20 THE REPORT OF THE No. 36 



might be termed a normal ratio it must have wiped the wheat crop out of 

 existence. We have noted similar conditions in Manitoba more than once, which 

 have led us to suspect that meteorological factors play an important part in the 

 development of the sawfly. This has been still further borne out by a survey of 

 the province and by an examination of the reports issued by the Manitoba and 

 Saskatchewan governments, together with those of the Manitoba Free Press. We 

 found in these surveys that the greatest prevalence of Cephas followed very 

 closely the areas of least rainfall, and that Avhere the moisture was ample 

 the injury fell to a marked degree. This fluctuation, apparently due to humid- 

 ity, was even well marked over local areas. It was also apparent that the low, 

 moist, portions of a field were much less infested than the high drier parts. 

 More data is necessary before definite conclusions can be arrived at but judging 

 from our experiments, rain in itself is not harmful except during the adults' 

 life. It would seem, therefore, that the cause of the greater immunity lies in 

 the quicker growth., this in its turn perhaps providing an excess of sap that is 

 detrimental to the sawfly larvae. In any case the facts of this flutuation are 

 hopeful because they indicate that with the passing of dry seasons the sawfly 

 menace may become less acute. 



Remedies. The remedies for the Western Wheat-stem* sawfly are entirely 

 cultural, and the most important of them consists of ploughing down the in- 

 fested stubble any time between August 1st and June 5th of the following year. In 

 order to be thoroughly effective the ploughing must be well turned so that there is 

 no overlapping edge to the furroAvs, and it should be not less than six inches 

 deep. A wide furrowed plough is better than a narrow one for this purpose. 

 Fall ploughing will pack during the winter, but that done in the spring should 

 be packed by machinery. 



In addition to the destruction of larvae by ploughing a good deal can be 

 accomplished by sowing immune, or partly immune, crops. Oats, for instance, 

 are perfectly free from attack ; barley, owing to its rapid growth escapes, with 

 small injury, while winter rye is able to withstand the insects' effort to a marked 

 degree and, on account of its early ripening, is cut before loss occurs. Indeed, 

 there are indications for the belief that winter rye may prove one of the most 

 important checks to tihe development of the sawfly owing to the fact that it 

 is often heavily infested but 'the sawfly larva? are usually unable to mature in 

 it. Moreover, even should they develop normally, the early ripening of the rye 

 enables it to be harvested before the larva? can get below the point where the 

 straw is cut by the binder and as a result they perish. 



Trap Crops. We have noted that volunteer wheat on land intended for 

 su man erf allow is often a great attraction for adult sawflies that have emerged in 

 the vicinity. On one such plant we counted 14 of these insects at rest, while on 

 another three were attempting to oviposit at the same time. It is probable, 

 therefore, that a single plant of this nature might be the receptacle for many 

 eggs, especially as it is not uncommon to find the remains of two or more larva? 

 in one stem. For this reason we believe that a narrow strip of thinly sown wheat 

 round the edges and across the middle of a field intended for summerfallow, might 

 attract and be the means of destroying a large number of these insects. 



Crop Rotation. Should the sawfly continue to maintain its present pro- 

 portions or increase still further, then it will he necessary to consider more 

 drastic measures of control and make an initial sacrifice in order to reduce the 

 pest sufficiently to make wheat growing profitable. To do this farmers in in- 



