44 THE REPORT OF THE No. 33 



view of this, in 1923 our experiments in control only considered the value of these 

 pans, and in order to give the method every opportunity to prove successful they 

 were kept refilled for the entire period from May 22nd until July 10th. The. 

 commercial aspect bearing upon the point as to how many times refillings were 

 necessary was not specially considered. Five acres were treated by the pan 

 method, using about thirty pans to the acre. At the close of the season an 8 per 

 cent, loss was observed in the plantation, and a total of 405 eggs and eggshells 

 were actually taken on ten feet of row in twenty-three separate observations 

 between June 11th and September 5th. 



In a two-acre check or untreated field adjoining the above the net loss was 

 3.3 per cent., with a very much lower egg count throughout the season. To 

 account for this negative result it would be only fair to state that while the 

 conditions were as nearly comparable as it was possible to make them, the 

 untreated field had not been manured so heavily and this fact may partly account 

 for the lower degree of infestation if the attractiveness of the poison bait pans in 

 the adjoining field is discounted. 



As mentioned in Pamphlet 32 of the Dominion Entomological Branch, Mr- 

 W. J. Tawse made a suggestion that possibly encircling the bait pans with a 

 number of growing cull onions would prove a more satisfactory and reliable 

 remedy than where pans are used alone. This recommendation was based very 

 largely on the suggestion made by Messrs. R. C. Treherne and M. H. Ruhmann, 1 

 where trap onions are used alone in British Columbia, coupled with his belief in 

 the value of sodium arsenite baits. 



In order to test the value of this combination method, six acres were set out 

 with pans and traps in adjoining fields to the plantation referred to above. At 

 the close of the season the loss due to onion maggot attack was noted, as 5.4 per 

 cent, with 408 eggs and eggshells being taken in ten feet of row in twenty-three 

 separate observations between June 11th and September 4th as before. Occa- 

 sional observations during the season indicated that eggs were being laid in fair 

 numbers around the trap onions, but no definite count of eggs or record was kept. 



However, from ten trap onions especially set for oviposition counts, a total 

 of 2,450 eggs were taken between May 30th and September 19th, 1,038 of these 

 eggs being first generation, 1,163 second generation, and the remainder, in all 

 probability, third generation. The degree of infestation this year has unques- 

 tionably been light which accounts for the slight damage that was caused and 

 for the low oviposition counts. The comparative value of the various control 

 measures is obtainable, however, from these records. 



In addition to the above, two acres of onion field were set out with the 

 special British Columbia poison-bait can, which only differs from the ordinary 

 open pie dish by the addition of a water reservoir and felt mat. No records of 

 oviposition or loss by onion-maggot attack were kept in this field, as the main 

 object was to test the value of this special pan over the open dish from a mech- 

 anical point of view. As a result of this experiment it was shown that the. 

 method did not prove any more desirable than the open dish with excelsior or 

 straw floats, and the trouble of refilling in a field where water was not easily 

 obtainable detracted very greatly from their use. 



As a result of this year's experiments it was unfortunate, from our point of 

 view, that a greater degree of infestation was not registered. In a broad, general, 

 commercial scale all fields used this year yielded equal returns and suffered a 



1 1921: Treherne, R. C, and Ruhmann, M. H.: Fifty-second Annual Report of the Entomo- 

 logical Society of Ontario. Pp. 29-33. 



