1924 ENTOMOLOGICAL SOCIETY 37 



storms were very severe, as wind and hail were combined with the rain. The 

 excessive moisture made much of the observation work disagreeable, and ovi- 

 position very irregular. In at least one instance a hailstorm was undoubtedly 

 responsible for the destruction of many of the flies. 



Seasonal History 



Flies and eggs were first observed in the field on May 15th. At this time 

 seedling onions were about three inches high, but there were several volunteer 

 onions scattered throughout the garden and ten of these were selected for ovi- 

 position records. Eggs were collected every day and counted until oviposition 

 ceased. The daily average number of eggs per plant for the first generation was 

 24.6 with the height of oviposition centred on May 22nd and 23rd, no eggs of 

 this generation being found after July 7th. Some of the first and last eggs of 

 this generation were taken to the laboratory to get the limits of the generation. 



The first larvae hatched in the laboratory in three days, and the average 

 larval period of 54 individuals which reached maturity was 16.35 days, with a 

 range ofirom 12 to 22 days. The last larvae to hatch from eggs of this generation 

 had the same incubation period, but the larval period averaged 18 days with a 

 range of from 15 to 26 days. 



The first larva pupated on June 2nd and the earliest fly emerged on June 

 22nd, the average pupal period of the 54 flies being 20.37 days with a range of 

 from 19 to 22 days. The last larvae of this generation pupated on the first of 

 August and emerged on the 20th of August, having the same average pupal 

 period as the first. 



The first eggs of the second generation were secured in the field on July 13th. 

 Adult flies had been collected earlier than this and many had been reared, but 

 no eggs were secured in the breeding cages and the weather was not suitable for 

 extended searches in the field. From this date on, eggs were found until the 

 22nd of August with the height of oviposition on the 23rd of July. The daily 

 average number of eggs per plant for this generation was 7.25 based on observa- 

 tions made on ten seedling plants. 



None of the first eggs of the second generation collected in the field were 

 fertile and in general the fertility of this generation was much lower than that of 

 the first generation. The eggs of the first generation hatched over 80 per cent, 

 healthy maggots, whereas barely 35 per cent, of the eggs of the second generation 

 hatched at all. This may possibly be due to the destruction of numbers of the 

 male flies by a severe hailstorm which occurred on July 1st, thus forcing the 

 females to deposit infertile eggs. The above figures are based on records ob- 

 tained by hatching eggs on wet blotting paper in petri dishes. 



The first larvae of the second generation were secured on July 26th from eggs 

 collected three and four days previously, the larval period averaging 18.2 days. 

 These larvae pupated and the first flies emerged twenty days later, on the 31st 

 of August. 



There is considerable evidence of a third generation, but this point was not 

 proved. The examination of onions harvested during the third week in Sep- 

 tember revealed the presence of numbers of nearly mature maggots, and several 

 very small ones which could easily have come from eggs laid since the emergence 

 of the third generation of flies. The examination of sets on the 18th of October 

 revealed large numbers of pupae and many half-grown larvae. There is little 

 doubt that the pupae developed from the last larvae of the second generation, but 

 the larvae can hardly be considered as belonging to that generation. 



