182 Life- History of the Onion Fly 



finally lie prone on the ground, the bulb in bad cases being reduced to 

 a rotting semi-liquid mass. Any number of maggots from 3 or 4 to 25 or 

 30 may be found in one onion bulb. 



The maggot, as a rule, enters the onion at the base and works its way 

 upwards, occasionally, however, it enters at the side. PI. XI, fig. 7 shows 

 onion bulbs destroyed by the maggots. 



Reproduction. Oviposition. The eggs are laid on the onion plant, in 

 clusters of half a dozen or more and sometimes as many as twenty or 

 thirty may be found together. They are deposited usually under the thin 

 sheathing leaf surrounding the stem, or in the crutch formed by the 

 outside leaf and the stem. Occasionally the eggs are deposited in cracks 

 in the soil but the more usual procedure is to lay them on the plant 

 itself. The attachment is very slight and eggs found on the surface of 

 the soil beneath the onion have usually been detached by some external 

 agency such as rain or wind. 



Pre-oviposition Period. This is an important phase in the life of the 

 Onion-Fly and more so in the light of recent attempts to control this 

 pest by means of poisoned bait intended to kill the fly during the ovi- 

 position period. 



Sanders (2) puts this period at ten to fourteen days, while Severin 

 and Severin (i) give twelve to sixteen days as the time. 



This is a point difficult to determine with any great degree of accuracy 

 owing to the probable effects of the artificial conditions of captivity 

 upon the development of the fly. 



From dissections of flies in the laboratory at varying periods from 

 the time of emergence, the writer is inclined to put the time of maturation 

 at a week and sometimes as long as nine or ten days. 



Hibernation. The usual method of hibernation is undoubtedly in the 

 pupal condition. There are cases on record, however, which show that 

 the larvae are also capable of passing the winter. 



According to some authors (3) the insect hibernates as an adult but 

 confirmation of this fact is lacking. 



Parasites. One Hymenopterous parasite belonging to the order 

 Braconidae was bred from Onion-Fly pupae, the species being Apha- 

 creta cephalotes. This parasite was responsible for largely reducing the 

 numbers of the later generation of Onion-Flies in the summer of 1920. 

 As many as fourteen fully developed adults were dissected from one 

 pupal case of the Onion-Fly. 



The parasite also attacks the larvae of Psila rosae, the Carrot-Fly. 

 Fig. 8 is a drawing of Aphacreta cephalotes and fig. 9 its pupa. 



Another useful natural enemy is a beetle Aleochara bilineata belonging 

 to the order Staphylinidae or "Rove" Beetles. The larva of this insect 



