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By C. N. AINSLIE,' Entomological Assistant, Cereal and Forage Insect Investigations

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The western grass-stem sawfly (Cephus cinctus Norton) (fig. 1) is in many ways one of the most interesting and important insects that has attracted the especial attention of economic entomologists in recent years. It is a species native to the United States and has been gradually coming into prominence since the beginning of the present century by reason of the change which the feeding habits of the larvæ have been undergoing subsequent to its discovery. Originally a grass feeder, it is becoming a serious menace to the grain growers of the Northwestern States because of its acquired appetite for small grains, within the stems of which it now subsists.

Such changes of diet are probably occurring everywhere with greater frequency than formerly was deemed possible, especially among the phytophagous insects of the Middle West. When given a

1 The writer wishes to express his appreciation of the assistance afforded by Messrs. J.C. Crawford, A. B. Gahan, and S. A. Rohwer, of the Bureau of Entomology, in the preparation of this paper, the two former in determining parasitic material reared during the progress of the studies of the saw fly, the latter in making a critical examination of a large scries of sawlly individuals reared or collected from various parts of North America, and for furnishing detailed descriptions of Cephus cinctus besides a key to the North American species of the genus Cephus. Helpful criticisms from these men have added to the value and accuracy of the paper.

The writer desires also to mention the valuable assistance and cordial cooperation of Mr. Norman Criddle, entomological field officer for Manitoba, Canada; of Mr. A. P. Henderson, of Bottineau, N. Dak., and of the several county agents in the insested areas, who have aided in various ways in the accumulation of information and material.

150056-21_Bull. 841-1

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