180 Life- History of the Onion Fly 



Wings: hyaline, with the third and fourth longitudinal veins nearly 

 parallel to each other, and the external transverse ones straight, and a 

 Ijttle oblique; Calyptra and Halteres both pale yellow. 



Legs: sometimes piceous; hind femora almost bare of hairs or bristles 

 at the base of their under surfaces; hind tibiae of the males furnished 

 with a few short bristles along the middle and upper part of their inner 

 sides. The female is very similar in colour to the male; the eyes are 

 widely separated, the intervening space being red at its front part; the 

 abdomen is dull grey mostly immaculate, conical and pointed at the 

 apex; the calyptra are white and the halteres yellow." 



Fig. 6 is a drawing of the female Onion-Fly. 



Length of Life of Adult Fly. The writer was unable to determine the 

 length of life of the adult flies under natural condition. In the laboratory, 

 however, they showed considerable longevity. At room temperatures 

 and fed on casein, the flies lived for periods ranging from three weeks to 

 two months. 



This may be partly due to the artificial conditions of feeding and the 

 absence of natural enemies, etc. In this connection it is worth mentioning 

 that the flies refused to feed upon sugar and water in captivity but fed 

 readily upon casein. 



This is curious when it is considered that the "poisoned bait" method 

 of control, which consists of poisoning the flies with molasses and sodium 

 arsenite, is so largely used. This possibly may be explained by the 

 difference in the sugars used. 



Development and Number of Generations. From observations made 

 during the summers of 1920 and 1921, both in the field and in the 

 insectary, it appears that there are three generations of Hylemyia 

 antiqua in a season, the third being incomplete. There is no well- 

 marked division between the broods but each one overlaps the other, so 

 that maggots in all stages, puparia and adults are found throughout 

 the summer. 



In the unusually hot autumn of 1921, the larvae of the third genera- 

 tion were found attacking autumn sown onions, quite late in October. 



The adult flies hatched from overwintering puparia were first noted 

 on the wing on May 8th, though odd specimens have been known to 

 hatch in a mild winter as early as January 25th. 



The flies were first observed in the onion fields on May 30th and 31st 

 and in much larger numbers during the early days of June. The maggots 

 of the first generation commenced hatching on the second of June. These 

 had mostly pupated by the end of the month. Flies of the first generation 

 commenced hatching at the beginning of the second week in July and 

 second generation adults were seen ovipositing on August 24th. 



