REPGRT OF THE E^'TOMOLOGIST A.ND BOTANIST M 



SESSIONAL PAPER No. 16 



August, -which will attract the females to lay their eggs; these strips must afterwards 

 be i>loughed down before the larvis are mature when they will be killed, and the 

 wheat which is sown late will escape owing to the egg laying females having all 

 deposited their eggs. This end may also be obtained by running a harrow over the 

 stubble as soon as the crop of fall wheat is cut so as to start a volunteer crop from the 

 grain which had been shelled out in harvesting. This volunteer crop wnll form an 

 attraction to the females before the main crop appears above the ground and can be 

 ploughed down deeply at any time before the larvse mature. 



Heports of injuries by Hessian Fly from Manitoba proved upon investigation to 

 be unfounded. 



Wheat-stem Sawfly, Cephus occidentaiis, Riley & Marlatt. — This insect which 

 has been referred to occasionally in previous reports of the Division, last autumn 

 appeared in central Manitoba and the eastern part of Saskatchewan, in much more 

 serious numbers than at any previous time. The broken down straws which resulted 

 from its attacks were seen in many fields and caused some alarm. Among corre- 

 sjponclents who reported on this insect, Mr. Norman Griddle, an observant farmer and 

 stud 'lit of insects, living at Aweme, Manitoba, writes at the end of the season as 

 follows : — 



' This native species of sawfly which until the breaking up and cultivation of the 

 prairies was confined to a few native grasses belonging to the genus Agropyrum, of 

 which A. caninum, R. & S. here is the favourite, has increased considerably during the 

 last year or two. In the absence of parasites this insect seems to have been controlled 

 by the number of flowering stems formed by its food plant, the grass in its turn being 

 restricted by the climatic conditions of the season, so that an unfavourable season for 

 the grass to form flowering stems would also prove unfavourable to the increase of 

 the sawfly; but with the cultivation of the prairie and the planting of cereals the 

 conditions change. For, although native grasses seem still to be preferred, yet if 

 on account of the season, as is sometimes the case, they fail to develop stems abun- 

 dantly or the insects are too numerous for the stems of the grasses produced, the flies 

 turn their attention to wheat or rye, as well as to the western rye grass, Agropyrum 

 icnerum, Vasey, which is now so extensively grown in Manitoba, causing serious 

 damage to that important crop. These conditions occurred in 1907 with the results 

 that in some cases fully 50 per cent of the wheat stems .were broken down around 

 the edges of fields, extending in to a distance of 100 feet or more, and damage was 

 apparent to a lesser extent all through the crop. An interesting feature in connection 

 with this attack upon wheat, was that fully 75 per cent of the infested stems were 

 broken down by wind about 2 or 3 inches above the ground, close to where the larvsa 

 were at work; and in many instances an examination showed that the larvse had been 

 caught by the breaking of the straw, some actually at the broken spot, when they 

 were pinched to death, while in others they were above the break, which proved equally 

 fatal to them. I calculated that on a certain area fully 12 per cent were killed in this 

 manner. It is interesting to note that the native grasses, however, never break in 

 this way, so that in attacking wheat the insect has to contend with conditions which, 

 though favourable to its increase, are not so much so as an abundance of its native 

 food plant would be. The life history, so far as I know it, seems to be about as 

 follows: — The eggs are laid singly upon a stem of grass or wheat, not far from the 

 head, between June 20 and the second week of July. The larvte soon hatch and begin 

 to eat down inside the stem, usually reaching maturity and the ground towards the 

 end of August. They then eat the stems almost through, slightly below the ground, 

 so that they lyreak off. The stubs are then closed over with a water-tight material 

 and the insides of the stems are also lined by the larvjc to the roots. In these retreats 

 the Ir.rvaj pass the winter and remain in an active condition unchanged until May of 

 the following year, when they turn to pupss and emerge as perfect sawflies towards the 

 end of June, the date varying somewhat with the season.' 



