as in Dolerus 



