1924 ENTOMOLOGICAL SOCIETY 43 



adults commenced egg-laying on July 19th, and continued until September 8th, 

 giving rise in turn to maggots and puparia. Adults of the third generation first 

 appeared in the vials on August 21st and continued to emerge until October 3rd. 



The average larval life of the first generation, estimated from twelve separate 

 series of egg collections, was determined as being thirteen days ; the average pupal 

 life being estimated as 15.77 days. 



The larval and pupal life of the second generation was increased somewhat. 

 For the larval period the average was 16.4 days, and for the pupal stage 19.8 days, 

 in cases where flies did emerge. 



From material reared in series from July until October, 81.4 per cent, of the 

 second-generation puparia did not produce adults during 1923 but hibernated. 



From egg counts made at regular three to four-day intervals throughout the 

 season it was determined that the greatest number of eggs were laid during June 

 and August. In May 2 .3 per cent, of the total number of eggs were laid ; in June, 

 36.1 per cent.; in July, 8.9 per cent.; in August, 39.6 per cent.; and in Sep- 

 tember, 13.1 per cent. 



In short, first-generation eggs, larvae and puparia were present in the field 

 from May 30th until August 4th. Second-generation eggs, larvae and puparia 

 were present, from July 23rd until October 4th, 81.4 per cent, of these puparia 

 overwintering. 



Attempts made to breed second-generation adults in a large field cage (6 ft. x 

 6 ft. x 3 ft.) proved unsuccessful. However, third-generation flies placed in this 

 cage on August 24th, 27th and 29th, respectively, bred and laid eighteen eggs on 

 September 17th, and forty-two eggs were collected from the onions in the cage 

 on September 24th. 



Some maggots were reared successfully on onion agar, more especially on 

 agar to which a little hydrochloric acid had been added. Out of twenty maggots 

 fed on this agar three went into pupation and one fly emerged. 



As regards the oviposition habits of the flies it was observed that during the 

 spring and summer, until the plants all attained a size of approximately six to 

 eight inches, practically all of the eggs laid were deposited in the soil within one 

 or two inches of the plant. Towards the end of August and during September 

 eggs were commonly laid on the leaves, as many as eight to fifteen eggs being 

 taken at one time on a single plant. It was observed during midsummer that 

 those onions injured or attacked by first-generation larvae were frequently chosen 

 by second-generation adults for oviposition. Plants affected by onion smut also 

 proved attractive for the flies in August. 



These selective habits are doubtless of great importance in view of the 

 possible use that may be made of volunteer onion growth as a means of control 

 during the spring months. 



Remedial Measures 



In applying the sodium arsenite poison bait according to the formula laid 

 down in Pamphlet 32 of the Dominion Entomological Branch, two methods of 

 application are suggested, viz. : the sprinkling of the bait across the field in large 

 coarse drops, or the setting out of suitable containers at regular intervals through- 

 out the field filled with the liquid. 



Prof. Lochhead and Mr: W. J. Tawse, 1 in conducting experiments in the 

 Montreal section in 1921, using these two methods, found that the sprinkling of 

 the bait was not nearly so successful as where bait pans were used alone. In 



1 1921: Lochhead, W., and Tawse, W. J.: Fourteenth Annual Report of the Quebec Society 

 for the Protection of Plants. Pp. 43-48. 



