THE WESTERN GRASS-STEM SAWFLY. 27 



life history as worked out by himself. From this bulletin the follow- 

 ing summary of its habits and appearance has been compiled. 



The adults, in the latitude of Ithaca, appear during the month of 

 May and at once begin oviposition in the stems of wheat, just as the 

 grain is jointing. In the majority of instances the eggs are placed 

 above the third joint, and the larval gallery extends from the point 

 of oviposition, or a little above, to the extreme base of the plant. By 

 the time the wheat is ready to cut, early in July, a large majority of 

 the larvae have descended to a position below the level of the reaper 

 cut and are safe from removal with the harvested straw. A week 

 later nearly all the larvae have girdled the stems within and part have 

 already spun the silken lining of the hibernation chamber. 



Cephus pygmaeus is a well-known species in Europe and has been 

 described by both English and Continental writers. In France it 

 has been considered a very serious pest and is said to attack both 

 wheat and rye. 



DESCRIPTION 



Adult shining black, banded and spotted with yellow. Length of male 8 mm., of 

 female 10 mm. Head large with prominent eyes ; three ocelli near summit. Antennae 

 inserted on front nearly opposite middle of compound eyes, and composed of 19 or 20 

 segments. Wings transparent, iridescent, somewhat smoky, with costal margin yel- 

 low toward base. Mouth-parts (except tips of mandibles),. a spot on clypeus, a nar- 

 row margin between compound eyes and mouth-parts, ventral aspect of thorax, legs 

 (except a dark band on coxse and femora), membrane at base of abdomen, caudal 

 margin of each abdominal segment ventrally, a more or less well-marked spot on each 

 side of first and second abdominal segments, a broad band occupying caudal three- 

 fourths of third and fifth segments, a narrow band on caudal margin of sixth segment 

 often more or less interrupted forming spots on back and sides, and latero-caudal 

 angles of seventh segment, yellow in male. 



In female, spots and bands usually smaller and sometimes entirely wanting ven- 

 trally. 



Both this species and Cephas ductus vary greatly in their mark- 

 ings. Mr. S. A. Rohwer, of the Bureau of Entomology, who has given 

 much critical study to this genus and has examined a large series of 

 individuals, mostly reared from known host plants, states in a recent 

 publication: 2 "The introduced, European, Cephus pygmaeus (Lin- 

 naeus) is very similar to the native species common throughout the 

 west and it is difficult to find characters which distinguish the two in 

 all their forms." 



1 Comstock, J. H. A saw-fly borer in wheat. In Bul.ll, Agr. Exp. Sta. Cornell Univ., Nov., 1889. 



2 Rohwer, S. A. The American species of the genus Cephus Latreille. In Proc. Ent. Soc. Wash., v. 19, 

 p. 139-141. 1917. 



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