4 MASS. EXPERIMENT STATION BULLETIN 412 



Puparium 



Elongate-oval, rounded at both ends, with noticeable forked tubercles, about 

 1/4 inch long and dark brown in color. The puparia are usually found near the 

 surface of the soil and within four or five inches from the root of the plant on 

 which the larvae developed. During the summer the pupation period is ten to 

 twenty days, but those larvae which pupate in the autumn live in the puparia 

 through the winter (Figure 2-C). 



Adult 



A bristly black fly with gray markings, resembling the common house fly 

 but smaller and quicker in its movements. At rest, the wings are held flat against 

 the body. There are three dark longitudinal lines on the back of the thorax. 

 The average length is about }/i inch, and the abdomen of the male is much 

 smaller than that of the female. During the oviposition period the female flies 

 crawl and hop over the soil near the stems of the host plants (Figure 2-D). 



SEASONAL HISTORY 



There are normally three generations annually, with the majority of the flies 

 appearing in May, July, and September and being active for about a month 

 at each period. The average life cycle requires five to seven weeks, and this 

 period is influenced a great deal by temperature and moisture. In Massachu- 

 setts the first generation, which attacks early cabbage and related crops, is by 

 far the most destructive and abundant. The second generation is the least de- 

 structive, and although many maggots live on the stems of mid-season cabbage 

 cauliflower, and broccoli, the principal damage to garden crops by this generation 

 occurs on radishes planted between June 10 and 30. The third generation 

 maggots feed in turnips, late radishes, and especially in the stumps of cabbage 

 and related crops which are left in the field in September and October. (See 

 Table 3.) 



Table \. Relative Susceptibility of Host Plants to Attack by 

 Cabbage Maggot. Waltham, Massachusetts. 



crop percent of plants infested 



1930 1931 1932 1934 1937* 1938* 1939* Average 



Cabbage** 5i 75 96 86 95 77 87 78.4 



Cauliflower 37 89 58 100 71.0 



Broccoli 14 58 84 52.0 



Brussels Sprouts 16 62 56 44.7 



Radish 71 83 92 37 45 65.6 



Turnip (Purple Top) . 21 21.0 



Kohlrabi 84 84.0 



Chinese Cabbage ... . 64 64.0 



CoUards 88 88.0 



* Commercially injured = moderate or severe injury, or dead (omits slight or very slight 

 infestation). 



** Copenhagen Market or Golden Acre variety. 

 1930-1934 records refer to infested plants. 

 1937-1939 records refer to plants showing commercial injury. 



