June, '15] 



SEVERIX-SEVERIX: IMPORTED OXIOX FLY 



343 



Under field conditions the incubation period of eggs deposited by the 

 first brood of flies in early June varied from three to four days. The 

 larval period was completed in two to three weeks in green onions, 

 onion-sets and small seeded onions, but in seeded onions from the 

 previous year, the development of the maggots was often prolonged 

 and, in some instances, required from four to five weeks. The pupal 

 period under field conditions required from nine to sixteen days during 

 the latter part of June and early July, the majority of the second 

 brood of flies emerging in eleven, twelve and thirteen days. 



Several experiments were performed to determine whether the 

 imported -onion fly could complete its life history in food material other 

 than the onion. In one instance, fourteen eggs immediately after 

 deposition in an onion field, were placed below the surface of the soil 

 in contact with, radishes growing in a flower pot. Fourteen onion flies 

 completed the different stages of their life cycle in twenty-nine to 

 thirty-five days in the radishes. In a second experiment freshly laid 

 eggs were transferred from onions to manure. The next day the eggs 

 were shriveled in appearance and an examination of the manure dis- 

 closed the presence of numerous mites, that had undoubtedly sucked the 

 eggs dry. The experiment was repeated but this time fresh horse drop- 

 pings were used. The different stages of the life history in the manure 

 were completed in twentj'-nine to thirty-one days, except one fly which 

 required fifty-two days to pass through the egg, larval and pupal periods. 



An attempt was made to determine the number of days required after 

 emergence of adults from puparia before fully developed eggs appeared 

 in the ovaries. A large number of adults of the second brood, which 

 emerged on the same dsLj, were conflned in breeding jars containing 

 onions planted in wet sand. The specimens were fed daily on diluted 

 molasses, and water was sprayed into the jars with, an atomizer. 

 Daily dissections of specimens confined in breeding jars showed that 

 one of ten females had ripe eggs in the ovaries kt the end of twelve 

 days, but other females did not show mature eggs in the ovaries at the 

 end of sixteen days. In all probability, the effect of confining the in- 

 sects in breeding jars as well as the food material employed, played an 

 important role in the rate of development of the eggs. 



Through dissections of female flies of the flrst and second broods, it 

 was found that the average number of apparently full-grown eggs 

 present in the ovaries varied from forty-one to fifty-one. In all prob- 

 ability, the onion fly empties its ovaries of a batch of about fifty eggs, 

 depositing from one to fifteen eggs at a time, a second batch of eggs 

 probably then develops, ripens, and is deposited and so on. 



The period of emergence of the second brood of onion flies under 

 field conditions extended from June 28 to July 25, most of the flies 



