OF WASHINGTON, VOLUME XIX, 1917 139 



THE AMERICAN SPECIES OF THE GENUS CEPHUS LATREILLE. 



BY S. A. Rniiu KR, 

 Forest ///.*<r/.s-. Jlm-in// of K iiiiniinlni/i/. Washington, D. C. 



This paper, which is a contribution from the Branch of Forest 

 Insects, Bureau of Entomology, is the result of a careful study of 

 a large series of specimens of Ceph us reared from the stems of 

 various grass-like plants and is an attempt to separate the species 

 which are injurious to American Cereal and Forage crops. For a 

 number of years the writer had been of the opinion that there 

 were a number of distinct forms responsible for the damage done 

 to cereal and forage crops in the west, but a critical examination 

 of a large series from the same locality and host has proven that 

 the forms previously distinguished are only extreme variants of 

 the same species and that there are all the necessary intermediates 

 to show that there is only one species involved. 



The introduced, European, Cephus put/indent (Linnaeus) is 

 very similar to the native species common throughout the wesl 

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

 all their forms. The characters offered in the following key are, 

 however, reliable for the material available. 



KEY TO THE NORTH AMERICAN SPECIES OF CEPHUS. 



Stigma and costa dark brown of a uniform color; mesepisternum Muck; 

 femora black; apical tergite and venter Mack; face and scutellum black 

 (face of male with yellow spots). ........ pi/gmacus Linnaeus 



Stigma in greater part and costa yellow; mesepisternum with the upper 

 angle yellow; apical tergite and usually the venter in part yellou ; 

 femora usually mostly yellow; face and scutellum of female usually 

 black but occasionally with yellow spots ............ cinctus Norton 



Cephus cinctus Norton. 



Cephus rinrtiix Norton, Tran. Amer. Knt . Soc., vol. 4, 1876, p. 86. 

 Cephus occidfiilnli* Kilcy and Marlatt. Insect Life. vol. 4, 1891, p. 177. 

 Cephus graenichen Ashmead, Can. Ent., vol. 30, 1898, p. 182. 



The above listed synonymy was first pointed out by Konow 

 in his Chalastogastra, p. 2t>5 (published in Zeit. Hym. Dipt.. 

 1905, p. 249). The species cinctus is subject to considerable 

 variation in color and structure. The variation in structure 

 consists of the variation in the relative lengths of the postocellar 

 line as compared with the ocellocular line. The postocellar 

 line varies from distinctly shorter (as high as a ratio of 5 to 7) 

 than the ocellocular line, to subequal with it, to longer (as high as 

 a ratio of 7 to 5.5) than the ocellocular line. In a series of t wenty- 



