172 



EXPERIMENTAL FARMS 



3-4 EDWARD VII., A. 1904 



Wheat-stem Sawfly (CepTius vygmoeus, L.). — An insect which appears in a rather 

 intermittent manner in Manitoba and the North-west Teritorriea is the Wheat-stem 



•• Sawfly. Although present in considerable numbers in a locality 



one year, it seldom appears again in the same place the follow- 

 ing year. It has from time to time been reported from Central 

 Manitoba right across the plains to the Kocky Mountains. 

 There are, I believe, other species of Cephus which attack various 

 grasses in the West. In 1902, Mr. Norman Criddle sent me from 

 Aweme, Man., a large number of stems of two grasses, Ammo- 

 pliila longifolia and Agropyrum caninum, which were attacked 

 by Cyphid larvae. Judging from the colour — one was bright yel- 

 low and the other white like the Wheat-stem Sawfly — there were 

 at any rate two species ; but, unfortunately, I failed to,' rear any 

 of the flies from the large amount of material sent me by Mr. 

 Criddle. During the past season I received several infested 

 v/heat straws from Mr. John Davis, of Waskada, Man., who 

 wrote : — 



Fig. 3. — "Wheat-stem 

 Sawfly : a, cocoon, 

 6, boiiugs. 



August 19. — I am sending you a few stems of wheat 

 which I and many otliers here would like you to report upon. 

 You will notice that some of the straws are broken or bent down 

 three or four inches from the ground. The cavity of 

 the straw is full of fine dust, and there is a small white 

 grub about half an inch in length. This I have generally found low down quite 

 near the root. It is very general through this district, but is not very destructive. 

 The straws fall as they get dry, and where the attack is slight it might easily pass 

 unnoticed. I have one field of 45 acres summer-fallowed last year. We were estim- 

 mating this to yield 30 bushels to the acre. There is about 5 per cent of this field 

 down. I have not seen any other field so badly attacked as this is, but I have not seen 

 any field about here that is quite clear of injury. It is a new pest here, and no one 

 seems to know anything about it.' 



This insect has provisionally been named Cephus pygmceus, L., and it certainly 

 bears a close resemblance to that European species; but there are some points in its 

 habits and life-history which do not agree, and it is just possible that the insect which 

 occurs in our North-west may be a native grass-feeding species which occasionally 

 attacks wheat when it finds that plant in a suitable condition at the time the females 

 are laying tlieir eggs. This can only be proved by carefully rearing a large series of 

 the insects. The perfect insect is a shining black four-winged sawfly, banded and 

 spotted with yellow, and having the abdomen slightly compressed. The head is large, 

 with prominent eyes, the antennje slightly club-shaped and composed of about 20 seg- 

 ments. The female is rather larger than the male and less ornamented with yellow. 

 The average length of this fly is about one-third of an inch. The eggs are laid pro- 

 bably about the 1st of July, just before the wheat comes into head. They are inserted 

 into the hollow of the stem by means of the female's saw-like ovipositor. The egg 

 hatches in a few days, and the larva grows rapidly ; before the straw ripens and hardens 

 it will have eaten its way from the topmost joint of the stem to the lowest, feeding on 

 the substance of the knots and on the inside tissues of tlie straw. About the time the 

 grain ripens, it goes down to the lowest joint and gnaws away the inside of the straw 

 so as to cut a ring almost, but not quite, through to the outside. This is just above 

 or at the surface of the ground. The larva then burrows further down into the base of 

 the stem and spins a very fragile skin-like cocoon, in which it remains unchanged until 

 the following spring. The date of appearance of the perfect insect varies witli the sea- 

 son and locality. I have taken specimens by sweeping, both in grain fields and on- the 

 prairie, from the last week of June to the middle of July. As all the larvae pass the 

 winter in the base of the straw, remedial measures must aim at treating the stubble 



