BLACK GRAIN-STEM SAWFLY. 9 



clypeus, and articulations of mandibles brownish. Thoracic legs small, papilli- 

 form, and pale brownish. Dorsal abdominal segments triannulate; pleura 

 prominent; ventral segments triannulate; prolegs absent. (For further de- 

 scription see Plate I, A, and key to larvae.) 



Larvae of this species are apt to be confused with those of Cephus 

 pygmaeus and C. ductus. All three species infest the small grain 

 crops in practically the same manner, have very similar biologies, 

 and superficially resemble one another closely. The following key in 

 conjunction with the accompanying figures will, it is believed, make 

 it possible to recognize them: 



KEY FOB SEPARATING GBAIN-INFESTING SAWFLY LABVffi. 



1. Dorsal anal lobe of the tenth tergite viewed from the side triangular, slop- 



ing gradually from base to apex, the anterior end of lobe much thicker 

 than the. posterior end which is more or less acute. Spines on the anal 

 prong each arising from a small, more or less chitinized tubercule and 

 closely grouped about the apex of the enlarged fleshy portion just 

 basad of the short chitinized apical ring. Eighth and ninth tergites ap- 

 parently glabrous 2. 



Dorsal and lobe viewed from the side not triangular, not sloping gradu- 

 ally from base to apex but convexly rounded, the posterior end of the 

 lobe as thick dorso-ventrally as the anterior end and nearly perpendicu- 

 lar. Anal prong completely encircled by two irregular series of widely 

 separated, short, stiff spines which do not arise from chitinized tubercules. 

 Eighth and ninth tergites each with a transverse row of distinct short 

 hairs. (See Plate I, A.) Trachelus tabidus Fab. 



2. Anal prong terminating in a short chitinized ring which is not as long as 



broad. Spines basad of chitinized ring few in number, confined to a single 

 transverse row on the dorsal surface. Dorsal, lateral, and ventral lobes 



all sparsely hairy. (See PI. I, A.) Cephus pygmaeus Linn. 



Anal prong terminating in a chitinized tube-like process which is distinctly 

 longer than broad. Spines basad of the apical tube-like process numerous, 

 arranged in two irregular contiguous series completely encircling base of 



tube. Anal lobes all more distinctly hairy. (See PI. I, A.) 



Cephus ductus Nort. 



MANNER OF WORK AND PROBABLE LIFE HISTORY. 



Observations by the writer supplemented by those of McConnell 

 and Myers, and confirmed in part by Kulagin (47) indicate that 

 the life history of Trachelus tabidus does not differ greatly from that 

 of the western grass-stem sawfly, Cephus cinctus. The early stages 

 have not yet been observed in this country. Collections of adults 

 in the field indicate that egg-laying takes place during the period 

 May 15 to June 10. Some of the emergence records for reared 

 specimens show somewhat earlier dates than May 15, but since 

 these were obtained under the abnormal conditions of the labora- 

 tory they may be disregarded. Kulagin indicates about the same 

 period for egg-laying in Russia. 

 148465°— 20— Bull. 834 2 



