12 MASS. EXPERIMENT STATION BULLETIN 352 



in layers 2 inches deep and thoroughly examined. Of the 170 pupae recovered, 

 85.88 percent were in the top 6 inches of soil, being distributed as shown in 

 Table 6. 



Table 6. Depth in soil at which carrot rust fly hibernates 

 VValthani, Mass. 1927-1928. 



Depth of Soil Number of Pupae Percent of 



Inches Recovered Total 



Oto2 4 2.35 



2 to 4 38 22.35 



4 to 6 104 61.18 



6 to 8 18 10.59 



8 to 10 6 3.53 



OVERWINTERING GENERATION 



Pupation takes place within 4 or 5 days after the maggots become full grown 

 and enter the soil, and this may occur between September 1 and the time when 

 the soil freezes. 



Emergence of Flies 



The flies of the overwintering generation emerge about the time that early 

 carrots are 2 to 4 inches long. This varies with the season, and at Waltham the 

 period of principal emergence has been from May 20 to June 13. As shown in 

 Table 7 the earliest emerging fly was found on May 16, 1930, and the latest 

 on July 10, 1928. 



Table 7. Emergence of carrot rust flies — overwintering gener.\tion 

 Waltham, Mass. 1928-1932. 



DATE OF EMERGENCE 



Year Number of Period of 



Flies First Maximum Number Last Principal Emergence 



1928 349 May 29 June 7 July 10 May 31-June 13 (74.21%) 



1929 329 May 24 May 29 June 28 May 27-June 1 (55 72%) 



1930 721 May 16 May 22 June 24 May 20-24 (39.66%) 

 1932 347 May 20 May 25 June 28 May 24-27 (32.56%) 



The emergence of the flies is influenced by temperature, and in 1930 approx- 

 imately two and one-half times as many flies emerged on days when the average 

 temperature was 60° F. or lower as when it was above 60° F., as shown in Table 8. 



Further indications that relatively low temperatures are more favorable to 

 the emergence of the carrot rust flies were obtained in 1932 when 25 field-collected 

 pupae were placed in each of four constant-temperature cabinets about 6 weeks 

 before the normal emergence period. As shown in Table 9, more than 80 percent 

 of the pupae transformed at 55° to 65° F. while none transformed at 85° F. These 

 records show that the flies appear earlier at the higher temperatures but that few 

 of them survive. 



