April, '11] CRIDDLE: MANITOBA INSECTS OF 1910 237 



are responsible for most of the injury to young wheat that 

 is noticeable almost every spring and put down to other causes, such 

 as Hessian fly, wire worms, rot, etc. The attack is recognizable by .a 

 patchy appearance of the growing grain; odd plants, or more often 

 several in succession may be seen to have wilted away. Examination 

 will show that plants look as if they had been pinched about an inch 

 below the ground, or to have rotted at that point; while a careful 

 search usually reveals one or more whitish or greenish maggots which 

 are very small at that time. About a month later, as wheat shows 

 signs of heading out, there is another generation which causes the 

 well known "White heads." 



During the present year injury to young wheat was not as extensive 

 as in 1909, though probably at least 1 per cent of young plants were 

 killed. In July adults of M. americana could be swept up in fair 

 nunibers from grain fields and many stems of wheat were infested 

 with larvae. I note that this insect seems to be very partial to couch 

 grass — Agropyron repens and A. occidentale. On a patch of the latter 

 flies were collected weekly from May 6 until September 21. 



Western Wheat-Stem Sawfly, Cephus occidentalis. — This is an in- 

 sect that usually confines itself to native grasses upon which it sub- 

 sisted entirely before the introduction of grain; its food plants being 

 species of the genus Agropijron — especiall}'^ A. caninum. Happily A. 

 tenerum, which is now so extensively grown in western Canada, has 

 proved almost immune, due, no doubt, to its more slender stems. 

 This sawfly, however, readily adapts itself to new conditions and 

 having once become established, seems to have a preference for the 

 plants that it fed upon in its early stages. In 1906 owing to a failure 

 of its native food plant to produce heads, it swarmed to the wheat 

 fields, where it soon became established and, in some cases, where 

 proper precautions were not taken, remained ever since. As there 

 are still some details lacking in the published accounts of its habits, 

 it may not be out of place to give a more detailed account of its life 

 history. 



The flies appear on an average about June 15, when they can be 

 observed, resting head downwards, upon stems of grain and grasses. 

 They deposit their eggs towards the end of the month at the time 

 wheat is showing indications of — or is — heading out. The operation 

 has not been observed, but doubtless the eggs are laid singly in the 

 stem near the head by aid of the short ovipositor. The egg hatches 

 within a few days and the larva commences to work its way downwards 

 by eating out the inner tissues, and reaches the ground about the first 

 of August. It then gnaws a ring around inside, causing the stem to 

 fall down, then makes a chamber of the stub by covering the surface 



