32 THE REIPOET OF THE No. 36 



THE PRESENT STATUS OF THE HESSIAN FLY IN 

 WESTERN ONTARIO. 



H. F. Hudson, Dominion Entomological Laboratory, Strathroy. 



The Hessian fly during the past season has inflicted a considerable loss on 

 farmers in Western Ontario, particularly in the counties of Essex, Elgin, Kent, 

 Middlesex and Lambton. While it is difficult to estimate the financial loss en- 

 tailed, it may be stated that in some cases the crop has been entirely ruined, necess- 

 itating the planting of other grains, while very few fly-infested fields averaged 

 more than ten bushels of grain per acre, and on the lighter soils the yield was 

 • reduced to five bushels per acre. This loss is due entirely to the " fly/' for in 

 localities where the fly was not present the yield of wheat ran from thirty-five 

 to forty-five bushels per acre. For the past three years repeated warnings have 

 been sent out, telling the farmers of the presence of the insect, and that once 

 a crop was infested nothing could be done to prevent the injury, but in spite of 

 all warnings the custom that prevailed was to sow as early as possible, with the 

 result that conditions so favoured the increase of the pest, that more loss has 

 been entailed this year than for a number of years past. Investigation work has 

 not yet reached that stage where it is possible to give a "fly-free" date to all 

 these localities, but in connection with our experimental work, the progress made 

 toward this end is decidedly satisfactory. 



In the fall of 1919 it was noticed that the insect was on the increase, and 1/10 

 of an acre wheat plots were planted at different dates to ascertain the fly-free date 

 for that year. Careful daily observations were made on these plots until 

 October 5th, when no more flies were observed on the wing. This work was again 

 checked up in the early spring before the middle of April as an infested plant 

 could be more easily determined in the spring. It was found that wheat planted 

 September 18th, was only slightly infested, and a later sowing made September 

 25th was free. This seems rather remarkable, as the flies were on the wing in 

 small numfbers until October 5th. It may be that the female flies live for a short 

 time after their ovaries are " spent," as no oviposition was observed in October. 

 One thing is quite certain, and that is, that no wheat should 'be sown in August, as 

 an examination in early spring showed that between 70% and 90% of August sown 

 wheat was killed by the fly where no fertilizer was applied. Where fertilizer 

 was applied the injury ran from 30%-50%. A gradual decrease in injury followed 

 the later sowings and an extra sowing put in in October and treated with fer- 

 tilizer was the most promising of all. The fertilizers used were : — lime only at 

 the rate of 1,000 lbs. per acre, acid phosphate, 200 lbs. per acre, lime and acid 

 phosphate mixed, and no treatment. Infested August sown wheat ran from two 

 to ten flax-seeds to the plant. On May 5th, 1920, the first female fly was observed 

 on the wing in the field. The weather from that date until May 16th was de- 

 cidedly cool and wet, but emergence was very active 'May 17th. Under field con- 

 ditions emergence was practically complete May 21st. No flies were observed on 

 the wing in the field after May 25th. These plots were subsequently harvested, 

 but the infestation was so heavy in all the plots, that the wheat was mowed with 

 a scythe and thrown to chickens; it is doubtful if there was a bushel of grain 

 on the whole experimental field. A similar experiment was duplicated this fall 

 on the same ground. The soil was thoroughly worked, the stuhble carefully 

 buried, and the field manured with barn yard manure, reinforced with 

 acid phosphate. The first sowing was made September 15th; second sowing, Sep- 



