1924 ENTOMOLOGICAL SOCIETY 39 



THE ONION MAGGOT IN THE OTTAWA DISTRICT 



G. H. Hammond, Entomological Branch, Dominion Department of 



Agriculture, Ottawa 



Since the latter part of the 19th century the onion maggot has been regarded 

 as an insect pest of primary importance in the Ottawa district. Early records 

 indicate that in 1875 Mr. William Couper found the maggots to be destructive 

 throughout Ontario, as well as in other parts of eastern Canada. Dr. James 

 Fletcher, in his annual report for 1885, mentioned a case in which a Nepean farmer 

 experienced a loss of 75 per cent, from the onion maggot. During more recent 

 years losses from the onion maggot in fields near Ottawa have ranged from 

 1 per cent, to 95 per cent., but the average annual losses during 1922 and 1923 

 have been comparatively light, not exceeding 25 per cent. 



At Ottawa the eggs of the onion maggot have been taken on garlic, leek and 

 onion. During July and August, 1922 and 1923, it was observed that many 

 more eggs were taken on leek than on onion under garden conditions; never- 

 theless, it should be stated that fewer larvae feeding in garlic and leek material 

 matured. 



The attack of first generation larvae to the plants in June is by far the most 

 important form of injury. In the field during 1923, at Ottawa, such injury in 

 the form of a distinct wilting readily seen by the naked eye first became apparent 

 on June 12th in seedling plants, but was most evident between June 20th and 

 June 30th. Larval attack in midsummer and autumn produced malformations 

 of the bulbs and losses in weight. Secondary flies, such as Fannia sp., Muscina 

 stabulans and Muscina assimilis were found in decaying onions associated with 

 the larvae of the onion maggot but in no case were these secondary flies of primary 

 importance. 



Life History 



Two distinct generations of the onion maggot and a partial third generation 

 were reared during 1923. Only 89 second generation puparia out of 766, or 

 13 per cent., produced adults during the latter part of the season; the greater 

 number of the third generation larvae resulting from these adults, failed to pupate 

 by November 1st. The season of 1923 was cooler than normal and considerably 

 more moist. In an open and warm year doubtless a higher percentage of the 

 third generation adults would have developed. 



In 1922 eggs were collected first on May 24th, and in 1923 on May 26th. 

 The last eggs taken in the field during 1923 were collected on October 20th. Of 

 16,000 eggs collected in 1923 from a stated area, 2 per cent, were deposited in 

 May; 48 per cent, in June; 11 per cent, in July; 25 per cent, in August; 12 per 

 cent, in September, and 2 per cent, in October. The majority of these eggs were 

 laid in the soil, but on fine days immediately after a heavy rain, fully 95 per cent, 

 of the eggs were laid on the foliage of the plants, the size of the plants having no 

 appreciable relation to the location of the eggs at any period during the season. 



The egg stage averaged five days. The larval stage of first-generation 

 individuals varied from eleven to twenty- two days, but the great majority of 

 them took from eighteen to nineteen days to mature. The puparium stage 

 varied from eleven to twenty days, the average being fifteen days. 



The individual second-generation larval period varied from fourteen to 

 forty-eight days, with an average between July 25th and August 15th of twenty- 

 one days, and between August 15th and September 15th of twenty-eight days. 



