THE CARROT RUST FLY 17 



Emergence of Flies 



Although the first flies of the first generation have appeared as early as July 

 21, the majority of them are present between August 1 and 20, and they may 

 continue to emerge until the first week in September. In 1928, 75 percent of the 

 flies emerged August 9 to 18, and in 1929, 85 percent of them emerged August 

 19 to 24. In the breeding cages these flies lived 4 to 5 days, or approximately 

 the same length of time as the spring emerging flies. 



The average time required for the development of the carrot rust fly from the 

 laying of the eggs to emergence of the flies has been 9 to 11 weeks, as shown in 

 Table 17. Some individuals have not completed their life cycle for 110 days, 

 and others have developed in 44 days. 



T.\BLE 17. Summary of the life history of the carrot rust fly 

 Waltham, Mass. 1928-1930. 



SECOND GENERATION 



Eggs of the second generation are laid during the month of August and their 

 abundance is considerably afi'ected by climatic conditions. Hot, dry weather and 

 general drought apparently reduce the number of eggs laid and also the survival 

 of those which are laid. Even in the insectary where the cages were shaded and 

 moistened each day, this generation of flies laid only about one-third as many 

 eggs as the overwintering spring generation flies. 



The average incubation period of the eggs of the second generation was 6.32 

 days in 1928 and 6.12 days in 1930, being approximately the same as the time 

 required for the incubation of eggs of the first generation. (See Table 17.) 



Most of the larvae hatch and enter the roots in August, but they may continue 

 to attack the carrots into October. As with the first generation, the feeding period 

 is about 4 weeks, averaging 27.25 days in 1930. The majority of the maggots 

 which enter the carrots after September 1 remain in them after they are dug and 

 stored, and may cause considerable damage to the carrots in storage where they 

 continue to feed at temperatures above freezing. If the carrots remain in the 

 soil, maggots may continue feeding in them until the ground freezes, and in some 

 seasons the larvae do not complete their development and enter the soil to pupate 

 until well into winter. In 1930 a larva reared in the insectary entered the soil 

 to pupate on November 5 after being partially exposed to freezing temperatures 

 several times. 



In both 1929 and 1930, a few second generation flies were reared in October, 

 but, although they were handled by the usual insectary methods and lived for 

 several days, they failed to lay eggs. 



