REPORT OF TEE ENTOMOLOGIST AND BOTANIST 165 



SESSIONAL PAPER No. 16 



more or less noticeable depression in the soft stem inside which they lie. When only 

 one or two maggots occur on a straw the injury is not very severe and attacked stems 

 when not knocked down by high wind at harvest time may produce fairly heavy grain. 

 Sometimes, however, the maggots suck the sap to such an extent that the stem is killed 

 at the point of injury and the tissues separate, when the stem falls over, displacing the 

 flax-seeds and making them appear as if they had formed inside the stem. This was the 

 case last season in Manitoba and caused uncertainty on the part of some observant far- 

 mers as to the identity of the insect which had done the injury. I am obliged to my 

 correspondent, Mr. Sanford Manson, for calling my attention to this matter; for it 

 should certainly be mentioned when describing the nature of the attack of the Hessian 

 Fly. He writes : — 



' Nov. 23, Sperling, Man. — I send a few wheat stems that have suffered from insect 

 attack this summer. I have just received a very welcome bulletin (No. 52) which 

 treats of insects; but I cannot find anything which resembles it nearer than the Hes- 

 sian Fly ; only the description of that insect states that it is found on the outside of the 

 stem beneath the sheath of the leaf. You will notice that this pupa is inside the stem. 

 I spoke to a number of farmers about the matter, and they all agreed that the pupa 

 was inside the stem. It did not seem to affect the wheat very much, as the broken down 

 heads were as well filled as the standing ones; but in some fields the loss from breaking 

 down so low was that the binders could not pick it up. This made considerable loss, 

 variously estimated at from two to five bushels per acre. It seems to have been general 

 in this diistrict. About the last of September it was found that the pupa had developed 

 and the grvib had eaten its way out. Therefore, it is only the deserted shell, which I 

 am sending jow. Both early and late sown wheat suffered.' 



The material sent showed that some of the flax-seeds were as stated inside the 

 straw; but in these cases the injured straw was blackened from decay, and shreaded 

 and broken up by the twisting of the straw at the time it bent and fell over. By 

 Roftening the stems in water and examining them carefully, the cavity in which the 

 larvae had lain while active could always be traced; and, although this depression was 

 deeply dented into the stem, it was actually on the outside of it, beneath the base of 

 the leaf sheath. Mr. Manson and some other correspondents have referred to empty 

 flax-seeds being found on the stems in autumn. This is an important matter as it in- 

 dicates the pTobability that parasites or other natural enemies have been at work, and 

 H is therefore a very hopeful sign for the future. 



There are several! parasites which prey upon the Hessian Fly, and their good 

 offices in the past have been the chief cause of the sudden disappearance from infested 

 districts of this serious enemy of the farmer. When emerging naturally, the pupa of 

 the Hessian Fly works its way out of the brown flax-seed-like puparium and the gauzy, 

 empty, pupa-case is left, protruding conspicuously from the end. A parasite on leaving 

 the puparium gnaws a ragged hole which may be in any part of the puparium. In 

 Manitoba there is only one brood of the Hessian Fly. The puparia are foiind in the 

 late summer. By harvest time all the larvae have turned to the flax-seed stage, and 

 the flies do not emerge until the following June. A knowledge of the habits of the 

 insect in Manitoba suggests the best remedial measures. The puparia of all the mag- 

 gots which attack the root shoots in early summer, and most of those on the straw 

 are left in the stubble fields after the wheat is cut. An effective way of disposing of 

 these is, when it is conveniently possible, to burn over the stubbles before the follow- 

 ing year and to plough down the land deeply before the next crop is sown. The burn- 

 ing will destroy a great many of the insects, and the ploughing will put them so deep 

 down that the delicate flies, when they emerge, cannot reach the surface. In years of 

 bad infestation a great effort should be made to get as much fall ploughing done as 

 possible, so as to reduce the danger of infested stubble fields being left for summer- 

 fallowing, owing to the pressure of spring work. As it is necessary to cut low to pick 

 up fallen .grain, many of the flax-seeds will be carried with the straw. At threshing 



