18 THE REPORT OF THE No. 36 



Poisoned molasses traps give more promise for controlling noctuid moths than 

 •do other methods tried because : — 



1. They require attention, at the most, once a week. 



2. Females are attracted as readily as males to 'bait and they are usually gravid. 



3. With a combination of quassia and arsenic very few females that feed on 

 the bait are able to lay eggs subsequently. 



4. Quassia is non-poisonous to stock and is distasteful to them. 



5. Individual traps attract more moths than do corresponding troughs of 

 molasses. 



6. All materials are cheap and are readily obtainable anywhere. 



7. The bait is effective by day as well as by night and its efficacy is not re- 

 duced by moonlight. 



8. Climatic conditions affect the traps very little. 



THE WESTERN WHEAT-STEM SAWFLY IN CANADA. 



NORMAN CRIDDLE, DOM. ENTOMOLOGICAL LABORATORY, TREESBANK, MAN. 



The Western Wheat-stem Sawfly — Ceplius cinctus (Nort.) is a native insect 

 that has become a pest because of the introduction of cereals such as wheat and 

 rye. It originally lived in various native grasses such as Agropyron, Elymus, 

 Calomogrostis and Bromus. While confined to these food plants it fluctuated 

 from year to year according to the prevalence of flowering stems in which the 

 larva? lived, or to the presence of natural enemies. These two factors usually 

 kept the insect well in hand until the grains mentioned above were introduced 

 when abundance of new food became available. The sawfly, however, was slow 

 in adapting itself to the new conditions and it was only towards the beginning 

 of the present century that it finally became established in our grain fields. Since 

 then it has steadily increased. To begin with, only the edges of wheat fields were 

 attacked by the overflow from native grasses but gradually the adults flew fur- 

 ther afield until, eventually, whole fields became infested and in some instances 

 more than eighty per cent, of the wheat stem was cut by the larvse. Both 

 Saskatchewan and Manitoba suffered heavy loss in 1921, the total amounting 

 to several million bushels and in south-west Manitoba exceeding twenty-five per- 

 cent, of the crop. The insect is steadily spreading and so far as we can judge, it 

 will continue to do so until the entire spring wheat area is invaded. 



Natural Control. The Wheat-stem Sawfly appears to have been kept well 

 under control in the past by various natural factors which include natural enemies 

 and meteorological conditions. Of the natural enemies Hymenopterous parasites 

 seem to have played the leading part though there was, at times, quite a high 

 death rate brought about by an unknown cause apparently of a fungus origin. 

 The rainfall has always been an important factor because it has controlled the 

 insect's food supply by governing the number of flowering stems in which tue 

 larvae live. 



The sowing of cereals over large areas of country has entirely upset the con- 

 trol conditions that previously existed. Factors that were then of the utmost value 

 have been almost eliminated, the available stems of grain having done away with 

 the check of limited food supply, while for reasons that are only beginning to be 

 understood, the parasites so prevalent in grasses are unable to follow their hosts 

 into the grain fields. On account of these conditions the sawfly has practically a 

 -free hand, and as a result it has spread over large stretches of country. 



