40 THE REPORT OF THE No. 33 



The average individual pupal period of the second generation was seventeen 

 days, with a minimum of fourteen and a maximum of twenty-five days. Success 

 attended our efforts to rear flies in continuous series from eggs collected in the 

 spring, and from these it was observed that second-generation adults oviposited 

 between July 20th and September 20th from the first female emergence on 

 July 6th, while the third generation adults deposited eggs between September 

 10th and October 17th. 



First-generation eggs were laid between May 26th and June 30th with first- 

 generation larvae present in the field between May 30th and July 15th. 



Many larvae were observed emerging from the egg. Emergence occurred 

 most frequently about 8.30 a.m., and took place through a narrow opening 

 extending from near the anterior end to about one-third the length of the egg. 

 The maggot when just hatched is glistening pearly white in colour and somewhat 

 longer than the egg. When full-grown it attains a length of 10 mm. and retains 

 the pearly colour without the lustre. 



The pre-oviposition period of adults under observation was thirteen days 

 in the third generation and fourteen days in the case of the second. Hibernation 

 occurs in the puparium stage, as has been noted by other investigators. 



Control 



Staphylinid beetles were observed to be predaceous upon eggs and larvae 

 of the onion maggot in confinement and their close association with infested 

 onions in the field leaves little doubt that they are also predaceous under natural 

 conditions. Furthermore, certain individual parasites belonging to this impor- 

 tant group of beetles were reared from first and second generation puparia. 

 Unfortunately these internal parasitic Staphylinids have not as yet been definitely 

 identified but from their appearance and habits it is probable they are the species 

 known as Baryodma ontarionis Casey, which is an important parasite of the 

 cabbage-root maggot and which has been noted by Gibson and Treherne (Bulletin 

 No. 12 of the Dominion Entomological Branch). During 1923, only .4 per cent, 

 of the onion maggot puparia under observation were found to be infested with 

 this parasite, but in 1919 as high as 25 per cent, were parasitised. This beetle 

 is apparently the most important parasitic natural control factor of the onion 

 maggot in the Ottawa district, but seems very variable in its degree of prevalence. 



Among the Ichneumonids, *Aphaereta muscce Ashm., was reared from first- 

 generation puparia in 1923. The first adult parasites emerged on July 25th, five 

 appearing from a single puparium. Small, irregular holes in the anterior end of 

 the puparium, marked the place of exit. The Figitid, Cothonaspis gillettei Wash., 

 was also reared from second-generation puparia in August and September, eight 

 specimens (all males) emerging from two puparia. The percentage of paras- 

 itism of this latter species from material under observation was .83 per cent. 



Mites were also taken on adults of the onion maggot, being attached to the 

 abdomen and to the front legs. These were determined by Mr. H. E. Ewing, of 

 the United States National Museum, as probably Micro trombidium sp. 



Spiders are undoubtedly important enemies of the adult fly, some of the 

 experimental work during the last year being affected through their depredations. 



Remedial Measures 



In the Ottawa district the sodium arsenite poison bait method of control has 

 for several years been experimented with, but in some years this method of control 



* Both parasites were kindly determined by Mr. H. L. Viereck. 



