THE CARROT RUST FLY 7 



report that this species was reared from turnip and rape, and Pettit (23) refers 

 to a report of it in potato; but in Massachusetts it has been found attacking only 

 plants of the botanical family Umbelliferae, and evidently the members of this 

 family are at least preferred as food. 



SUSCEPTIBILITY OF VARIETIES OF CARROTS 



Test plantings of strains and varieties of carrots were made at Waltham from 

 1929 to 1932 and records taken on the infestation by both the first and second 

 generation of the carrot rust fly. In 1929 the field infestation was quite heavy 

 and resulted in serious injury to 46 and 47 percent of the plantings of Nantes 

 and Henderson's Intermediate. In 1930, 1931, and 1932 the field infestation was 

 much lighter, and the injury to the various varieties of carrots was nearly equal. 

 The last five strains of garden carrots listed in Table 3 were planted only in 1932 

 when the infestation was very light, and consequently the results are not signifi- 

 cant, although 10 percent injury to Table Gem by the second generation in 1932 

 indicates probable severe injury to this carrot if subjected to a heavy infestation. 



Of the garden varieties, it is apparent that the short, thicker varieties such as 

 Chantenay and Scarlet Horn are less seriously damaged than the longer varieties 

 such as Hutchinson and Intermediate, and yield records from Nova Scotia 

 (1) confirm these observations. 



At Waltham the stock carrots were generally more heavily infested than the 

 garden carrots, as a group. Gorham (correspondence) states that in New Bruns- 

 wick the white carrots suffer less injury than the red carrots, but at Waltham the 

 White Mastodon and White Belgian varieties were very severely damaged in 

 some cases and suffered more injur\ than the Long Orange Belgian. 



NATURE OF INJURY 



Plants are damaged only by the feeding of the larva, and on such crops as 

 carrots and parsnips the injury occurs entirely below the surface of the ground 

 (Plate 1 and 3). The first feeding causes narrow rust-colored furrows in the outer 

 epidermis. These furrows are about 1/16 inch deep and may be round, narrow 

 trails or blotchy, irregular areas with the epidermis broken in many places. 

 They tend to proceed horizontally but are not consistent in this respect. In young, 

 tender carrots the root just above the growing tip is generally attacked, and, if 

 the plant is not killed by this injury, a stunted, bulbous, or irregular-shaped 

 carrot results (Plate 2). In mature carrots tunnels may be made in any part of 

 the root, and in severe infestations the tunnels may extend through the root 

 from one side to the other, although this seldom occurs in types having a distinct 

 fibrous core (Plate 4). 



When infested carrots are stored in the fall, many larvae in them are still 

 immature and continue feeding while the roots are in storage. In fact, it was 

 injury of this kind which resulted in the first discovery of this insect in Canada 

 and Maine. In light infestations, the presence of the maggots is often unnoticed 

 at harvest, and much unexpected damage from late feeding by the maggots is 

 found when the carrots are removed from storage. 



The foliage of infested carrots, especially that of immature plants, is usually 

 thin and often has a red or yellow color which is more pronounced in the older 

 leaves. 



Parsnips are injured in the same way as carrots, (Plate 1). In celery and parsley, 

 the feeding roots are eaten, and tunnels in the fleshy stems above ground are 

 present when the infestation is severe. 



