26 BULLETIN 841, U. S. DEPARTMENT OE AGRICULTURE. 



procedure leaves all the infested stems of wheat on the surface, and 

 nothing could be more favorable for the escape of the adult flies in the 

 following spring. The wheat stubble seems to be necessary to hold 

 the winter snow for the protection of the young rye, hence the farmers 

 seldom or never plow the stubble under before sowing the rye. 



Previous to the year 1919 it had been stated with much confidence 

 by men who were known to be good observers that durum wheat 

 was nearly immune from the attacks of the sawfly. On the strength 

 of these statements county agents were inclined to recommend a modi- 

 fication of ordinary farm practice, at least to the extent of barring 

 from that region Fife and Marquis and the softer-stemmed wheats 

 in the hope that by this means the work of the sawfly might be 

 checked and a more certain harvest assured. It was readily seen 

 that an immune wheat would solve the problem of the sawfly. 



Observations made by the writer during the month of August, 

 1919, and recorded on an earlier page of this paper, included in their 

 scope an inquiry into this question concerning the immunity of 

 durum wheat. Farm work was too far along at the date of this 

 visit to permit of effective field work to settle the matter definitely, 

 but several farmers informed the writer that durum had suffered 

 severely that year, although not as much as either Fife or Marquis. 

 These reports must be accepted at their face value since the agree- 

 ment on this point was general. 



The immunity of durum may vary from year to year and is 

 possibly based on the relative dates of the appearance of the adult 

 Cephus and the rapidity of growth of the young grain. The stem 

 of the durum wheat is more dense and unyielding than that of other 

 wheats, and if a warm rainy spring should hasten its growth it might 

 prevent the sawfly from placing many eggs. A number of unknown 

 factors enter into this problem that hinder its complete solution 

 at the present time. 



CEPHAS PYGMAEUS L. 



In certain parts of the country the occurrence of Cephus ductus 

 appears to have. been confused with that of its congener Cephus pyg- 

 maeus, a sawfly stem-borer that was probably imported from Europe 

 only a few years previous to the first mention of Cephus ductus in the 

 United States. The habits ,of the two species are so similar that a 

 brief synopsis of the life history of Cephus pygmaeus is given herewith 

 together with a condensed description of the same insect. 



As far as is now known the imported species does not yet occur 

 west of the Mississippi River, while the western grass-stem sawfly 

 has been found for the most part only west of the same river. 



C. pygmaeus was first observed in 1887 in the vicinity of Ithaca, 

 N. Y., and in 1889 Prof. J. H. Comstock published l an account of its 



