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Gibson (A.) & Treherne (R. C.)- The Cabbage Root Maggot and its 

 Control in Canada, with Notes on the Imported Onion Maggot and 

 the Seed-corn Maggot. — Dominion of Canada Dept. Agric, Entom. 

 Branch, Ottawa, Bull. no. 12, 1916, 58 pp., 29 figs., 10 tables, 

 1 chart. [Received 14th June 1916.] 



Chortophila {Phorbia) brassicae, Bch. (cabbage root maggot) occurs 

 throughout Canada, attacking cabbage, turnip, cauhflower and other 

 Cruciferous plants. Eggs laid on or near the base of the host plant 

 hatched, in 1915, in from three to five days under outdoor conditions, 

 the degree of fcrtihty being 86-9 per cent. When incubated at 

 temperatures between 80° and 85° F., 95 per cent, hatched in from 

 three to five days under moist conditions and 50 per cent, in the same 

 time in dry air. The duration of the larval stage varied from 19 to 32 

 days. Pupation takes place in the root tissues, or in the soil close to 

 the root or at a distance of 4 or 5 inches away. Overwintering pupae 

 were found at a depth of from 1 to 9 inches. The duration of the pupal 

 stage varies very considerably according to the temperature. At 

 Agassiz, B.C., where the average temperature for March was 41° F., 

 adults emerged from overwintering pupae on 8th April ; in Ottawa, 

 w^here the average temperature was 19*3° F., pupae collected on 25th 

 April transformed between 20th May and 6th July. The average 

 length of the adult stage was 3 '5 days at the end of June and nine days 

 at the end of August and during September, the variations shown 

 ranging between 2 and 5 days and 7 and 25 days at these periods. 

 The sexes were present throughout the season in practically equal 

 numbers. 



At Agassiz, in 1915, oviposition was first observed on 10th April and 

 continued until about 1st June. Adults from the earliest eggs 

 appeared at the end of May, while those from eggs deposited late did 

 not emerge until the beginning of July. In eastern Canada, flies of 

 the first generation emerged from 21st to 27th June. The first eggs 

 of the second and third generations appeared at Agassiz during the 

 first week in June and the end of July respectively. A complete or 

 partial fourth generation may occur, according to autumn conditions ; 

 at Agassiz egg-laying continued until 22nd October. C. brassicae has 

 thus at least three complete generations which show much overlapping, 

 so that all stages of development occur at any given time. In the 

 Ottawa district injury to cabbage and cauhflower plants is most 

 marked during May and June. Radish crops grown at Agassiz during 

 May are frequently severely damaged. It is probable that no varieties 

 of cabbage or cauliflower are immune to attack. Observations on the 

 oviposition habits showed that the majority of eggs are deposited on 

 the stem or in the crevice between the stem and the soil. Untreated 

 cabbage and cauliflower plants which died as the result of attack 

 reached a total of 12*1 and 11*4 per cent, respectively. Eggs were 

 apparently laid more freely on or near strong, long-stemmed plants. 

 The preoviposition period under insectary conditions during July was 

 about six days. The winter is passed in the pupal stage. 



Hylemyia antiqua, Mg. (imported onion maggot) is a pest of onions 

 throughout Canada. The eggs are deposited on the young leaves, on 

 the outside of the stem near the soil or on the soil itself. During 1915 

 the first eggs were observed at Ottawa on 4th June. The eggs hatch 



